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The 7 climate tipping points that could change the world forever - Grist | Grist

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The 7 climate tipping points that could change the world forever - Grist | Grist

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In 2019 an international team of scientists published a commentary in the celebrated science journal Nature, sounding the alarm of a planet in crisis - and calling for transformative change.

"We are in a state of planetary emergency," they wrote, departing from the usual sterility of scientific writing. "The stability and resilience of our planet is in peril."

Yes, they were writing about climate change, but of a particular kind: climate tipping points, elements of the Earth system in which small changes in global temperature can kick off reinforcing loops that 'tip' a system into a profoundly different state, accelerating heat waves, permafrost thaw, and coastal flooding - and, in some cases, fueling more warming. The planet has already warmed by roughly 1.2 degrees Celsius (2.2 degrees Fahrenheit) since the Industrial Revolution, and if humans keep flooding the atmosphere with greenhouse gases at the same rate, we're on track to increase that to 2.7 to 3.1 degrees C (4.9 to 5.6 degrees F) by the end of the century.

So those small changes are getting bigger - increasing the likelihood of triggering those reinforcing loops, known as positive feedbacks. (For example, warming increases the frequency of wildfires, which in turn increases the amount of carbon dioxide released into the atmosphere from burning trees, which leads to an increase in global temperature, which means, you guessed it, even more wildfires.)

The scientists identified various elements of the Earth system at risk of reaching points of no return. These elements broadly fall into three categories - ice, sea, and land - and range from the melting of the Greenland ice sheet to the death of coral reefs to the raging of more and more wildfires.

The concept of tipping points challenges the dominant understanding of how climate change fundamentally works, says Will Steffen, one of the Nature article's co-authors and an emeritus professor of climate science at Australian National University. Rather than a dial slowly turning up, tipping elements could compound, he says, combining to build a greater, planetary-wide tipping point. Alternatively, they could push one element out of whack, triggering another to fall out of phase, and then another in a domino-like effect, resulting in a "rapid acceleration of warming until the Earth stabilizes in another state." These possibilities are far from certain, he admits, but the consequences of a planetary tipping point are severe enough that even a slim risk needs to be taken seriously.

The particular danger, according to the Naturepaper's authors, is that even though change in a tipping element may happen slowly on a human timescale, once a certain threshold in the system is crossed, it can become unstoppable. This means that even if the planet's temperature is stabilized, the transition of certain Earth systems from one state to another could pick up speed, like a rollercoaster car that's already gone over the apex of a track.

Jacquelyn Gill is a paleoecologist at the University of Maine who studies physical records of Earth's ancient climate. She didn't work on the Naturepaper, but she says the evidence from Earth's history supports the idea of nonlinear climate responses, and that understanding this evidence can help us better understand what might lie ahead. "It's not just the matter of more CO2 equals more warming," Gill says. "There will be feedbacks."

For Steffen and his co-authors, including Tim Lenton, the director of the University of Exeter's Global Systems Institute, understanding the risks of tipping points requires a radical reframing of the climate challenge - and a more fundamental shift in human society than merely pumping successively fewer and fewer emissions into the atmosphere. "If we're right about the tipping points, they're not marginal," Lenton tells Grist. "They're existential risks."

When it comes to the climate crisis, the sea is both an unwitting ally and frequent victim. The world's five oceans - which cover 70 percent of its surface - absorb both heat and carbon dioxide, gobbling up at least a quarter of the emissions dumped into the air from the burning of oil, gas, and coal. Without them, the world would have already warmed so much, it would be virtually uninhabitable by humans.

But all that absorption comes at a cost. As heat rises, ice melts, and carbon dioxide pours into the ocean, ecosystems are thrown into disarray. Coral reefs are overheated, withered by extreme temperatures and dissolving in acidified waters. Currents that have been stable for millennia are starting to shift and change, inching toward collapse. In the far reaches of the North Atlantic and across broad swaths of the tropics, some climate tipping points may already be underway.

Atlantic Ocean circulation

Early in the 2004 film The Day After Tomorrow, climate scientist Jack Hall - played by a concerned-looking Dennis Quaid - receives a late-night phone call. It's a fellow scientist he'd recently met at a conference. "You recall what you said in New Delhi, about how polar melting might disrupt the North Atlantic current?" the scientist asks. "Well ..." the scientist continues, his voice trailing off. "I think it's happening."

What follows is hardly scientifically accurate - it's a Hollywood movie, after all. As a consequence of that disrupted current, tornadoes sweep across Los Angeles and a tsunami-like wave crashes into New York City. But while most of the film belongs in the realm of sci-fi (or " cli-fi "), the movie's central premise - that the collapse of one ocean current could have knock-on effects for the rest of the world - is true.

The Atlantic Ocean is dominated by a single current: a thick band of water that flows north from the Gulf of Mexico, hugs the southeastern coast of the United States, and then shoots up north toward the frigid outposts of Greenland and Iceland. Along the coast of the U.S., where the current is known as the "Gulf Stream," the water is warm - in the summer, it can reach a balmy 71 degrees Fahrenheit - but as it winds its way northward it gets colder and colder, releasing huge amounts of heat into the atmosphere. This current - known as the "Atlantic meridional overturning circulation," or AMOC for short - keeps the weather mild in cities like Berlin, London, and Paris, and scientists estimate that the energy it transports is roughly equivalent to the power provided by 1 million average-sized nuclear plants.

"This is not just a theory," says Stefan Rahmstorf, a climatologist at Potsdam Institute for Climate Impact Research in Germany. "It has happened repeatedly in the history of the Earth during the last ice age."

A collapsed Atlantic current could cause plummeting temperatures in the northern hemisphere, an extra foot and a half of sea level rise along the East Coast of the U.S., and more ferocious winter storms over Europe, according to modeling from the U.K.'s national weather service. Scientists say it could also rejigger agriculture, by mutating precipitation patterns around the world, endangering crop yields in Great Britain and Ireland, which would become more arid and cold.

While scientists know that the Atlantic current could shut down, nobody has a clear idea of when it could happen. In its 2014 summary of the state of Earth's climate, the United Nations Intergovernmental Panel on Climate Change, or IPCC, said it was " very unlikely" that the current would collapse during the 21st century, but that it was too difficult to predict what would happen after 2100. Other papers have estimated that the current could come to a stop with anywhere between roughly 3 and 5.5 degrees C (5.4 and 9.9 degrees F) of global warming.

"If we stay below 2 degrees Celsius (3.6 degrees Fahrenheit) of global warming, then it really is highly unlikely that we will have an AMOC shutdown," says Levke Caesar, a researcher at Ireland's Maynooth University. "But if we have other degrees of warming, we don't know."

According to Caesar's own research, the Atlantic circulation has slowed since the mid-20th century, and now carries around 15 percent less water than it once did. In another study, released in February, scientists argued that the current is at "its weakest state in over a millennium." A particularly dramatic slowdown from 2009 to 2010 was linked to an icy winter in western Europe and an abrupt spike in sea-level rise along the East Coast. (Some scientists, including Caesar, suspect the current pulls water away from the eastern seaboard; when it slows down, the ocean waters surge up again.) Thomas Delworth, a senior scientist at the Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, says that by 2100, the current could weaken by 30 to 60 percent - but "there's still a lot of uncertainty."

Even a total shutdown of the Atlantic current wouldn't happen overnight like in The Day After Tomorrow. Rahmstorf characterizes a potential collapse as more of a "winding down" that would take place over 60 to 100 years. But that "winding down" would drive wild weather changes, rising sea levels, and chilling temperatures from Spain to Scandinavia. And, like many scientists, Rahmstorf won't rule out the possibility of an earlier shutdown.

"If you say we are 90 percent sure nothing serious will happen by 2100 to the AMOC, that sounds reassuring to people," he says. "But it's not reassuring to me. A 10 percent risk is far too big."

Coral reefs

Scientists believe coral reefs throughout the world, such as this one off Champion Island in the Galápagos Islands, may have already reached a tipping point. Underwater Earth / XL Catlin Seaview Survey / Christophe Bailhache

Steph Gardner was nearing the end of her doctorate when the coral reefs she researched bleached for the first time. Her field sites were scattered along the Great Barrier Reef off the northeast coast of Australia - sections of the ocean that had begun to feel as familiar to her as the hallways of her own home. She knew where the large acropora coral was, with its hundreds of pointy fronds; she knew to make a right turn at a large, lumpy pillar called a bommie.

But this time, something was amiss. A marine heat wave had surged across the Pacific Ocean, dialing the water to 86 degrees F - the same temperature as a warm bath. Gardner's fellow researchers were coming up from the reef with tears in their eyes: The coral below had turned a ghostly, almost fluorescent white. "It was just like seeing a graveyard - absolutely gut-wrenching," says Gardner, who is now a researcher at the University of New South Wales in Sydney.

That was in 2016, the year of the largest and most devastating coral bleaching event in history. More than half of the corals in the northern, 435-mile-long stretch of the Great Barrier Reef died - some immediately, cooking in temperatures 4 to 7 degrees F above average. Others slowly starved over a period of months. And the bleaching wasn't confined to the coast of Australia. All over the world, reefs were turning white and dying off. Then, in 2017, it happened again. And then again in 2020.

"From my perspective," Gardner says, "we've already reached a tipping point."

Corals are strange creatures: minuscule animals that house tiny, friendly plants within their flesh and tentacles. In exchange, the plants help feed the coral, tinting their hosts a dusty pink or brown. But when water temperatures rise around 1 to 2 degrees C (1.8 to 3.6 degrees F) above average, that previously happy relationship breaks down. The plants rebel, spitting out toxic levels of oxygen. In response, the corals hastily jettison them, losing their color and standing out starkly bone-white against the rest of the reef - a process known as "bleaching."

A reef can survive if cooler temperatures return quickly, returning coral-feeding plants to their homes. Without them, many corals starve to death, their skeletons swallowed up by thick tufts of what looks like dark green fur. The "fur" are colonizing species of algae, which take over reefs when corals crumble. "What was once a living, vibrant reef becomes a reef of skeletons," says David Kline, a coral scientist at the Smithsonian Tropical Research Institute in Panama. "It becomes a morgue, covered over with slimy algae."

It's hard to identify a single, global tipping point for corals: Each reef is different, accustomed to different temperatures and living with different sources of stress. One reef, exposed to record-high temperatures, might die in a matter of weeks, already overwhelmed by an influx of smothering algae. Another might survive, protected by cold water welling up from the ocean floor. But as the planet warms, the ocean warms with it - and eventually most coral reefs will pay the price.

A healthy reef can take 10 to 15 years to return to normal after a catastrophic heat wave, but severe bleaching is now occurring every six years. According to the IPCC, 70 to 90 percent of coral reefs could disappear even if average temperatures remain under 1.5 degrees C (2.7 degrees F) of global warming. At 2 degrees of warming, nearly all of them - 99 percent - would vanish.

And it's not just rising temperatures that threaten the reefs. The ocean absorbs more than a quarter of the carbon dioxide humans spew into the atmosphere, and all that gas makes the water sharply acidic. If the pH of a reef drops too low, its corals won't just be overwhelmed by heat - their skeletons could start dissolving.

Ove Hoegh-Guldberg, a professor of marine studies at Australia's University of Queensland, says current rates of warming could soon make the planet inhospitable for reefs. "I believe you get to a point where the odds are so stacked, and the corals are so sick and poor, that we're just not going to have coral reefs anymore," he says.

That could be catastrophic for the millions of people who depend on reefs around the world. Despite covering less than 2 percent of the ocean floor, corals' complex structures house around a quarter of the planet's marine species. They also provide food, income, and storm protection for approximately 500 million people.

Despite the odds, scientists are continuing to help reefs recover any way they can, engaging in a Noah's Ark-type attempt to rescue - and re-introduce - as many corals as possible. Some are cross-breeding corals, trying to develop species that can withstand record-high temperatures and acidity; others are visiting distant coral outposts, like hot mangrove lagoons, to better understand how so-called " supercorals " are already surviving some of the most challenging conditions in the world.

"We've shifted into an emergency mindset," Kline says. "If we don't actively try to protect coral reefs, things are really going to change for the worse."

The Greenland ice sheet in the high Arctic and the Antarctic ice sheet that encircles the South Pole combine to hold 99 percent of the world's freshwater. If all of that water emptied into the sea, the oceans would rise hundreds of feet, permanently redrawing Earth's coastlines.

A growing body of evidence from Earth's geologic past shows that both ice sheets can melt rapidly when something - or someone - fiddles with the thermostat. Both appear to have tipping points that could lead to runaway ice collapse and irreversible sea-level rise. But reaching those thresholds varies dramatically from one pole to the other as a result of stark differences in the atmosphere and ocean currents surrounding each pole, as well as the geometry and scale of the two ice sheets.

Both ice sheets are effectively a vast mountain of ice draped over a continent (Antarctica) or a giant island (Greenland). Ice flows off these frozen mountains and into the surrounding seas through hundreds of enormous, frozen rivers, known as outlet glaciers. In parts of Greenland where outlet glaciers meet the ocean, the water is warm enough that these glaciers immediately start to melt and break up. But in the much colder seas surrounding Antarctica, they're often buttressed by floating ice shelves. Like corks in champagne bottles, these shelves help hold back the land-bound ice behind them - unless warming water starts to shake the shelves loose.

Greenland

It was early one May when Santiago de la Peña realized something wasn't right. The glaciologist had just hiked to Russell Glacier, located about 20 miles inland of Greenland's west coast. At that time of year, the glacier should have been frozen solid. But a river of meltwater had formed across its surface, creating a series of enormous waterfalls.

A landscape that should have been silent was reverberating with the roar of freshly melted ice making its way toward the sea. "I'd never seen so much meltwater at that time of year," says de la Peña, who has worked at field sites in western Greenland for the past decade.

That was 2019 - a record year for the loss of Greenland's ice. After an unusually warm spring followed by a late July heat wave that caused nearly the entire ice sheet's surface to start melting, Greenland would go on to shed 532 billion tons of ice into the sea that year. As a result, global sea levels are now permanently 1.5 millimeters (0.06 inches) higher.

A total meltdown of Greenland's ice sheet would raise sea levels much higher still - by about 24 feet. Though scientists estimate that it would take at least a thousand years for Earth's second-largest ice sheet to melt completely, years like 2019 are a reminder that Greenland is already undergoing a massive transformation with planet-wide consequences. Between 1992 and 2018, Greenland shed nearly 4 trillion tons of ice, and researchers worry that if carbon emissions continue to rise it could pass a point of no return within decades.

There are two key phenomena behind Greenland's melting - and if they accelerate and if future feedback loops amplify them, the ice sheet could plunge into a state of irreversible loss. One is mild summer weather and a warming atmosphere melting the sheet's surface, causing water to pool and run downhill into the sea. The thawing of fresh, white snowfall exposes darker, bare ice, which absorbs more of the sun's energy, triggering more melting.

The other is around Greenland's coasts, where rising ocean temperatures are destabilizing the edges of glaciers that funnel ice into the ocean. As these gateways break up, the frozen rivers they hold back start flowing faster into the surrounding sea.

Over the last 30 years, heat in the ocean and in the atmosphere has contributed roughly equally to Greenland's slimdown. But in recent years, the atmosphere has taken a larger role, as summertime heat waves supercharged by climate change trigger melt events like Greenland saw in 2012 and 2019. If those become the norm, dangerous feedback loops could kick in. One that's particularly troubling: As Greenland's surface melts, the ice sheet's elevation drops like a popsicle flattening onto a pavement. And as surface elevation falls, surface air temperatures rise, resulting in more melting.

Taken together, all of these processes could tip the ice sheet into a state of irreversible meltdown. One recent modeling study that looked only at surface melt found that 2.7 degrees C (4.9 degrees F) of global warming could push Greenland into a state of "sustained mass loss" - an effect known as "climate forcing" - where meltwater runoff exceeds snowfall accumulation year after year. But other models that consider both surface melt and coastal glacier retreat suggest Greenland's true tipping point might be as low as 1.6 degrees C (2.9 degrees F) - merely 0.4 degrees C (0.7 degrees F) above the current level of warming.

"Unless we figure out a way to rapidly reverse climate forcing, my opinion is that the ice sheet's doomed," says Ian Howat, a glaciologist at Ohio State University. Research Howat co-authored last year suggests that Greenland already passed a mini tipping point in the early 2000s, when dozens of coastal glaciers simultaneously started to retreat.

It's still possible, however, that we can lower our emissions quickly enough to prevent the ice sheet from entering full-on meltdown mode. It's also possible that Greenland's ice actually has no tipping point: In contrast to earlier work, a modeling study published in December found that negative feedbacks, like increased snowfall over Greenland's remaining ice as the ice sheet contracts, could prevent a runaway collapse and allow Greenland to restabilize at a smaller "steady state." Scientists are still investigating why some models predict this, though it may be that as the ice sheet retreats inland and Greenland's coastlines become flatter, moist marine air is able to migrate further inland before it rises and condenses into clouds, which can then produce snow.

Even in a catastrophic meltdown scenario, "we have to remember it's going to take a long time to lose the Greenland ice sheet," says Ruth Mottram, a climate scientist and glaciologist at the Danish Meteorological Institute. And how long exactly that process takes depends on our carbon emissions. A 2019 paper found that under a high-emissions scenario, the entire Greenland ice sheet could disappear within a thousand years. Under a moderate emissions trajectory, the ice could hang on for a few thousand more.

"It looks very different if we lose all of the Greenland ice sheet in the next one thousand years versus if we lose all of it in the next ten or twenty thousand years," says Twila Moon, a glaciologist at the National Snow and Ice Data Center. "We can decide we don't want to lose as much ice as quickly."

Antarctica

Ted Scambos has studied Antarctica for decades. But in December 2019, he saw the ice sheet's future with his own eyes.

He had just arrived at the remote shores of West Antarctica's Amundsen Sea, and his team had set up a field camp on the floating ice shelf that holds back Thwaites Glacier. Looking inland and uphill at the vast, frozen river that wends its way into the heart of West Antarctica, Scambos could see giant icy crevasses stretching across the horizon, like cracks in a wall on the brink of collapse.

"The sense of scale, of this huge region pushing towards the sea, actually gives one a feeling of unease," recalls Scambos, a glaciologist at the University of Colorado, Boulder. "You can feel the threat, live and in person."

Since the early 2000s, Thwaites, also known as the "Doomsday Glacier," has dumped a trillion tons of ice into the sea. Scientists like Scambos believe it may be in the early stages of an irreversible collapse, which could take out a large portion of the West Antarctic ice sheet, raising global sea levels by at least 2 feet, and perhaps more than 10.

A race is now on to determine whether Thwaites has already crossed such a tipping point, and whether some of the larger coastal glaciers rimming East Antarctica will be similarly imperiled if global warming continues unabated.

The edges of the shelf have a harder time holding back thicker floating ice, and so the entire glacier starts flowing faster into the sea. This triggers even more retreat in a runaway process known as the "marine ice sheet instability." According to Scambos, "That runaway situation may already be started at Thwaites." He adds that there are only "one or two regions left" where the bedrock rises and could potentially stabilize the glacier as it retreats inland.

The warm ocean water that's causing so much trouble for Thwaites is part of a deep, salty ring that encircles the continent. Today, a recent strengthening of the westerly winds that whip around Antarctica is pushing more of this warm water toward Thwaites where it can attack the underside of the glacier.

Even if we were to shut down all carbon emissions today, it's unlikely we could completely shut off the processes causing Thwaites to retreat: "It's just going to be a component of how the Earth works for the foreseeable future," Scambos says, "meaning millennia."

But not everyone is convinced that Thwaites is doomed. "I don't think we know enough to say we have reached a tipping point," says Indrani Das, a glaciologist at Columbia University. "Our observation period is not long enough to assess irreversibility."

What's more, even if a runaway scenario is underway, we can still slow it down by slashing emissions rapidly. Scambos notes that avoiding more than 2 degrees C (3.6 degrees F) of global warming could make a big difference. "It still runs away," he says, "but it's much slower."

While glaciologists have suspected for decades that Thwaites and the surrounding West Antarctic ice sheet are in a precarious position, East Antarctica's much larger and colder mantle of ice was long considered stable, at least by comparison. East Antarctica holds enough frozen water to lift sea levels up by 170 feet compared with West Antarctica's 16 feet. But over the past decade, the assumption that most of that ice will remain put has begun to fade, according to Howat, the Ohio State University glaciologist. Improved maps of the continent have revealed that large portions of East Antarctica, including major sections of the ice contained inside Totten and Denman glaciers and the Wilkes Basin, are also anchored on deep, reverse-sloping bedrock that may be prone to marine ice sheet instability.

While East Antarctica's deep-rooted glaciers "seem to be further away from reaching the tipping point for now," as Scambos puts it, continued ocean warming and circulation of warm, deep water beneath their protective ice shelves could eventually destabilize them. A 2014 modeling paper found that removing a comparably small "plug" of ice from the shelf buttressing the Wilkes Basin - equivalent to just 3 inches of sea-level rise - could be enough to tip off a runaway collapse that adds up to 13 feet to global sea levels. Recent airborne and satellite remote sensing surveys, meanwhile, reveal that both Totten and Denman Glaciers are already retreating at their grounding lines. The collapse of Totten would add the equivalent of another 13 feet of sea-level rise; Denman would add another 5.

"This accounts for a lot more sea level potential than West Antarctica," says Helen Fricker, a glaciologist at the Scripps Institution of Oceanography in San Diego, California.

As we go about our daily lives, the carbon-rich soils of the boreal forest and lush rainforests of the tropics are hard at work sucking up carbon dioxide, forming what are known as terrestrial carbon sinks. As a result, every year, land-based ecosystems absorb more CO2 than they emit. From 2007 to 2017, they removed about a third of total anthropogenic emissions from the atmosphere.

But three potential tipping points in the terrestrial system - one in the Arctic, one in the sub-Arctic, and another near the equator - could force the release of huge amounts of carbon stored within those sinks. Once those thresholds are passed, feedback loops might start spiraling, accelerating climate change and reshaping our planet's forests and soils.

Permafrost

In 2019, Brendan Rogers stumbled into an open wound of our warming planet. He was doing ecological fieldwork in the Alaskan tundra, during a summer so hot that he recalls people walking around in shorts and t-shirts. As he was about to set up a piece of equipment, the ground beneath his feet gave way, sending him falling into an empty crater.

Rogers had just walked into what scientists call a thermokarst feature. They're "landscape sloughs and slides, features all over the permafrost zone where the ground literally collapses." Formed by rapid melt, they are the fingerprints of a process taking place throughout the Arctic: permafrost thaw. Permafrost is ancient Arctic soil that usually stays frozen year-round (hence the "perma").

Historically, vast stores of permafrost in the northern Arctic regions of Alaska, Siberia, Canada, and Greenland have contributed to the Earth's carbon sink, taking in more carbon than they emit every year, thanks to the growth of carbon-eating lichens and mosses on the surface. But the effects of thaw might already have flipped the permafrost region from carbon sink to source. An international team of scientists estimated that during each winter from 2003 to 2017, Arctic permafrost regions lost 1.7 billion metric tons of carbon, while only storing an average of 1 billion metric tons of carbon each summer.

The National Oceanic and Atmospheric Administration's Arctic Report Card for 2019 found that the permafrost region has already started to lose more carbon than it captures - causing a net 300 to 600 million metric tons of carbon to be released into the atmosphere each year. (That's more than five times the emissions New York City generates in a year.) The data collected for the report card "has convinced me that this feedback has already started," says Ted Schuur, one of the report card's authors and a climate scientist at Northern Arizona University.

Over the next 300 years, worst-case scenario models predict that 208 billion metric tons of carbon could be released through gradual permafrost thaw, about 15 percent of what is currently stored. But it could also take place abruptly; sudden thaw in features like lakes, wetlands, and hills, which produce formations like the crater Rogers fell into, might lead to an additional 60 to 100 billion metric tons of CO2 emissions. That doesn't take into account more intense wildfires, which combust the carbon stored in permafrost soils and accelerate thaw. All these processes feed into an accelerating feedback loop triggering more warming and more permafrost loss.

One reason the loss of so much permafrost is so concerning to scientists is that it's irreversible. The carbon buried across the Arctic tundra took millennia to accumulate. Once it's gone, Lenton says, there's no getting it back.

Boreal forest

In the summer of 2014, the normally bright midday skies of Canada's Northwest Territories turned pitch black. After blood-red sun and weeks of thick smoke, Jennifer Baltzer watched as ash rained down over the little town of Yellowknife, where she lived and worked researching boreal forest ecosystems - a band of coniferous forest that circles the globe, right below the Arctic. That year hosted a particularly devastating wildfire season - the one road to Yellowknife was closed for three weeks, with no food coming in or out. For days, a huge cloud of smoke hung across the lake near where her family lived.

As Baltzer watched the forest burn from her home, with her kids sheltered inside, she was aware she was living in a region that is being reshaped by climate change. "The air quality was so bad that we couldn't take the kids outside," she recalls. "It was really hard to be outside. You actually felt physically ill."

The boreal forest spans 1.5 billion acres around the planet, more than half the area of Europe, spread across northern Russia and Canada. It's also the largest carbon storage reservoir on land, containing 30 to 40 percent of all carbon sequestered on land, and takes up slightly more carbon than it emits every year. Some of this carbon is kept above ground, in the trees, but a large chunk is invisible to the naked eye - about 85 percent of it is locked away in cold, wet soils. Over time, moss and slowly decomposing vegetation form layers of carbon-rich soil known as peat. In some regions where it's cold enough, the peat is largely permafrost.

But the boreal forests are changing. Fire is part of the natural rhythm of boreal forests, and many tree species within them are adapted to it. But as conditions become warmer and drier, wildfires are happening more frequently and burning over greater areas, threatening the vast reserves of carbon stored in the soils of the boreal region and potentially transforming the forest into grassland or tundra.

The 2014 wildfires in the Northwest Territories that Baltzer lived through burned 8.6 million acres of boreal forest that season alone (compared to the usual average of 1.5 million acres), releasing 94 million metric tons of CO2. The trend has only continued - the summer of 2020 was a record year for wildfires in Siberia, with 26.9 million acres of forest torched as temperatures reached over 100 degrees F in parts of the Arctic. As wildfires accelerate, researchers fear that carbon emissions from the fires could threaten the region's ability to store more carbon than it emits - and eventually, flip it to a source of carbon emissions.

The winter following the 2014 blazes, some fires were still smoldering in the soil, and Baltzer could see them popping up occasionally through the snow - a phenomenon known as "zombie fires." Her team studied the impacts of that wildfire season on carbon that had previously accumulated in soils, known as "legacy carbon." It found that the 2014 wildfires burned older and deeper carbon reserves, releasing them into the atmosphere.

That's one part of how the tipping point works in the boreal forest: As the climate warms, wildfires intensify, releasing more carbon, further accelerating warming, Baltzer explains. That's not the only feedback at play. As fires return more frequently, forests might fail to recover and slowly morph into grassland or tundra, reducing the amount of carbon stored aboveground. And as warming lures pests like bark beetles northward, it also threatens the well-being of the forests and the release of the carbon stored within them - another potential reinforcing loop.

There are other feedbacks, however, that could help stabilize the system. A study charting the regrowth of Alaskan forests following wildfires found that tree species in the region shifted from black spruce to deciduous trees - allowing the regenerated forests to store even more carbon than the old versions. That transition could mean that over time, the carbon impacts of forest fires could be less severe than previously believed. Baltzer says that similar transitions after fire could be taking place across the North American boreal region. These findings, she explains, "point to broader resilience of that particular function of the system."

Understanding how these different feedbacks might shape the future of the boreal forest and its vast reserve of carbon is a massive scientific undertaking. Scott Goetz is the leader of NASA's Arctic-Boreal Vulnerability Experiment, a group of scientists keeping tabs on the vital signs of the region, monitoring, among other things, shifts in how the forests are storing and releasing carbon. His team uses field measurements, data from aircraft flown over the forest, and satellites to paint a picture of how much carbon boreal forests take up and releases every year. Those measurements then inform models of the region's future.

Goetz says that in many ways the multiple feedbacks at play make predicting what will happen "a hellishly complicated problem." Because of this, Goetz says he doesn't have a clear answer about if, when, and how fast the system could cross a tipping threshold. "I don't think we actually know."

Amazon rainforest

David Lapola has worked in the Amazon rainforest for many years, but September of 2015 sticks out in his memory. He was teaching a field course at a research station some 40 miles north of Manaus, in the center of the Amazon basin. That month was extremely hot and dry, and Lapola noticed how it had sucked the moisture out of the forest. He recalls that the top 20 inches or so of the soil was bone dry - and this was in the central Amazon, the world's largest rainforest, which normally gets almost 10 feet of rain every year.

"I've never seen it like that, neither before nor later on," Lapola says. "I remember seedlings drying out and dying, small saplings getting drier, the leaves browning."

Lapola was witnessing first-hand the impacts of a devastating El Niño - a naturally occurring climate pattern, worsened by global warming, that brought unusually dry and hot conditions to the Amazon that year. El Niño-fueled droughts kill trees and suppress growth across the Amazon. Dead trees then release the carbon stored within them, and decreased tree growth means less carbon stored across the system as a whole. The result: The 2015 El Niño drought temporarily turned rainforests from carbon sinks into carbon sources, adding about 2.5 billion tons of carbon to the atmosphere.

That could be a preview of what's to come. The Amazon rainforest, known commonly as the lungs of the world, holds an estimated 150 to 200 billion metric tons of carbon in its vast reserves of tree and plant mass. Historically, it has represented around a quarter of the world's terrestrial carbon sink. But the Amazon, like so many other places on Earth, is getting hotter and drier. Over the past century, the temperature in the region has risen by 1 to 1.5 degrees C (1.8 to 2.7 degrees F), and in some places, the dry season has lengthened from four to nearly five months.

All this has affected what Lapola calls tree demography - how long trees live, their mortality rates, and the growth of new trees. Though higher levels of CO2 in the atmosphere have caused tropical trees to take up more of the greenhouse gas through photosynthesis, an effect known as "carbon fertilization," the Amazon carbon sink declined by a third from 2005 to 2015 when compared to the 1990s, mostly a result of increased tree mortality, and a fifth now acts as a carbon source. Now, some models predict that the Amazon will become a permanent source of carbon emissions by 2035, further contributing to climate change.

Climate change isn't the only factor that might push the Amazon toward a tipping point; deforestation also plays a role. Cattle ranchers and farmers have been cutting down large swaths of the rainforest, carving out a portion roughly the size of Connecticut last year. Much of the moisture in the Amazon comes from the trees themselves. They suck up water from the soil through their trunks - like liquid through a straw - and exhale it into the atmosphere through little pores on the undersides of leaves in a process known as transpiration. Transpiration cools the rainforest and produces rainfall. So if the forest is cut down, the surrounding area dries out.

In 2018, Thomas Lovejoy, an environmental scientist at George Mason University in Virginia, and Carlos Nobre, a senior scientist at the Institute of Advanced Studies at the University of São Paulo in Brazil, raised the alarm, estimating that if 20 to 25 percent is deforested, a tipping threshold may be crossed, transforming the Amazon into a savanna. That's an alarming estimate, given that 15 to 17 percent of the Amazon has already disappeared, with Brazil under nationalist leader Jair Bolsonaro leading tropical forest losses worldwide in 2019. The country led the world in losing tropical forest again in 2020. Lapola says that in the Amazon, "deforestation comes together with global climate" and threatens to push the region past a dangerous tipping point, a risk not just for the health of the rainforest but for the whole planet.

What can we do?

As coral reefs dissolve, Antarctica melts, and vast swaths of rainforest disappear, the world already seems to be headed down a dark path: 2 or 3 degrees C (3.6 or 5.4 degrees F) of warming; land, sea, and ice fundamentally transformed; and the consequences playing out on coastlines and in city neighborhoods thousands of miles away.

But Jacquelyn Gill, the University of Maine paleoclimatologist, does worry that too much focus on tipping points could backfire. It's a sentiment echoed by the glaciologist Twila Moon. Tipping points are so scary that they could feed into a narrative of hopelessness. "We may not be able to predict exactly when some of these tipping points occur, but what we can do is control our actions, take ownership of our emissions," Gill says.

And there are reasons for optimism. A few researchers have begun to study another set of tipping points - a group that, instead of spiraling the planet into an increasingly dangerous state, could help shift it back into balance. These so-called "social tipping points" follow the same basic principle as their counterparts in the natural world: First, change happens slowly, then all at once.

In 1907, some 140,000 Americans had a registered automobile; others got around cities by horse-drawn vehicles, bicycles, and trolley cars. By 1917, however, thanks to plummeting price tags for automobiles, there were almost 5 million cars on American roads. A more recent example: In 2003, no state in the country legally recognized gay marriage. Twelve years later, after a dramatic shift in public opinion and a ruling by the Supreme Court, same-sex marriage was legal in all 50.

"Fast change can happen," says Ilona Otto, a researcher at the Potsdam Institute for Climate Impact Research in Germany. Otto and 13 other scientists released a paper last year arguing that several such social tipping points could drive a rapid increase in initiatives aimed at cutting carbon dioxide emissions. Some of them are concrete and obvious - a drop in renewable energy prices, for example, such that solar and wind are cheaper than fossil fuels. Others are more abstract, like a shift in public attitudes toward seeing fossil fuels as fundamentally immoral.

Most social tipping points are hard to measure, and even harder to predict. But there are signs that they may be slowly approaching. In 2009, a new solar farm cost 223 percent more than a new coal plant. Today, those numbers have roughly flipped. That means that one of Otto and her colleagues' key thresholds is within reach: In many regions, renewables are now a cheaper source of energy than fossil fuels.

At the same time, the movement to divest university endowments from fossil fuels, combined with high-profile climate protests by Swedish activist Greta Thunberg and organizing by other young people, has already contributed to a growing sense, especially among younger millennials and Generation Z, that fossil fuel use is unethical. Some people have begun to avoid flying due to "flygskam," or "flight shame," over the airline industry's sky-high carbon footprint; even oil and gas giants now feel the need to advertise their promises to bring their emissions to zero by 2050. In the U.S., youth activism sparked a conversation - and then a movement - around the idea of a clean energy-focused Green New Deal.

It's hard to say whether these trends will continue. But they provide reason to hope that we'll hit these more virtuous tipping points before the catastrophic ones. "Hopefully, these tipping points will start to accumulate," Otto says, "and then come together as an avalanche."

This story was reported and written by Alexandria Herr, Shannon Osaka, and Maddie Stone. Videos were produced by Daniel Penner and Jesse Nichols. Jacky Myint handled design and development. Teresa Chin led the art direction. Illustration was done by K. Amelia Bates. Jacob Banas, Mignon Khargie, Myrka Moreno, and Christian Skotte did promotion and additional production.

This project was edited by Katherine Bagley, Matt Craft, Maddie Stone, and Nikhil Swaminathan. It was copy edited by Kate Yoder and fact checked by Ysabelle Kempe.

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The 7 climate tipping points that could change the world forever - Grist

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In 2019 an international team of scientists published a commentary in the celebrated science journal Nature, sounding the alarm of a planet in crisis - and calling for transformative change. "We are in a state of planetary emergency," they wrote, departing from the usual sterility of scientific writing.

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'We deserve to be taught about it': why students want climate crisis classes | Education | The Guardian

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'We deserve to be taught about it': why students want climate crisis classes | Education | The Guardian

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n five years' time, every student at Sheffield University - whether they study maths, music or drama - will also need to get to grips with sustainability. Be it the climate crisis, global poverty or gender inequality, every course will examine some of the major challenges the world faces.

"It isn't about making musicians into climate scientists," insists sustainability manager James Merryclough. "This is responding to what our students want and this generation is looking for. We know employers will want these skills too. They'll want students who understand global challenges, and the macro environment of where they fit into the world."

Rather than compulsory climate crisis lectures, each academic department will reimagine their curriculums through a sustainable lens. Last year, for example, landscaping students took an in-depth look at the climate drivers behind increased flooding on the East Yorkshire coast, and examined how better planning could reduce risk. Similarly, the university is currently looking at how arts and humanities students can collaborate with scientists, using their skills in words and music to come up with more compelling ways to talk to the public about the global challenges we face.

Sheffield's initiative is one of many major changes being implemented across UK universities, in response to a student-led campaign to address what campaigners say is a gaping hole across higher education.

This is borne out in a survey of 16-18 year olds published this month by the University of Winchester, which showed that although 54% see climate breakdown as the second biggest threat to the UK (after the quality of the NHS), less than half (46%) rated universities as doing a good job of addressing it.

It's no longer enough to limit an education on sustainability to those undergraduates who opt for geography or environmental sciences, says Quinn Runkle, director of education at SOS-UK, the sustainability arm of NUS. "It shouldn't be down to that small proportion of students. This should be a learning entitlement."

That was the conclusion Teach the Future founder Joe Brindle came to back in 2019. As he embarked on his final year of college a 17-year-old Brindle, who had organised school climate strikes, realised none of what he'd learned had come via his formal education.

"Climate breakdown will greatly determine the future of me and my peers, but we haven't been prepared for it at all," he says. "It feels like education is failing if it's not preparing us for our future."

His research has found that just 4% of students feel well-informed about the climate crisis, but 68% say they want to learn more.

In October last year, Brindle travelled to London with his mum, a teacher, to the National Education Union's (NEU) climate emergency conference. There, in front of hundreds of teachers, students and parents, he formally launched Teach the Future, setting out his plan for an overhaul of education at both schools and universities. "They instantly saw that what we were asking for was really important," he says.

What Teach the Future is asking for is threefold: a review by the Department of Education into whether current teaching on the climate crisis is good enough ("we're pretty sure the conclusion will be no," says Brindle), for all teacher training to include mandatory lessons on sustainability, and - most significant of all - for the implementation of the Climate Emergency Education Bill, a draft bill submitted in February which includes a requirement for all education providers to teach students about the climate crisis.

"It isn't only the right thing to do for the planet," insists Brindle. "It's the right thing for students. Whatever job you go into - whether a farmer, a builder or a banker - you're going to need to understand the climate crisis in this modern world."

Some universities are already taking this message on board. As part of its new carbon neutral plan - which saw beef banned from campus outlets and divestment from fossil fuels - Goldsmiths has committed to "greening" its curriculum by 2021. Its new MA in art and ecology will teach artists to express ideas around climate breakdown, pollution and biodiversity loss in their creative work.

At the University of Winchester, trainee teachers will, from this year, have the option of enrolling in a dedicated course, the first in the UK (and, say Winchester, the world) to equip teachers with accredited skills on climate change. All undergraduates will be able to study activism as an optional module, and all campus policies must cover climate breakdown.

"The world we live in is changing rapidly around us and many organisations are sleep-walking into crisis," says Joy Carter, Winchester's vice-chancellor and co-chair of the UK Commission for Climate for Further and Higher Education. "It's so important that students are prepared - prepared for what lies ahead, but also prepared to make a difference in the world and change what they can for good. It's the most important mission for any educational establishment to tackle."

Other universities are overhauling course content. Keele University has transformed its geology course, says Zoe Robinson, the university's first director of sustainable education. "It was traditionally focused on the oil and gas industry," she says, with some initial pushback from the department at the idea of taking a more sustainable approach. "But now we're in a position where the programme has been mapped against the UN's Sustainability Development goals and [the department] are talking about a decarbonisation of the curriculum. We've seen a complete turnaround from some initial suspicion to wanting to make a mark in their discipline."

Despite signs that some universities are taking steps in the right direction, campaigners argue too many are still failing to recognise that sustainability should be as essential as maths, English or science.

"We're asking for students to be exposed to the breadth of thinking and given the respect as learners to decide for themselves what aligns with their values, their world views and their future professions, as opposed to being fed one particular approach," says Runkle.

To get there SOS UK is working with examination and accreditation bodies and encouraging universities to give academics the time to explore how they can best teach students, of whatever discipline, about the climate crisis.

"My generation and the generations to come are going to grow up in a world greatly affected by climate breakdown," says Brindle. "That's going to be the key defining issue of our adulthood. And we deserve to be taught about that."

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'We deserve to be taught about it': why students want climate crisis classes

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n five years' time, every student at Sheffield University - whether they study maths, music or drama - will also need to get to grips with sustainability. Be it the climate crisis, global poverty or gender inequality, every course will examine some of the major challenges the world faces.

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Fifth of countries at risk of ecosystem collapse, analysis finds | Environment | The Guardian

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Fifth of countries at risk of ecosystem collapse, analysis finds | Environment | The Guardian

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One-fifth of the world's countries are at risk of their ecosystems collapsing because of the destruction of wildlife and their habitats, according to an analysis by the insurance firm Swiss Re.

Natural "services" such as food, clean water and air, and flood protection have already been damaged by human activity.

More than half of global GDP - $42tn (£32tn) - depends on high-functioning biodiversity, according to the report, but the risk of tipping points is growing.

Countries including Australia, Israel and South Africa rank near the top of Swiss Re's index of risk to biodiversity and ecosystem services, with India, Spain and Belgium also highlighted. Countries with fragile ecosystems and large farming sectors, such as Pakistan and Nigeria, are also flagged up.

Countries including Brazil and Indonesia had large areas of intact ecosystems but had a strong economic dependence on natural resources, which showed the importance of protecting their wild places, Swiss Re said.

"A staggering fifth of countries globally are at risk of their ecosystems collapsing due to a decline in biodiversity and related beneficial services," said Swiss Re, one of the world's biggest reinsurers and a linchpin of the global insurance industry.

"If the ecosystem service decline goes on [in countries at risk], you would see then scarcities unfolding even more strongly, up to tipping points," said Oliver Schelske, lead author of the research.

Jeffrey Bohn, Swiss Re's chief research officer, said: "This is the first index to our knowledge that pulls together indicators of biodiversity and ecosystems to cross-compare around the world, and then specifically link back to the economies of those locations."

The index was designed to help insurers assess ecosystem risks when setting premiums for businesses but Bohn said it could have a wider use as it "allows businesses and governments to factor biodiversity and ecosystems into their economic decision-making".

The UN revealed in September that the world's governments failed to meet a single target to stem biodiversity losses in the last decade, while leading scientists warned in 2019 that human s w ere in jeopardy from the accelerating decline of the Earth's natural life-support systems. More than 60 national leaders recently pledged to end the destruction.

The Swiss Re index is built on 10 key ecosystem services identified by the world's scientists and uses scientific data to map the state of these services at a resolution of one square kilometre across the world's land. The services include provision of clean water and air, food, timber, pollination, fertile soil, erosion control, and coastal protection, as well as a measure of habitat intactness.

Those countries with more than 30% of their area found to have fragile ecosystems were deemed to be at risk of those ecosystems collapsing. Just one in seven countries had intact ecosystems covering more than 30% of their country area.

Among the G20 leading economies, South Africa and Australia were seen as being most at risk, with China 7th, the US 9th and the UK 16th.

Alexander Pfaff, a professor of public policy, economics and environment at Duke University in the US, said: "Societies, from local to global, can do much better when we not only acknowledge the importance of contributions from nature - as this index is doing - but also take that into account in our actions, private and public."

Pfaff said it was important to note that the economic impacts of the degradation of nature began well before ecosystem collapse, adding: "Naming a problem may well be half the solution, [but] the other half is taking action."

Swiss Re said developing and developed countries were at risk from biodiversity loss. Water scarcity, for example, could damage manufacturing sectors, properties and supply chains.

Bohn said about 75% of global assets were not insured, partly because of insufficient data. He said the index could help quantify risks such as crops losses and flooding.

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Fifth of countries at risk of ecosystem collapse, analysis finds

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One-fifth of the world's countries are at risk of their ecosystems collapsing because of the destruction of wildlife and their habitats, according to an analysis by the insurance firm Swiss Re. Natural "services" such as food, clean water and air, and flood protection have already been damaged by human activity.

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Unless the world begins to rapidly reduce greenhouse gas emissions the 1.5C goal of the Paris Agreement "will slip out of reach," according to the latest UN Environment Programme (UNEP) emissions gap report.

The annual report, now in its 10th year, provides a "bleak" assessment of the ever-growing gap between actual emission reduction commitments by countries and those necessary to achieve the goals of the Paris Agreement: to limit warming to "well-below 2C above preindustrial levels" and pursue efforts to limit the temperature increase to 1.5C.

Global CO2 emissions have increased by around 11% since the first UNEP emissions gap report in 2010. Each year of growing global emissions means that deeper and faster cuts are needed to meet the Paris Agreement targets, and increases the amount of CO2 that would need to be removed from the atmosphere through negative emissions to make the 1.5C target viable.

The 2019 emission gap report suggests that there is no sign of GHG emissions peaking in the next few years. Even if countries meet their existing climate pledges ( nationally determined contributions, NDCs) emissions will continue to rise modestly over the next decade, it says. By 2030, the UNEP report estimates that emissions will be 27% and 38% higher than is needed to limit warming to 2C and 1.5C, respectively.

At the same time, there have been some positive developments over the past decade, UNEP notes. Many countries have enacted climate policies, though with differing levels of ambition. Clean energy technologies have fallen in cost as they are deployed at an increasing scale.

This means that while global emissions are still far too high to keep warming well-below 2C, very high emission outcomes with 4C or more warming are also increasingly less likely.

Far from sufficient

UNEP's annual emission gap report examines the difference between the actions that countries have committed to take and what would be needed to meet agreed-upon climate goals. (Carbon Brief's archives also include detailed coverage of the UNEP reports in 2014, 2015, 2016, 2017 and 2018.)

The figure below, adapted from the report, shows emission trajectories associated with policies that were in place in 2005 - but nothing after that point - in red and current policies already implemented by governments in orange.

Additional commitments in NDCs that are not yet implemented are shown in yellow for unconditional commitments and light blue for those conditional on aid or action by other countries. Emission trajectories consistent with staying below 2C, 1.8C and avoiding 1.5C are shown in blue, purple and grey, respectively.

Median emission scenarios adapted from figure 3.1 in the UNEP Emission Gap Report 2019. Red line shows a scenario with no new climate policies after 2005, orange shows existing policies already implemented by governments, yellow and light blue lines show additional conditional and unconditional NDCs, blue line shows emissions consistent with a below 2C trajectory, purple line below 1.8C, and grey line shows emissions consistent with a 1.5C trajectory. Chart by Carbon Brief using Highcharts.

There is a large gap between what countries have committed to, in terms of future emission reductions, and what would be needed to meet the Paris Agreement targets. Current NDCs would leave global emissions in 2030 some 12-15bn tonnes of CO2 (GtCO2) short of what is needed to put the world on track to limit warming below 2C, and 29-32GtCO2 short for 1.5C.

While Paris NDCs get the world a small part of the way towards a 2C trajectory, there is no guarantee that even existing Paris commitments will be met, to say nothing of being strengthened. (Countries are due to " communicate or update" their pledges by 2020, under the " ratchet mechanism" of the Paris deal.)

The UNEP report points out that seven large countries are clearly not on track to meet their Paris Agreement commitments: Australia, Brazil, Canada, Japan, South Korea, South Africa and the US.

At the same time, it notes that an increasing number of countries have set net-zero emission targets. Some 65 countries and 10 major regions have committed to net-zero emissions by 2050. However, these only include five members of the G20 group of major economies and only two of these - the UK and France - have passed binding legislation so far.

The 2019 UNEP report features a new 1.8C scenario for the first time, in addition to the below-2C and 1.5C emission trajectories featured in prior reports. This is, in part, because there is a desire to explore outcomes between 1.5C and 2C, as the steady rise in global CO2 emissions puts 1.5C increasingly out of reach.

Time running out for 1.5C

There is relatively little carbon budget remaining for warming to be limited to 1.5C. With 2019 emissions widely expected to be similar to those in 2018, there will be only around 340GtCO2 - or 8 years of current emissions - remaining, that can be emitted before the world passes 1.5C warming.

While this carbon budget can be expanded through the widespread use of negative emissions technologies (NETs) later in the century - as occurs in the 1.5C scenarios used by the UNEP report - there is some reluctance to bet the future on NETs that are largely unproven at scale today.

The figure below, adapted from one created by CICERO's Dr Robbie Andrews, shows emission trajectories to limit warming to below 1.5C in the absence of net-negative emissions. The different lines show the emissions reductions that would be required if emissions had peaked in each year, between 2000 and 2026, with the current year (2019) highlighted in grey.

Emission reduction trajectories associated with limiting warming below 1.5C by starting year. Solid black line shows historical emissions, while dashed black line shows emissions constant at 2018 levels. Source: Historical CO2 emissions from the Global Carbon Project. 1.5C carbon budgets based on the IPCC SR15 report. Original figure from Robbie Andrews. Chart by Carbon Brief using Highcharts.

If emissions had peaked and begun to decline after the year 2000, the 1.5C target would have been much easier to achieve, only requiring reductions of around 3% per year. By contrast, limiting warming to below 1.5C starting in 2019, without net-negative emissions, would require a 15% cut each year through to 2040.

If emissions continue at current levels for another few years, then the only way to limit warming to below 1.5C in the absence of net-negative emissions would be to immediately cut all global emissions to zero.

Each year that passes without global emission reductions puts the 1.5C target further out of reach. While the below-2C target is easier to achieve than 1.5C, delays will make it increasingly difficult, too. The figure below shows the emission reductions needed, by peaking year, to meet the 2C target without use of net-negative emissions.

Emission reduction trajectories associated with limiting warming below 2C without net-negative emissions, by starting year. Solid black line shows historical emissions, while dashed black line shows emissions constant at 2018 levels. Source: Historical CO2 emissions from the Global Carbon Project. Below-2C carbon budgets based on the IPCC SR15 report. Original figure from Robbie Andrews. Chart by Carbon Brief using Highcharts.

If global emissions had peaked in the year 2000, they would have had to decline at a gradual 1-2% per year to limit warming below 2C by 2100. A more difficult - but still achievable - rate of around 4% to 5% per year would be needed if emissions peak and start to decline after 2019. However, if reductions are delayed for another decade, meeting the 2C target becomes much more challenging, requiring emissions to fall by 7% per year.

Moving away from business as usual

While the UNEP report makes it clear that emissions are far from on track to meet the Paris Agreement goals, it does contain some positive news. The climate policies enacted by countries and the falling price of clean energy technologies have made some of the worst-case emissions outcomes considerably less likely, it says.

The UNEP report projects that current policies will move emissions substantially lower than most of the Intergovernmental Panel on Climate Change (IPCC) scenarios examining potential outcomes in the absence of any action to tackle climate change, so-called "no-policy baseline" pathways.

It puts emissions in 2030 at 60GtCO2e, somewhere between SSP2-4.5 (57GtCO2e) and SSP3-6.0 (62GtCO2e), but well below SSP3-7.0 (69GtCO2e) and the worst-case SSP5-8.5 (71GtCO2e).

This follows similar estimates from the 2019 IEA World Energy Outlook, which suggested that stated plans and policies would lead to emissions lower than most IPCC baseline no-policy scenarios over the next few decades.

This is a really important figure. The IEA suggests that falling costs of clean energy make it likely that emissions will be at or below RCP4.5 levels in 2040, even in the absence of any new policies. Its not enough, but it makes worst-case outcomes far less likely (via @jritch) pic.twitter.com/w6nAyMP9bd
- Zeke Hausfather (@hausfath) November 18, 2019

The UNEP report suggests that even if all unconditional NDCs under the Paris Agreement are implemented, the world is still on track for a warming of around 3.2C above pre-industrial levels in the year 2100. While this is far from a desirable outcome, it is substantially better than the 4.6C in the worst-case no-policy emission scenario.

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UNEP: 1.5C climate target 'slipping out of reach' | Carbon Brief

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Unless the world begins to rapidly reduce greenhouse gas emissions the 1.5C goal of the Paris Agreement "will slip out of reach," according to the latest UN Environment Programme (UNEP) emissions gap report.

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Have you always wanted to bring environment into your language classroom but not always been sure how to do it? Then this course is for you.

Maybe you have used lessons from this site. Why not investigate the best ways for you to bring sustainability into the language class as you learn with other like-minded participants and course tutor Owain, publisher of eltsustainable and experienced online tutor and materials developer.

Enrol for the next course below. At $6.00 it is excellent value and includes a great deal of moderator attention, a great learning methodology based on constructivist and connectivist principles and a highly-experienced tutor. It includes a certificate of completion too.

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E-learning course: Language Teaching for the Planet

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Have you always wanted to bring environment into your language classroom but not always been sure how to do it? Then this course is for you. Maybe you have used lessons from this site. Why not investigate the best ways for you to bring sustainability into the language class as you learn with other like-minded...

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Could teachers be the climate game changers?

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Schools must empower them to embrace their roles as teachers of climate change and climate justice.

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Swedish climate activist Greta Thunberg stands aboard the catamaran La Vagabonde as she sets sail to ... [+]
AFP via Getty Images

The climate movement has been riven lately by a debate pitting individual lifestyle change against systemic change, as if the two compete.

Many experts contend both are needed, and new research links them even more closely. The public is more likely to support systemic action, the study finds, if those advocating it have a low carbon footprint.

"It is really important that scientists, or other messengers who communicate with the public, model those behaviors that reduce carbon emissions to drive their point home," one of the authors, Professor Elke Weber, said in an interview released yesterday by Princeton University.

"Our new research showed that the carbon footprints of those communicating the science not only affects their credibility, but also affects audience support for the public policies for which the communicators advocated," said Weber, the associate director for education at Princeton's Andlinger Center for Energy and the Environment.

The study, titled " Climate change communicators' carbon footprints affect their audience's policy support," may explain why Greta Thunberg has succeeded more than others at communicating the climate crisis and galvanizing social action. Thunberg has insisted on individual change-and modeled it-while advocating systemic change.

"The implications of these results are stark," the authors write in the journal Climatic Change. "Effective communication of climate science and advocacy of both individual behavior change and public policy interventions are greatly helped when advocates lead the way by reducing their own carbon footprint."

Recently Pennsylvania State University climate scientist Michael Mann warned that climate denialists are exploiting calls for individual action to distract from the need for systemic change. Some writers interpreted this argument to pit Mann against Thunberg, but in fact, Mann, an ardent supporter of Thunberg, merely argued that individual action cannot replace systemic.

Some, however, are waiting for systemic to replace individual. Axios energy reporter Amy Harder recently confessed her carbon footprint and suggested she would not reduce it before systemic change occurs.

"I'm not losing sleep over my flying and eating habits," she writes, arguing governments must enact economic policies to change those habits, "and I'll only make big changes if the price tags get a lot bigger."

This study suggests Harder undermines her work's message:

"We find that people are more likely to support policies if the advocate for these policies has a low carbon footprint," they write. "Our new finding is that their carbon footprint also affects audience support for public policies advocated by the communicator."

But it's not too late, the researchers point out, for Harder to boost her impact by flying less and eating less meat:

"In a second study, we show that the negative effects of a large carbon footprint on credibility are greatly reduced if the communicator reforms their behavior by reducing their personal carbon footprints."

Led by Shahzeen Z. Attari at Indiana University, the researchers presented 3,600 participants with one of six policy proposals:

1. Regulate CO₂ emissions

2. Tax CO₂ emissions

3. Increase generation of nuclear power

4. Stabilize human population

5. Increase renewable energy

6. Enhance infrastructure for public transit

Initially the participants expressed support for each policy. They favored increasing renewable energy the most and stabilizing human population the least, but support for all six began neutral or higher.

Then the researchers described the advocates of these proposals as having either a high or low carbon footprint, based on home energy use, and again assessed participants' support.

"High personal home energy use not only reduces researcher credibility," they found, "but also reduces support for the policy advocated by the researcher."

The study has implications for advocates and communicators in general.

"Advocates for energy conservation and for policies that reduce carbon emissions must expect ad hominem arguments based on their own energy use. Such arguments are probably best countered personally, by leading the way and demonstrating how to act in concordance with one's own beliefs and recommendations, and by being an exemplar others can follow, rather than relying primarily on communicating scientific facts about global warming and its risks."

No One Seemed To Notice Greta Thunberg's Critique Of The Green New Deal

... Read More

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Greta Is Right: Study Shows Individual Lifestyle Change Boosts Systemic Climate Action

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The climate movement has been riven lately by a debate pitting individual lifestyle change against systemic change, as if the two compete. Many experts contend both are needed, and new research links them even more closely. The public is more likely to support systemic action, the study finds, if those advocating it have a low carbon footprint.

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Italy makes climate awareness compulsory

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Italy makes climate awareness compulsory

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Public schools will require children in every grade to study sustainability. That could put Italy at the forefront of environmental education.

A student demonstration in September in Rome demanding action on climate change. Credit... Massimo Percossi/ANSA, via Associated Press

ROME - Yes, children, climate change will be on the test.

Italy's education minister said Tuesday that its public schools would soon require students in every grade to study climate change and sustainability, a step he said would put Italy at the forefront of environmental education worldwide.

The lessons, at first taught as part of the students' civics education, will eventually become integrated throughout a variety of subjects - a sort of "Trojan horse" that will "infiltrate" all courses, the education minister, Lorenzo Fioramonti, said.

Environmental advocates welcomed the new subject matter, with some caveats.

Teaching children about sustainability is "certainly very important" said Edoardo Zanchini, vice president of Legambiente, Italy's leading environmental group. But he warned that responsibility should not simply be passed on to children.

"Science tells us the next 10 years are crucial," he said. "We cannot wait for the next generation."

Mr. Fioramonti is a member of the anti-establishment Five Star Movement, which has long put environmental concerns at the heart of its identity. He has already become a target of conservatives for backing taxes on sugar and plastics, and for encouraging students to take part in climate protests last September instead of attending class.

Starting in September 2020, he said, teachers in every grade will lead lessons in climate change and environmental sustainability. That 33-hour-a-year lesson, he said, will be used as a pilot program to ultimately fold the climate agenda of the United Nations into the entire curriculum.

So merely studying place names and locations in geography class? "Forget that," Mr. Fioramonti said. Geography courses will soon study the impact of human actions on different parts of the planet, too, he said.

In an interview, Mr. Fioramonti said that a group of experts - including Jeffrey D. Sachs, director of the Harvard Institute for International Development, and Kate Raworth of Oxford University's Environmental Change Institute - will act as "peer reviewers" for ministry staff preparing the curriculum. By January, he said, the ministry will be ready to train teachers.

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Merely studying place names and locations in geography class? "Forget that," Education Minister Lorenzo Fioramonti said Tuesday. Credit... Remo Casilli/Reuters

For children age 6 to 11, he said, "we are thinking of using the fairy-tale model," in which stories from different cultures would emphasize a connection to the environment. Middle schoolers would be expected to learn more technical information, and high school students would explore the United Nations' 2030 Agenda for Sustainable Development in depth.

Until August, Five Star had governed Italy for more than a year with the nationalist League party, led by Matteo Salvini, who is still the country's most popular politician, and who has a skeptical view of climate change.

One cold spring day in Milan, Mr. Salvini, then the interior minister, appeared to trivialize climate change.

"Talking about global warming - we are in the middle of May and call upon global warming, because we haven't had a cold like this in Italy in recent years," he said. "We are turning on our heaters."

Mr. Fioramonti suggested that Mr. Salvini needed to be educated.

"That's the kind of nonsense we want to avoid by educating children that this is the most important challenge humanity has ever faced," he said. "And I want to secure this before there is any change in government that can imperil that kind of process."

But Mr. Salvini still looms over the wobbly Five-Star-led government, and Italy's many government collapses in recent years have cut short other educational programs. An attempt by a left-leaning government to teach children how to spot disinformation, for example, was discontinued after it lost power.

Mr. Fioramonti said a law passed last year, when Five Star was still aligned with the League, gave him the authority to introduce lessons on climate change. He said that the conditions had not been right to go forward with the new curriculum then, but that they were now.

Still, many Italians are concerned that Five Star's emphasis on environmental issues - or, perhaps, its failure to pursue such goals competently - is destroying the country's economy.

This month, Italy faced a new economic emergency when the foreign operator of a southern Italian steel plant, Ilva, said it would pull out because the Five Star-led government had decided to end criminal immunity for environmental breaches even as the company sought to clean up the polluted facilities. Such a move could cost Italy more than 8,000 jobs.

One environmental activist expressed reservations that Mr. Fioramonti's plan may be too dogmatic.

Chicco Testa, president of the environmental group Assombiente, urged officials to make sure children were exposed to varied views, including those who claim that climate change is not primarily caused by man. "To listen to people who say different things is good," he said. "What the U.N. says is not gospel."

But as President Trump began pulling the United States out of the landmark Paris Agreement this week, Mr. Fioramonti said that every country needed to do its part to stop the "Trumps of the world" and that his ambition was to show children there was another way.

"The 21st century citizen," he said, "must be a sustainable citizen."

Anna Momigliano contributed reporting.

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Italy's Students Will Get a Lesson in Climate Change. Many Lessons, in Fact.

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Public schools will require children in every grade to study sustainability. That could put Italy at the forefront of environmental education. ROME - Yes, children, climate change will be on the test. Italy's education minister said Tuesday that its public schools would soon require students in every grade to study climate change and sustainability, a step he said would put Italy at the forefront of environmental education worldwide.

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Dynamic maps of sea level rise. Will global warming affect you?

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Social tipping dynamics for stabilizing Earth’s climate

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Social tipping dynamics for stabilizing Earth’s climate

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, Jonathan F. Donges, , Avit Bhowmik, Richard J. Hewitt, Wolfgang Lucht, Johan Rockström, Franziska Allerberger, Mark McCaffrey, Sylvanus S. P. Doe, Alex Lenferna, Nerea Morán, Detlef P. van Vuuren, and Hans Joachim Schellnhuber

Contributed by Hans Joachim Schellnhuber, November 15, 2019 (sent for review January 22, 2019; reviewed by J. David Tabara and Jessika E. Trancik)

This article has a Letter. Please see:

Significance

Achieving a rapid global decarbonization to stabilize the climate critically depends on activating contagious and fast-spreading processes of social and technological change within the next few years. Drawing on expert elicitation, an expert workshop, and a review of literature, which provides a comprehensive analysis on this topic, we propose concrete interventions to induce positive social tipping dynamics and a rapid global transformation to carbon-neutral societies. These social tipping interventions comprise removing fossil-fuel subsidies and incentivizing decentralized energy generation, building carbon-neutral cities, divesting from assets linked to fossil fuels, revealing the moral implications of fossil fuels, strengthening climate education and engagement, and disclosing greenhouse gas emissions information.

Abstract

Safely achieving the goals of the Paris Climate Agreement requires a worldwide transformation to carbon-neutral societies within the next 30 y. Accelerated technological progress and policy implementations are required to deliver emissions reductions at rates sufficiently fast to avoid crossing dangerous tipping points in the Earth's climate system. Here, we discuss and evaluate the potential of social tipping interventions (STIs) that can activate contagious processes of rapidly spreading technologies, behaviors, social norms, and structural reorganization within their functional domains that we refer to as social tipping elements (STEs). STEs are subdomains of the planetary socioeconomic system where the required disruptive change may take place and lead to a sufficiently fast reduction in anthropogenic greenhouse gas emissions. The results are based on online expert elicitation, a subsequent expert workshop, and a literature review. The STIs that could trigger the tipping of STE subsystems include 1) removing fossil-fuel subsidies and incentivizing decentralized energy generation (STE1, energy production and storage systems), 2) building carbon-neutral cities (STE2, human settlements), 3) divesting from assets linked to fossil fuels (STE3, financial markets), 4) revealing the moral implications of fossil fuels (STE4, norms and value systems), 5) strengthening climate education and engagement (STE5, education system), and 6) disclosing information on greenhouse gas emissions (STE6, information feedbacks). Our research reveals important areas of focus for larger-scale empirical and modeling efforts to better understand the potentials of harnessing social tipping dynamics for climate change mitigation.

Preventing dangerous climate change and its devastating consequences is a defining task for humanity ( 1, 2). It is also an indispensable prerequisite for achieving sustainable development ( 3, 4). Limiting global warming to 1.5 °C as stipulated in the Paris Climate Agreement ( 5) scientifically implies a complete net decarbonization of the world's energy and transport systems, industrial production, and land use by the middle of this century. In their "roadmap for rapid decarbonization," Rockström et al. ( 6) highlight that rapid increase of the share of zero-carbon energy within the global energy system would be needed to achieve this objective, likely alongside a considerable strengthening of terrestrial carbon sinks. In one scenario, the zero-carbon share of the energy system doubles every 5 to 7 y for the next several decades ( 6). Carbon emissions that are currently still on the rise at rates of 0 to 2% per year, despite decades-long efforts in international climate negotiations, would thereby need to pivot to a rapid decline of ultimately 7% per year and more. These emission reduction rates would surpass by far even those experienced only during periods of massive socioeconomic crisis in the 20th century, such as World War II and the collapse of communism ( Fig. 1).

Here, the historically decisive question is whether and how such rapid rates of deployment can be collectively achieved. Current deployment rates of low-carbon energy sources are compatible with the required shift but when scaled up are expected to encounter considerable resistance due to the rigidities inherent in political and economic decision making ( 7, 8), as well as new technological demands ( 9, 10). Although an increasing number of countries have already introduced or are committed to introducing carbon pricing, the initiatives covered by carbon pricing included only 15% of global greenhouse gas emissions in 2017 ( 11) and have so far driven only marginal emission reductions ( 12). It is increasingly recognized that business-as-usual technological progress and carbon pricing alone are not likely to lead to rapid and deep reductions in greenhouse gas emissions ( 13).

At the same time, there is evidence from various scientific fields demonstrating that rapid rates of change can be observed under certain critical conditions in natural ( 14⇓ - 16), socioeconomic ( 17⇓ ⇓ - 20) and social-ecological systems (SESs) ( 21, 22). Increasing attention is being given to the concept of tipping dynamics as a nonlinear mechanism behind such disruptive system changes. Based on a review on social-ecological tipping points research, Milkoreit et al. ( 23) propose a common definition of social tipping points (STPs) as points "within an SES at which a small quantitative change inevitably triggers a non-linear change in the social component of the SES, driven by self-reinforcing positive-feedback mechanisms, that inevitably and often irreversibly lead to a qualitatively different state of the social system." There are historical examples of dynamic social spreading effects leading to a large self-amplification of small interventions: For example, the writings of one man, Martin Luther, injected through newly available printing technology into a public ready for such change, triggered the worldwide establishment of Protestant churches ( 24). An example in the field of climate policy is the introduction of tariffs, subsidies, and mandates to incentivize the growth of renewable energy production. This has led to a substantial system response in the form of mutually reinforcing market growth and exponential technology cost improvement ( 25, 26).

In this paper, we examine a number of potential "social tipping elements" (STEs) for decarbonization ( 27, 28) that represent specific subdomains of the planetary social-economic system. Tipping of these subsystems could be triggered by "social tipping interventions" (STIs) that could contribute to rapid transition of the world system into a state of net zero anthropogenic greenhouse gas emissions. The results reported in this study are based on an online expert survey, an expert workshop, and an extensive literature review (SI Appendix).

Our results complement the existing shared socioeconomic pathways (SSPs) that are used alongside the representative concentration pathways (RCPs) to analyze the feedbacks between climate change and socioeconomic factors, such as world population growth, economic development, and technological progress ( 29). Our results could be useful for exploring possible transformative pathways leading to scenarios that reach net zero emissions by 2050 ( 30).

Defining STEs and STIs Relevant for Decarbonization Transformation

Various types of tipping processes can be differentiated in the literature. Many authors refer to critical thresholds ( 16, 28), a notion closely related to the metaphor of a "butterfly effect" ( 31, 32). Other processes related to tipping dynamics include metamorphosis, where a rapid loss of structures of one sort occurs simultaneously with the development of new structures ( 33), as well as cascades driven by positive feedbacks in processes occurring simultaneously at smaller scales ( 34).

The social tipping dynamics of interest for this study are typically manifested as spreading processes in complex social networks ( 35, 36) of behaviors, opinions, knowledge, technologies, and social norms ( 37, 38), including spreading processes of structural change and reorganization ( 34). These spreading processes resemble contagious dynamics observed in epidemiology that spread through social networks ( 39). Once triggered, such processes can be irreversible and difficult to stop. Similar contagious dynamics have been observed in human behavior ( 35, 36), for example in assaultive violence ( 39), participation in social movements ( 40), or health-related behaviors and traits ( 36), such as smoking or obesity ( 41, 42).

We understand STEs as functional subsystems of the planetary-scale World-Earth system ( 43) consisting of interacting biophysical subsystems of the Earth, and the social, cultural, economic, and technological subsystems of the world of human societies ( 43, 44). Potential STEs share one defining characteristic: A small change or intervention in the subsystem can lead to large changes at the macroscopic level ( 23) and drive the World-Earth system into a new basin of attraction, making the transition difficult to reverse ( 20). Exact quantifications of the relationship between big and small are, however, rare, as are empirical examples ( Table 1). For the combination of big interventions and big effects, there are currently no convincing examples; however, the potential use solar radiation management geoengineering in the future would fall into this category. Finally, some changes in the World-Earth system might be driven by nonhuman and unintentional forces (e.g., a sufficiently large meteorite hitting the Earth or a disease outbreak), while others might be driven by conscious interventions of human agency ( 45).

Tipping processes might be analyzed as a function of change in a suitably selected forcing variable or control parameter ( 15, 27). The pertinent World-Earth system features such as the anthropogenic carbon emissions are commonly the product of complex interactions of multiple drivers. These factor can, however, in some cases be combined into a single dominant control parameter.

In this study, we identify a subsystem of the World-Earth system as a STE relevant for decarbonization transformation if it fulfils the following criteria:

C1. A set of parameters or drivers controlling its state can be described by a combined control parameter that after crossing a critical threshold (the STP) by a small amount influences a crucial system feature of relevance (here the rate of anthropogenic greenhouse gas emissions) leading to a qualitative change in the system after a reference time has passed allowing for the emergence of the effect ( 15).

C2. It is possible to differentiate particular human interventions leading to the small change in the control parameter that has a big effect on the crucial system feature, which will be referred to as the STI ( Fig. 2).

Established social systems, including their infrastructures, while they may partly be open to change, tend also to possess self-stabilizing mechanisms that oppose change, be it through infrastructural inertia due to investment cycles or cultural or political inertia due to deeply held traditions or power structures all representing aspects of social complexities ( Fig. 2 and refs. 46 and 47). For this reason, a cumulation of effects due to social contagion, repetitive nudging, or direct intervention can lead to social tipping dynamics ( 48). Starting points for such cumulations of effects are here called STIs. Naturally, their existence, nature, and point of departure are a function of the cumulated history of the respective social system and, in that sense, STIs and social tipping dynamics are path dependent.

Following Rockström et al. ( 6), in order to achieve the Paris Climate Agreement's goals and to avoid higher levels of global warming at the end of this century that would imply crossing dangerous tipping points in the Earth's climate system ( 27), global anthropogenic carbon emissions would need to be halved every decade, achieving a peak in 2020 and then steadily decreasing to reach net zero emissions by 2050. Achieving net zero global emissions around 2050 is necessary for there to be a significant probability of limiting global warming to 1.5 °C by the end of the century ( 1). To ensure that the social tipping dynamics identified in this study are compatible with these constraints, we impose the following filtering criteria:

F1. The time needed to trigger the tipping should not exceed ∼15 y, and the time needed to observe a qualitative change at the whole system level should not exceed ∼30 y ( Fig. 1).

F2. Since abrupt social changes have historically often been associated with social unrest, war, or even collapse ( 49), human intervention and its foreseeable effects should here be explicitly compatible with the Sustainable Development Goals ( 50), in the sense of positive social tipping dynamics ( 34).

Finally, due to the networked and multilevel character of the social system ( 51), we also ask about the feedback mechanisms connecting and potentially mutually reinforcing the identified candidates for STEs and STIs.

Results

Candidates for STEs from Expert Elicitation.

Both natural and social systems are characterized by a high level of complexity and are linked by coevolutionary dynamics ( 52). Isolating the elements of such systems is difficult. Although we provided our respondents with a written definition of a STE, most of the online survey participants referred to what we define as STIs. On the basis of the responses, 12 groups of candidates for STEs could be identified, each referring to a distinctive control parameter ( Table 2). The critical threshold of the control parameter needed to be crossed in order to trigger the tipping process was in most of groups not quantified by the experts but described qualitatively. The STP was often referred to as the point when a certain belief, behavior, or technology, spreads from a minor tendency to a major practice. Documented instances of technology and business solutions show that a 17 to 20% market or population share can be sufficient to cross the tipping point and scale up to become the dominant pattern ( 53). Some authors, however, argue that it must be the "right" share of population, including well-connected influential people, trendsetters, and other types of social leaders with a high degree of agency ( 38, 54). In other cases, the experts referred to the STP that would be achieved if the price of fossil-fuel-free products and services falls below that of those products and services based on fossil fuels. Table 2 presents an overview of expert elicitation results.

Critical Interventions for Inducing Social Tipping Dynamics.

Building upon the results of our expert elicitation, we differentiated six key candidates for STEs and associated STIs for which we were able to find empirical material showing that they fulfill the conditions specified in our definition (as listed in Table 3). These do not necessarily comprise a comprehensive list of "silver bullet" solutions; rather, this is an initial selection that can help in developing more refined socioeconomic rapid transformation pathways and narratives customized at appropriate scales. Below, we present a review of literature on each of the STEs and STIs nominated by the experts. We search for evidence supporting the potential of the interventions to trigger tipping-like changes in their domains leading to a qualitative change at the World-Earth system level; we ask whether critical thresholds in the control parameters can be determined; and finally we begin to examine the interactions and feedbacks among the identified tipping elements.

STIs in the energy production system.

The technological development in the energy production system is a dominant element of the decarbonization discussions in international institutions ( 55, 56) and business partnerships ( 57). The results of our expert elicitation confirm that technology development is likely to play a key role, however, not in the sense of yet-to-be invented technological solutions, but rather in the adaptation of existing carbon-free technology primarily in the power sector and by facilitating a smarter utilization of energy. The main control parameter that drives the adaptation of fossil-fuel-free energy technology is associated with the financial returns of its adoption ( 58). Our expert group believed that the critical condition needed to trigger the tipping process is the moment when fossil-fuel-free energy production yields higher financial returns than the energy production based on fossil fuels. The empirical data show that this critical threshold is about to be reached; the prices of renewables have dropped sharply in the last few years, and they have already become the cheapest source of energy in many world regions. The average cost of onshore wind dropped by 18%, and offshore wind fell by 28% ( 59). The costs of photovoltaic modules fell by about 20% with every doubling of cumulative capacity since the 1970s ( 60) and the key role in reducing the cost of photovoltaics was played by policies that stimulate market growth ( 26). Optimization modeling shows that renewable energy supplies can potentially supply 100% of human power demand ( 61), and in theory, rapid transformation to low energy demand is possible ( 30) and will be cost-effective in the long run ( 62). However, there are large costs associated with adapting existing infrastructure and supply and demand support services to meet the demands of nondispatchable, volatile renewable sources like wind and solar in electricity generation. The question is whether the cost of transforming the energy infrastructure is worthwhile compared to the cost of inaction. The prioritization of societal preferences in the competition for scarce budgetary resources is influenced by the dominant social values ( 63).

Our expert group believed that redirecting national subsidy programs to renewables and low-carbon energy sources or removing the subsidies for fossil-fuel technologies are the tipping interventions that are needed for the take-off and diffusion of fossil-fuel-free energy systems. The key actors who have the agency to implement these interventions include national governments and energy ministries, and the response of large energy companies is important. One-third of global industrial greenhouse gas emissions can be linked just to 29 oil and gas companies ( 64). The International Energy Agency has tracked fossil-fuel subsidies over the last decade and in 2009 estimated that $312bn was spent worldwide in fossil-fuel subsidies, compared to $57bn on renewables in that year ( 65). By 2015, the gap had narrowed, but the subsidies received by fossil fuels were still more than twice those of renewables ( 66). Estimates show that a universal phaseout of fossil-fuel subsidies could lower annual carbon emissions by 4.4% ( 67). Coady et al. ( 68) argue that eliminating subsidies for fossil fuels would have reduced global carbon emissions in 2013 by 21%.

Furthermore, our expert group believed that the global energy production and storage system can also be radically changed by decentralization of energy production. Since large power stations relying on coal, oil, or gas exploitation are not profitable below a certain threshold of households supplied, decentralized generation systems and transitioning to local power generation might be expected to lead to a virtually complete decarbonization of production systems ( 69, 70). However, this is also likely to lead to an increase in costs due to the loss of economies of scale ( 69), and the complexities of integrating variable, distributed power sources ( 71). This emphasizes the need for decentralized energy generation and demand management to be part of the wider energy systems transformation ( 72). It has been argued that citizens also have a major role to play as nodes in a smart system capable of facilitating flexible demand management ( 73). Some authors also warn that meeting current levels of demand (let alone future projected demand) with renewables alone is likely to be extremely difficult ( 74, 75). Nonetheless, interest in decentralized control of energy systems is growing. Across the Global North, there are a multitude of examples of energy cooperatives and community-driven energy projects ( 76). Such projects have often found creative ways to overcome limitations imposed by centralized distribution networks, e.g., by using smart technologies to divert excess power for local heating ( 77), or by bringing municipal supply networks into community ownership ( 78). They show such initiatives may also spark around the Global South by skipping the "megadevelopment" phase associated with large power stations and massive grid infrastructure expansion. Due to the positive knowledge and technology spillover effects from such decentralized systems, the technology costs are likely to be further reduced with their increased diffusion ( 79, 80). The time elapsing between the planning phase and actual installation and utilization of decentralized energy generation is reportedly less than 10 y ( 81). However, existing energy systems and infrastructure are likely to shape the future for decades to come ( 82).

STIs in human settlements.

Direct and indirect emissions from buildings account for almost 20% of all carbon emissions, and we observe an unprecedented scale of global urbanization; each week the global urban population increases by 1.3 million ( 55). The average life span of buildings is about 50 y ( 83). Public infrastructure and planning structures can last even longer (50 to 150 y) and play an active role in both climate mitigation and adaptation ( 84). Modifying building codes for construction and infrastructural projects can actively drive the demand for fossil-fuel-free technologies and are crucial especially for countries in the Global South, where building booms are driving up energy and other resource use ( 85). An example of a STI in this realm is the creation of large-scale demonstration projects such as carbon-neutral cities. These are important in order to educate the general public and stimulate consumer interest in environmental technologies, accelerating their dissemination and commercialization ( 85). In addition, local technology clusters create positive spillover effects of lowering the information and transaction costs ( 86), which can indirectly lead to a reduction in the costs of fossil-fuel-free technologies for energy production and storage. The critical conditions for social tipping in this control parameter would be achieved if the fossil-fuel-free technology became the first choice for new construction and infrastructure projects. There are many new construction materials that not only imply lower emissions but also could actively support carbon sequestration efforts in urban areas. To give an example, constructing a 142-m-high residential building using above 80% laminated timber could lead to sequestrating 21,040 tons CO ₂ and avoiding 50,000 tons CO ₂ emissions otherwise entailed in using standard construction materials such as steel and concrete, which is equivalent to the amount 33,000 cars emit per year ( 87). In addition, large-scale public infrastructure investments support the emergence of a shared belief in the emerging new social equilibrium that can help individuals coordinate changes and find new focal points ( 88). The example of the Transition Town Movement that started in 2006 in the United Kingdom and in 2014 spanned over 41 countries shows how local grassroots initiatives can encourage citizens to take direct action toward lowering energy demand and building local resilience despite lack of policy support at national levels ( 89). Another example includes the Energy Cities Association, whose primary goal is to accelerate the transition to sustainable energy in urban areas in Europe. The Association was created in 1990 and currently represents more than 1,000 towns and cities in 30 countries ( 90). The evidence from a case study on communities implementing plans for zero emissions shows that these communities were able to reduce their per-capita emissions by 32% in 14 y ( 91).

STIs in the financial system.

The financial crisis in 2008 demonstrated how rapidly changes in the market value of assets in one sector and country can propagate and destabilize the global system of human societies and accelerate changes at the level of individual investment and consumption behavior as well as collective-organizational and policy responses ( 92). Maintaining global warming below 2 °C implies that 33% of oil, 49% of gas, and 82% of coal resources should not be burned ( 93). This suggests there might be a risk of a carbon bubble, caused by the financial exposure from stranded assets, which could be driven by policy, technological innovation, or investors' decisions ( 94). A growing number of analysts believe a financial bubble is emerging that could burst when investors' belief in carbon risk reaches a certain threshold ( 95). Simulations show that just 9% of investors could tip the system, inducing other investors to follow ( 96). An example of an intervention that can lead to a rapid decline in the control parameter-the value of fossil-fuel assets-is the divestment movement; as it progresses, it results in the reduction of the value of fossil-fuel assets ( 97). The movement started with a student campaign in 2011 and is quickly expanding to other countries and types of asset owners. The value of investment funds committed to selling off fossil-fuel assets reached $5.2tn in 2016, doubling in just over a year and permeating enterprises in every sector of society, with examples including universities, faith groups, pension funds, and insurance companies ( 98). Ritchie and Dowlatabadi ( 94) present model scenarios showing that a major Canadian university could reduce the greenhouse gas emissions tied to its investments by up to 26% by restructuring its portfolios, moving investments away from greenhouse gas-intensive sectors. Many divestment campaigns have an additional "divest to reinvest" element that advocates using funds invested in fossil-fuel companies to reinvest in socially and environmentally beneficial projects, such as low-carbon and renewable schemes ( 99), creating the positive-feedback interactions with the STE1. An avalanche effect would be triggered if national banks and insurance companies warned against the global risk associated to stranded assets from fossil-fuel projects. These concerns are growing in Europe, and there are already signs of a tipping point, namely cuts in financial and insurance support for coal projects ( 100). Norwegian financial authorities might soon be divesting the country's sovereign wealth fund. Around 6% (€30bn) of this fund's wealth is invested in oil and gas companies ( 101).

STIs in the system of norms and values.

The extraction and use of fossil fuels out of line with the Paris Climate Agreement targets is arguably immoral, as it would cause widespread grave and unnecessary harm ( 97). The impact of greenhouse gas emissions disproportionately affects the most vulnerable social groups, such as women and children ( 102). It also affects the well-being of future human generations ( 103) and causes many direct negative health effects ( 104). Historical cases show that social and moral norms can affect human behavior on a large scale ( 38). The abolition of the transatlantic slave trade, for example, showed that changes in the ethical perception of slave labor at that time were consciously initiated by a small group of intellectuals ( 105). Revealing the moral implication of the continued burning of fossil fuels is an example of an intervention that is likely to induce a tipping process through changes in the human normative system, i.e., the system of moral and behavioral norms that influence what is rewarded and desired in the society. Norms can develop through social networks in neighborhoods or workplaces and support certain lifestyles or technology choices ( 106). A study on the installation of photovoltaic panels by home owners showed social networks and dwelling proximity explained the owners' decision to install photovoltaic panels on their homes ( 107). The control parameter is represented by the ethical perception of fossil fuels, the environmental externalities they generate, and the broader harm they visit on societies. The critical condition in the control parameter will be achieved if the majority of social and public opinion leaders recognize the ethical implications of fossil fuels and generate pressure in their peer groups to ostracize the use of products involving fossil fuel burning. This could be more widespread in religious communities and be led by spiritual leaders, perhaps following the example of Pope Francis's encyclical Laudato si' ( 108). It could alternatively be manifested as a secular trend originating mainly from young, intellectually and social justice-oriented groups of people who might actively stand against supporters of fossil fuels-these would include extraction and utilization companies, governments supporting the latter, as well as the superrich family clans generating wealth from fossil fuel extraction and utilization in the last 150 y. The wealth of about 11% of the world's billionaires is related to energy production (excluding solar and wind), mining, and other natural resource utilization ( 109). Recent experimental evidence shows that dominant social conventions or established behavior can be changed by committed minorities of roughly 25% of a group ( 36). Social norms are the sources of law ( 110); therefore, recognizing the immoral character of fossil fuels can further lead to regulations restricting the use and extraction of fossil fuels ( 111).

The time elapsing from the recognition of the activity as a problem and as a matter of a moral choice by international legal scholars, religious groups, and other moral entrepreneurs, to international delegitimization might range from a few decades to a few centuries. The slavery abolition movement started in 1772 in England and led to the abolition of the slave trade in 1807 and in the 1833 to the total abolition of slavery in the British Empire. The historical data show that although the number of slaves traded in the British Empire dropped to zero by 1826, the number of internationally traded slaves started to decrease around the mid-19th century. However, after reaching its peak, the number of slaves traded internationally decreased exponentially within just a few years. In the period 1851 to 1860, 71% fewer slaves disembarked than in the period 1841 to 1850 ( https://slavevoyages.org/). A more recent example of outlawing the use of substances responsible for ozone depletion showed that such changes might occur in less than 30 y ( 112). However, the financial and political power of the fossil fuel industry suggests the need for much more substantial political effort to ensure such a change, than would have been the case for the issue of ozone depletion ( 99). There is recent anecdotal evidence that protests, such as the #FridaysForFuture climate strikes of school students around the world, the Extinction Rebellion protests in the United Kingdom, and initiatives such as the Green New Deal in the United States, might be indicators of this change in norms and values taking place right now ( 113).

STIs in the education system.

Many examples of research confirm the role of education in social transformations ( 114) and tackling climate change concerns ( 115, 116). The control parameter that relates to this intervention is the coverage of climate change issues in school and university teaching programs. While many teachers include some, often thin, coverage of climate change ( 117), comprehensive approaches at all levels of public education are still rare. Lack of knowledge about the causes, impacts, and solutions to climate change was the most easily identifiable individual barrier to engagement in climate action in the United Kingdom ( 118). At the same time, studies show that the divergent ways of understanding climate change draw on discourses broader than scientific knowledge; these differences may be blamed for misinterpretation of scientific notions such as uncertainty ( 119) as well as for the tendency to attribute responsibility for causing and mitigating climate change to others ( 118). Formal and lifelong education is traditionally considered a slow and evolving process, but there are examples of rapid change that can be generated. Quality education supports and amplifies norms and values and can quickly inspire behavior change among individuals and their cohorts. In addition, massive literacy campaigns, such as the one that took place in Cuba in the 1950s, where in a less than a year illiteracy was reduced from 24 to 3.9% ( 120), demonstrate the potential for rapid societal transformation. The effects of changes in educational programs can also lead to a social tipping process as soon as the new generation enters the job market and public decision-making bodies. The recent #FridaysForFuture protests demonstrate the upcoming new generation might radically change the political scene. It is estimated that within just half a year the school children movement grew to 1.5 million students in 125 countries. The effects of educational campaigns can be strengthened by a supportive family and community context as well as by media campaigns, advertising bans, higher taxes, use prohibitions, and lawsuits against producers ( 121). Warner ( 122) shows that combined educational and mass-media campaigns in the 1970s in the United States led to 4 to 5% annual decrease in cigarette consumption. In the climate change context, Dietz et al. ( 123) show that interventions that combine mass-media messages, household- and behavior-specific information, and communication through individuals' social networks and communities could lead to reductions of 20% in household direct emissions in less than 10 y, with little or no reduction in household well-being. An educational campaign carried out in five Italian cities for 2 y, involving teachers, pupils, and citizens, resulted in an emission reduction in a range of 7 to 30% in the 247 families included in the research ( 124). That said, education to bolster understanding of the causes and effects of climate change, however important, will not be sufficient to transform society alone. Sustainability cannot be imposed, it has to be learned, so that is endogenously realized and enacted deliberately by the actors who constitute the SES ( 46). Engagement and the fostering of sustainable lifestyles and career pathways by transforming schools into living laboratories ( 125) is necessary to counter the often overlooked shadow side of education, since the secondary and higher levels of education are currently associated with higher resource use ( 126).

STIs through information feedbacks.

The last tipping intervention is related to the flow of information and creating positive information feedbacks. The control parameter is represented by the transparency of the impact of individual consumer and lifestyle choices and carbon emissions. Transparency and disclosure of information about carbon emissions are needed, for instance, not just to provide a solid basis for global, regional, and national policies ( 127) but also to increase public and consumer awareness and improve labeling programs ( 128), triggering action and lifestyle changes to support decarbonization ( 129). The recent disclosure of the close ties between RWE, the biggest energy company in Germany, and regional politicians protecting their interest in the lignite coal extraction areas in Hessen led to a nationwide social movement and massive public demonstrations against plans to clear the Hambach Forest ( 130). Corporate disclosure of carbon assets can also help to overcome the short-term horizons of fund managers ( 131) and create a positive feedback in the divestment movement.

Another positive feedback can be identified between the information system and public education. Enhanced public knowledge and understanding by the broader public of the main variables and processes in the Earth's climate system and their linkages with human activities could increase public sensitivity to emissions-related information ( 132). Just as most product packages display nutritional facts, some authors propose they could display a second label on "Earth facts" and disclose the information on their carbon footprint and other emissions ( 133). In comparison, the global market for organic products, driven primarily by health concerns but clearly stimulated by providing clear labeling, increased at rates above 10% per year ( 134).

Discussion and Conclusions

Each of the STEs discussed above exists in the real world in varying degrees, locations, and scales and shows the potential to boost a decarbonization breakthrough. Since social-ecological dynamics are subject to complex processes that cannot be fully anticipated, it is not possible to predict when and where exactly tipping points will be crossed. However, the system can be imperfectly navigated intentionally to achieve certain desirable conditions and capacities ( 34). The social tipping dynamics are likely to spread through adaptive networks of interactions rather than via straightforward cause-effect systems. The identified interactions between the various STEs mean that they can potentially reinforce one another, making a transition to decarbonization more likely if several are triggered simultaneously ( Fig. 3). In addition, crossing multiple tipping points in diverse systems of action increases the likelihood of breaking existing systemic inertia and lock-ins and thereby achieving the climate policy goals ( 34, 45). The interactions between the nominated candidates for STEs could be organized as different possible transformative pathways leading to crossing tipping points across scales and regions. These "tipping transformative pathways" can potentially show the bottom-up emergence of the global sustainability pathway (SSP1) ( 135).

One possible transformative pathway that has recently started to materialize has been initiated within the education system by school children who started the climate strikes #FridaysForFuture. The movement is causing "irritations" in personal worldviews ( 136) and thus might be changing peoples' norms and values and the ways of thinking and acting, possibly leading to changes in policies and regulations, infrastructure development, as well as individual consumption and lifestyle decisions. For example, as a result of the massive school student protest in Germany, even the traditionally climate-conservative parties recently started to address climate change issues in their programs ( 137). The increasing awareness of the seriousness of climate change might drive an increasing demand for greenhouse-gas emission disclosure of various products and services. It might also drive an increased recognition of the intergenerationally unethical and immoral character of fossil fuels that will furthermore strengthen the legitimacy of carbon mitigation policies, including the removal of fossil-fuel subsidies. Although changes of norms, customs, and beliefs occur very slowly ( 138), one should keep mind that now is not year zero of the global sustainability transformation. It has now been 30 y since the Intergovernmental Panel on Climate Change (IPCC) was endorsed by the United Nations and issued its first report recognizing the anthropogenic character of climate change, and many important milestones have been reached since then, including publishing the subsequent IPCC reports, Pope Francis's encyclical Laudato si', and numerous events led by artists and activists increasing the concern about climate issues. The example of "flight shaming" that was initiated by a Swedish Olympic athlete and has been popularized in social media ( 139), shows that society may now be just at the edge of tipping in the realm of social norms and beliefs. The high number of seats that environmentally oriented parities recently won in the European Union (EU) elections ( 140) shows that EU policy might potentially undergo a substantial shift within the next few years, the EU becoming a global leader in carbon mitigation efforts.

A global breakthrough could also be initiated at the level of resource allocation by redirecting financial flows in line with the divestment movement and improving information feedbacks by disclosing the greenhouse gas emissions of products and services. At this level, firms take consumption and production decisions constrained by budget as well as by information and technology availability ( 20, 51). Changes at this level occur continuously. Very rapid changes, at a rate of 50% or more, can occur within a few months. This is shown by public opinion polls on, for example, political preferences following information flows, particularly in online social media ( 141). Rapid changes in stock markets can occur within hours ( 142). Nevertheless, such trends rarely lead to bigger changes in human societies without simultaneous institutional changes. The institutional changes, requiring more time, such as transforming the public subsidies and taxation systems, are needed to stabilize the new emerging system. Otherwise the system might become increasingly unstable, bouncing back and forth between the old and new social order, delaying the transformation. A well-documented example of such a phenomenon is the rebound effect ( 143, 144). Even the frequently quoted "successful" example of feed-in tariffs and German energy transition "Energiewende" to renewables, which used the rapid change in public opinion in the aftermath of the nuclear catastrophe in Fukushima in Japan in 2011, have recently faded away due to the lack of sufficiently sustained societal and policy support ( 145).

Many of the nominated candidates for STEs extend beyond achieving greenhouse gas reduction and can be potentially interlinked with achieving other global policy goals, such as the Sustainable Development Goals. Many of the interventions discussed above include a range of well-being and public health cobenefits ( 68). Solving the climate crisis could be a chance to redesign the global socioeconomic institutions toward achieving a more just and equitable future ( 146). Several authors point out that environmental catastrophes, including increased severity and frequency of climatic extremes, might act as "windows of opportunity" that give rise to uncertainty and confusion, which might in turn motivate actors to engage in reflective processes and take sharp breaks from the existing procedures and policies ( 147) ( Fig. 3). However, although the opportunity for a revolutionary change might emerge due to external or environmental factors ( 148), it is important to actively work with the social complexities ( Fig. 2) and the relevant key social actors ( Tables 2 and 3), to increase public acceptance and support for the transformative changes to come. To ensure that climate-related social learning will take place, it is necessary to understand how changes of perceptions and awareness, motives, and interests of various actors take place and how institutional innovations occur ( 149).

We call on both social and natural sciences to engage more intensively in collaborative interdisciplinary research to understand rapid social transformations, STEs, and their interactions with tipping elements in the Earth system. Planetary social-ecological models and machine-learning techniques can help to explore the control parameters and critical thresholds in the trajectory of this World-Earth coevolutionary dynamics ( 43). We also encourage studies on the archetypes of social transformations ( 150) in different world regions as well as using insights and methods from the natural sciences to study the complexity of social systems. Both empirical studies and modeling exercises could also help to assess the distributional impacts of STIs and factors influencing their effectiveness. Our study presents a comprehensive empirical analysis of social tipping dynamics for global decarbonization. However, since our results were derived from an elicitation process involving small and nonrepresentative samples of experts, more research is needed to verify our findings and to provide more robust empirical evidence and data. Experts from the research sector and the Global North were overrepresented in our sample. Therefore special attention should be given to the expertise of low-carbon and sustainability practitioners as well as to providing more empirical material from the Global South. Finally, the urgency and complex character of climate change require transdisciplinarity and engagement with social movements, knowledge brokers, and change leaders ( 151). More research is needed on understanding the required social processes and the drivers and incentives for short-term engagement of diverse coalitions of action around concrete solutions and strategies at various governance levels ( 152).

Materials and Methods

The primary data collection tool was an online expert survey that was sent to over 1,000 international experts through a private message or addressed through mailing lists of organizations in the field of climate change and sustainability. A full list of all survey questions as well details on the research organization are provided in SI Appendix. The survey ran for 2.5 mo, and it was completed by 133 experts. In total, they suggested 207 candidates for STEs and interventions instrumental for decarbonization by 2050. A selected group of 17 experts were invited for a workshop that focused on choosing the top candidates for STEs. Finally, the coauthors carried out a literature review on the top candidates selected at the workshop, following the literature review guidelines.

Data Availability Statement.

All data discussed in the paper will be made available to readers upon request.

Acknowledgments

We acknowledge financial support by the Earth League's EarthDoc program, the Stordalen Foundation ( http://pb.net/ Network), the Leibniz Association (DominoES), and the European Research Council (Earth Resilience in the Anthropocene). We thank James Greyson, Claudia Köhler, Sangjun Park, Anja Klein, Andrzej Ancygier, Frank Wechsung, Doyne Farmer, Tim Lenton, Jobst Heitzig, Ricarda Winkelmann, Alison Schlums, Maria Martin, Konrad Hagedorn, the WINS Group, and the research participants.

Footnotes

Author contributions: I.M.O., J.F.D., R.C., A.B., W.L., J.R., and H.J.S. designed research; I.M.O., J.F.D., R.C., A.B., R.J.H., F.A., M.M., S.S.P.D., A.L., N.M., and D.P.v.V. performed research; I.M.O., J.F.D., W.L., and J.R. contributed new reagents/analytic tools; I.M.O., J.F.D., R.C., A.B., and F.A. analyzed data; and I.M.O., J.F.D., R.C., A.B., R.J.H., W.L., J.R., F.A., M.M., S.S.P.D., A.L., N.M., D.P.v.V., and H.J.S. wrote the paper.

Reviewers: J.D.T., Autonomous University of Barcelona; and J.E.T., Massachusetts Institute of Technology.

The authors declare no competing interest.

This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1900577117/-/DCSupplemental.

View Abstract

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Social tipping dynamics for stabilizing Earth's climate by 2050

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Achieving a rapid global decarbonization to stabilize the climate critically depends on activating contagious and fast-spreading processes of social and technological change within the next few years. Drawing on expert elicitation, an expert workshop, and a review of literature, which provides a comprehensive analysis on this topic, we propose concrete interventions to induce positive social tipping dynamics and a rapid global transformation to carbon-neutral societies.

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On 11 October 2016, the Facebook page "Sustainable Business Network NZ" posted a photograph of a clipping from the 14 August 1912 edition of the Rodney and Otamatea Times, Waitemata and Kaipara Gazette that included a brief item headlined "Coal Consumption Affecting Climate":

The furnaces of the world are now burning about 2,000,000,000 tons of coal a year. When this is burned, uniting with oxygen, it adds about 7,000,000,000 tons of carbon dioxide to the atmosphere yearly. This tends to make the air a more effective blanket for the earth and to raise its temperature. The effect may be considerable in a few centuries.

This article's authenticity is supported by the fact it can be found in the digital archives of the National Library of New Zealand.

Further attesting to its authenticity (and perhaps its role as a bit of stock news used to fill space) is that an identical story had appeared in an Australian newspaper a month prior, in the 17 July 1912, issue of The Braidwood Dispatch and Mining Journal, as found in the digital archives of the National Library of Australia.

An even deeper dive reveals that the text of this news item has its origins in the March 1912 issue of Popular Mechanics, where it appeared as a caption in an article titled "Remarkable Weather of 1911: The Effect of the Combustion of Coal on the Climate - What Scientists Predict for the Future":

Some online commenters expressed skepticism over the notion that such a clear understanding of the mechanisms relating to greenhouse gases existed in 1912, or that anyone back then would have suggested humans could play a role in altering their concentration. In fact, the timing of these news clips is consistent with the historical record.

The first person to use the term "greenhouse gases" was a Swedish scientist named Svante Arrhenius in 1896. In a paper published that year, he made an early calculation of how much warmer the Earth was thanks to the energy-trapping nature of some of the gases in the atmosphere. Even at this early stage, he understood that humans had the potential to play a significant role in changing the concentration of at least one of those gases, carbon dioxide (carbonic acid back then):

The world's present production of coal reaches in round numbers 500 millions of tons per annum, or 1 ton per km of earth's surface. Transformed into carbonic acid, this quantity would correspond to about a thousandth part of the carbonic acid in the atmosphere.

Though he didn't explicitly say in that paper that human activity could warm the planet, Arrhenius would go on to make that argument in later works. A 2008 tribute to Arrhenius published by the Royal Swedish Academy of Engineering Sciences stated that his ideas about coal and climate were popular and well known in his day but fell out of favor for a while after his death in 1927:

While Arrhenius' prediction [of warming] received great public interest, this typically waned in time but was revived as an important global mechanism by the great atmospheric physicist Carl Gustaf Rossby who initiated atmospheric CO ₂ measurements in Sweden in the 1950s.

In this sense, the content and date of the newspaper clips in question are consistent with both what was known to scientists about greenhouse gases then and what the general public was interested in at the time.

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Did a 1912 Newspaper Article Predict Global Warming?

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On 11 October 2016, the Facebook page "Sustainable Business Network NZ" posted a photograph of a clipping from the 14 August 1912 edition of the Rodney and Otamatea Times, Waitemata and Kaipara Gazette that included a brief item headlined "Coal Consumption Affecting Climate": The furnaces of the world are now burning about 2,000,000,000 tons of coal a year.

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Not Cool Ep 3: Tim Lenton on climate tipping points by Future of Life Institute

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What is a climate tipping point, and how do we know when we’re getting close to one? On Episode 3 of Not Cool, Ariel talks to Dr. Tim Lenton, Professor and Chair in Earth System Science and Climate Change at the University of Exeter and Director of the Global Systems Institute. Tim explains the shifting system dynamics that underlie phenomena like glacial retreat and the disruption of monsoons, as well as their consequences. He also discusses how to deal with low certainty/high stakes risks, what types of policies we most need to be implementing, and how humanity’s unique self-awareness impacts our relationship with the Earth.

Topics discussed include:

    Climate tipping points: impacts, warning signals
    Evidence that climate is nearing tipping point?
    IPCC warming targets
    Risk management under uncertainty
    Climate policies
    Human tipping points: social, economic, technological
    The Gaia Hypothesis

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You will not be surprised to learn that the climate crisis is a big and complicated problem. But when I started Not Cool, a Climate Podcast, I honestly hoped that if I could just talk with a few climate experts, we could clarify the facts and outline straightforward solutions. Thirty-one experts and 26 interviews later, I realize how mistaken I was, with more questions now than when I started. But I've also learned some amazing facts about how nature works, how humans work, and how to start addressing this crisis.

1) Zoning laws save lives

Zoning laws might seem inconsequential, but they can also save lives. The deadly fire in Paradise, California, and the flooding from Hurricane Harvey were as much about lax zoning laws as they were about extreme events caused by climate breakdown. Regardless of how quickly we bring down our emissions, we have some warming already locked in, which means there will be more fires, hurricanes and rising sea levels. Zoning laws help people stay safe in more extreme and frequent disasters.

2) Cement is killing the planet

Integral to our zoning laws are the building materials we use. Cement, for example, accounts for approximately 8-10% of all global carbon emissions. Roughly half of those emissions come from the carbon removed during the process of making cement, while the other half result from the energy required to make cement. Steel poses similar problems. Ironically, these carbon-emitting materials are often used in climate change adaptation solutions like sea walls.
The climate science is clear: it's now or never to avert catastrophe | Bill McKibben
3) We need more mangroves

Fortunately, nature provides incredible tools for addressing and adapting to climate change. Mangroves - essentially forests that grow along coastlines - are near magical solutions that came up in multiple interviews. They help prevent erosion and protect coastal regions from waves and rising sea levels. The trees are a haven for biodiversity, which could be partly why coral reefs seem to thrive in their presence. And mangroves also sequester a lot of carbon, which can help address both global heating and ocean acidification - an effect of the increased carbon in the oceans.

4) Healthy oceans absorb carbon

Our oceans take in a shocking amount of carbon - about 25% to 30% of all emissions. We can thank our oceans for ensuring that climate breakdown isn't worse, but that also means that ocean acidification is a huge problem, especially in polar regions where the colder water absorbs more gas. Though some people hope technical solutions like geoengineering could help address global heating, these won't help ocean acidification.

5) Forget geoengineering - we have forests

There are two types of geoengineering, more accurately known as climate engineering. One highly contentious method involves injecting particulates, such as sulfur aerosols, into the sky to minimize solar radiation and decrease temperatures. The problem with this approach is that if countries disagree about optimal global temperatures, we can't just suddenly stop the geoengineering systems, as this would cause global temperatures to rise quickly and dramatically. But if left unaddressed, serious international disagreement could lead to war. The other - far less contentious - geoengineering option involves pulling carbon out of the atmosphere. Though technologies for this exist, they're not yet affordable or scaleable. But nature could again help here, as more forests could absorb more carbon, cooling the Earth.

6) The trees in the Amazon are the world's ... sweat glands?

The Amazon rainforest is not the world's lungs; it's our sweat glands. Most of the oxygen we breathe actually comes from marine organisms like phytoplankton (another reason to be grateful for oceans). Instead, forests are useful because they pull moisture from the soil and expel it through their leaves, cooling the Earth just as sweat cools our bodies. So not only are forests vitally important for reabsorbing the carbon we emit, they also decrease temperatures. Unfortunately, many forests - especially the Amazon - face deforestation. Some researchers fear that if even 25% to 30% of the Amazon rainforest is cut down, the loss of moisture could change its basic makeup, transforming it from a rainforest to a savanna. This threat remains speculative, but is it possible we've already passed other critical tipping points?

7) Humans might be reaching a climate tipping point ... and that's a good thing

Climate systems like to be in equilibrium. If we push them out of equilibrium, past their tipping points, we could trigger feedback loops and exacerbate global warming. For the most part, these are considered future threats, so it was disconcerting to learn that we may have already tipped the West Antarctic Ice Sheet into a state of irreversible melting. If that's the case, we can expect ocean levels to rise even more than predicted with current warming levels. On the other hand, many of the experts I spoke with also hope we may be on the verge of a human tipping point. As many pointed out, past cultural shifts happened slowly, then suddenly. If climate crisis awareness and concern increase at their current pace, we may yet be able to make the changes necessary to ward off the worst climate threats.

8) The scientific consensus around climate change matters

Perhaps one sign that we're nearing a human tipping point is the incredible scientific consensus surrounding climate change. I didn't formerly care that 97% of climate scientists agree about climate change. I cared about the actual scientific studies that clearly show the Earth is warming. But consensus is more relevant than I realized. First, this level of scientific consensus doesn't occur unless the science is really robust. Second, most people don't have time to read all of the science. They have to put their trust in experts, and when 97% of experts say something is true, the public typically listens. The problem is that many people don't realize how strong climate consensus is.

Perhaps the most important thing to know about the climate crisis is that solutions exist. It's political will we lack

9) Talking about climate change is powerful

Talking about the climate crisis can have a powerful impact. Just talking more can help address confusion about climate facts and help us all realize that public consensus regarding climate change is quite broad. This doesn't mean quoting climate science to your conservative uncle at a holiday dinner. You could have a conversation about the money you saved by getting an electric car or bike, or that you want solar panels because they make you more self-sufficient and will save you money in the long run.

10) Switching your bank could be the most green thing you ever do

Looking for another easy way to address the climate emergency? Talk to your bank. Many banks help fund the fossil fuel industry, and if yours is doing so, you can switch to a bank or credit union that doesn't. As an individual, you can and should vote - but while we wait for better climate policies, moving your money could be one of the most impactful actions you can take to de-fund the fossil fuel industry. Fun statistic: people are more likely to leave their spouse than their banks.

Perhaps the most important thing to know about the climate crisis is that solutions exist. It is political will we lack. Many people worry about convincing climate deniers that climate breakdown is real, but deniers make up a very small percentage of the population. Our real focus should be on convincing those in power that the majority of us want to see strong political action. That happens when we talk to each other, when we talk to our representatives, and when we talk to our financial institutions. Individual climate action is critical, but this is ultimately a societal problem, and the solution must be societal as well.

Ariel Conn is the host of Not Cool, a Climate Podcast, the former director of communications and outreach for the Future of Life Institute, and the founder of Mag10 Media, an organization dedicated to improving science communication

Topics

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Trees in the Amazon are the world's sweat glands - and 10 other essential climate facts | Ariel Conn

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You will not be surprised to learn that the climate crisis is a big and complicated problem. But when I started Not Cool, a Climate Podcast, I honestly hoped that if I could just talk with a few climate experts, we could clarify the facts and outline straightforward solutions.

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The tipping points at the heart of the climate crisis | Science | The Guardian

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The tipping points at the heart of the climate crisis | Science | The Guardian

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he warning signs are flashing red. The California wildfires were surely made worse by the impacts of global heating. A study published in July warned that the Arctic is undergoing " an abrupt climate change event" that will probably lead to dramatic changes. As if to underline the point, on 14 September it was reported that a huge ice shelf in northeast Greenland had torn itself apart, worn away by warm waters lapping in from beneath.

That same day, a study of satellite data revealed growing cracks and crevasses in the ice shelves protecting two of Antarctica's largest glaciers - indicating that those shelves could also break apart, leaving the glaciers exposed and liable to melt, contributing to sea-level rise. The ice losses are already following our worst-case scenarios.

These developments show that the harmful impacts of global heating are mounting, and should be a prompt to urgent action to cut greenhouse gas emissions. But the case for emissions cuts is actually even stronger. That is because scientists are increasingly concerned that the global climate might lurch from its current state into something wholly new - which humans have no experience dealing with. Many parts of the Earth system are unstable. Once one falls, it could trigger a cascade like falling dominoes.

Tipping points

We have known for years that many parts of the climate have so-called tipping points. That means a gentle push, like a slow and steady warming, can cause them to change in a big way that is wholly disproportionate to the trigger. If we hit one of these tipping points, we may not have any practical way to stop the unfolding consequences.

The Greenland ice sheet is one example of a tipping point. It contains enough ice to raise global sea levels by seven metres, if it were all to melt. And it is prone to runaway melting.

This is because the top surface of the ice sheet is gradually getting lower as more of the ice melts, says Ricarda Winkelmann of the Potsdam Institute for Climate Impact Research in Germany. The result is familiar to anyone who has walked in mountains. "If we climb down the mountain, the temperature around us warms up," she says. As the ice sheet gets lower, the temperatures at the surface get higher, leading to even more melting. "That's one of these self-reinforcing or accelerating feedbacks."

We don't know exactly how much warming would cause Greenland to pass its tipping point and begin melting unstoppably. One study estimated that it would take just 1.6C of warming - and we have already warmed the planet 1.1C since the late 19th century.

The collapse would take centuries, which is some comfort, but such collapses are difficult to turn off. Perhaps we could swiftly cool the planet to below the 1.6C threshold, but that would not suffice, as Greenland would be melting uncontrollably. Instead, says Winkelmann, we would have to cool things down much more - it's not clear by how much. Tipping points that behave like this are sometimes described as "irreversible", which is confusing; in reality they can be reversed, but it takes a much bigger push than the one that set them off in the first place.

Satellite images of the disintegration of the Spalte glacier in northeast Greenland between 2013 and 2020. Photograph: EU Copernicus and Geus/Reuters

In 2008, researchers led by Timothy Lenton, now at the University of Exeter, catalogued the climate's main " tipping elements". As well as the Greenland ice sheet, the Antarctic ice sheet is also prone to unstoppable collapse - as is the Amazon rainforest, which could die back and be replaced with grasslands.

A particularly important tipping element is the vast ocean current known as the Atlantic meridional overturning circulation (AMOC), which carries warm equatorial water north to the Arctic, and cool Arctic water south to the equator. The AMOC has collapsed in the past and many scientists fear it is close to collapsing again - an event that was depicted (in ridiculously exaggerated and accelerated form) in the 2004 film The Day After Tomorrow. If the AMOC collapses, it will transform weather patterns around the globe - leading to cooler climates in Europe, or at least less warming, and changing where and when monsoon rains fall in the tropics. For the UK, this could mean the end of most arable farming, according to a paper Lenton and others published in January.

Tumbling dominoes

In 2009, a second study took the idea further. What if the tipping elements are interconnected? That would mean that setting off one might set off another - or even unleash a cascade of dramatic changes, spreading around the globe and reshaping the world we live in.

For instance, the melting of the Greenland ice sheet is releasing huge volumes of cold, fresh water into the north Atlantic. This weakens the AMOC - so it is distinctly possible that if Greenland passes its tipping point, the resulting melt will push the AMOC past its own threshold.

"It's the same exact principles that we know happen at smaller scales," says Katharine Suding of the University of Colorado, Boulder, who has studied similar shifts in ecosystems. The key point is that processes exist that can amplify a small initial change. This can be true on the scale of a single meadow or the whole planet.

However, the tipping point cascade is very difficult to simulate. In many cases the feedbacks go both ways - and sometimes one tipping point can make it less likely that another will be triggered, not more. For example, the AMOC brings warm water from equator up into the north Atlantic, contributing to the melting of Greenland. So if the AMOC were to collapse, that northward flow of warm water would cease - and Greenland's ice would be less likely to start collapsing. Depending whether Greenland or the AMOC hit its tipping point first, the resulting cascade would be very different.

What's more, dozens of such linkages are now known, and some of them span huge distances. "Melting the ice sheet on one pole raises sea level," says Lenton, and the rise is greatest at the opposite pole. "Say you're melting Greenland and you raise the sea level under the ice shelves of Antarctica," he says. That would send ever more warm water lapping around Antarctica. "You're going to weaken those ice shelves."

"Even if the distance is quite far, a larger domino might still be able to cause the next one to tip over," says Winkelmann.

In 2018, Juan Rocha of the Stockholm Resilience Centre in Sweden and his colleagues mapped out all the known links between tipping points. However, Rocha says the strengths of the interconnections are still largely unknown. This, combined with the sheer number of them, and the interactions between the climate and the biosphere, means predicting the Earth's overall response to our greenhouse gas emissions is very tricky.

Into the hothouse

The most worrying possibility is that setting off one tipping point could unleash several of the others, pushing Earth's climate into a new state that it has not experienced for millions of years.

Since before humans existed, Earth has had an "icehouse" climate, meaning there is permanent ice at both poles. But millions of years ago, the climate was in a "hothouse" state: there was no permanent polar ice, and the planet was many degrees warmer.

'Hothouse' conditions will make fires such as this one in the San Gabriel mountains above Azusa, California, in August more frequent. Photograph: Apu Gomes/AFP/Getty Images

If it has happened before, could it happen again? In 2018, researchers including Lenton and Winkelmann explored the question in a much-discussed study. "The Earth System may be approaching a planetary threshold that could lock in a continuing rapid pathway toward much hotter conditions - Hothouse Earth," they wrote. The danger threshold might be only decades away at current rates of warming.

Lenton says the jury is still out on whether this global threshold exists, let alone how close it is, but that it is not something that should be dismissed out of hand.

"For me, the strongest evidence base at the moment is for the idea that we could be committing to a 'wethouse', rather than a hothouse," says Lenton. "We could see a cascade of ice sheet collapses." This would lead to "a world that has no substantive ice in the northern hemisphere and a lot less over Antarctica, and the sea level is 10 to 20 metres higher". Such a rise would be enough to swamp many coastal megacities, unless they were protected. The destruction of both the polar ice sheets would be mediated by the weakening or collapse of the AMOC, which would also weaken the Indian monsoon and disrupt the west African one.

Winkelmann's team studied a similar scenario in a study published online in April, which has not yet been peer-reviewed. They simulated the interactions between the Greenland and west Antarctic ice sheets, the AMOC, the Amazon rainforest and another major weather system called the El Niño southern oscillation. They found that the two ice sheets were the most likely to trigger cascades, and the AMOC then transmitted their effects around the globe.

What to do?

Everyone who studies tipping point cascades agrees on two key points. The first is that it is crucial not to become disheartened by the magnitude of the risks; it is still possible to avoid knocking over the dominoes. Second, we should not wait for precise knowledge of exactly where the tipping points lie - which has proved difficult to determine, and might not come until it's too late.

Rocha compares it to smoking. "Smoking causes cancer," he says, "but it's very difficult for a doctor to nail down how many cigarettes you need to smoke to get cancer." Some people are more susceptible than others, based on a range of factors from genetics to the level of air pollution where they live. But this does not mean it is a good idea to play chicken with your lungs by continuing to smoke. "Don't smoke long-term, because you might be committing to something you don't want to," says Rocha. The same logic applies to the climate dominoes. "If it happens, it's going to be really costly and hard to recover, therefore we should not disturb those thresholds."

"I think a precautionary principle probably is the best step forward for us, especially when we're dealing with a system that we know has a lot of feedbacks and interconnections," agrees Suding.

"These are huge risks we're playing with, in their potential impacts," says Lenton. "This is yet another compulsion to get ourselves weaned off fossil fuels as fast as possible and on to clean energy, and sort out some other sources of greenhouse gases like diets and land use," says Lenton. He emphasises that the tipping points for the two great ice sheets may well lie between 1C and 2C of warming.

"We actually do need the Paris climate accord," says Winkelmann. The 2016 agreement committed most countries to limit warming to 1.5 to 2C, although the US president, Donald Trump, has since chosen to pull the US out of it. Winkelmann argues that 1.5C is the right target, because it takes into account the existence of the tipping points and gives the best chance of avoiding them. "For some of these tipping elements," she says, "we're already in that danger zone."

Cutting greenhouse gas emissions is not a surprising or original solution. But it is our best chance to stop the warning signs flashing red.

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The tipping points at the heart of the climate crisis

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he warning signs are flashing red. The California wildfires were surely made worse by the impacts of global heating. A study published in July warned that the Arctic is undergoing " an abrupt climate change event" that will probably lead to dramatic changes.

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The towering glaciers of West Antarctica hold the fate of the world's coasts in their flanks. Their collapse could send sea levels up by at least a foot by 2100-and potentially much more.

For years, scientists have watched and learned that those glaciers are crumbling and melting, the rate speeding up over the decades and imperiling the stability of the entire ice sheet. But while the science was clear that human influences on climate would affect the ice down the line, it has been hard to tell whether human-driven global warming has affected the melting already underway.

Now, a team has unraveled evidence of that human influence. In a study published Monday in Nature Geoscience, a team of scientists showed that over the past century, human-driven global warming has changed the character of the winds that blow over the ocean near some of the most fragile glaciers in West Antarctica. Sometimes, those winds have weakened or reversed, which in turn causes changes in the ocean water that laps up against the ice in a way that caused the glaciers to melt.

"We now have evidence to support that human activities have influenced the sea level rise we've seen from West Antarctica," says lead author Paul Holland, a polar scientist at the British Antarctic Survey.

The massive West Antarctic ice sheet holds something like 6 percent of the world's fresh water frozen in its guts. If it all melted away, global sea levels would rise by about 10 feet or more. That's not likely to happen anytime particularly soon, scientists think, but some parts of the ice sheet are particularly vulnerable, in danger of crossing a crucial "tipping point" if they retreat too far. ( Read about the "tipping point" here).

In the past decades, some glaciers in the region have been retreating shockingly quickly. Pine Island Glacier and Thwaites Glaciers, for example, are losing about 100 billion tons of ice each year, and more in bad years. ( See what a 10 billion ton chunk of ice looks like in this video).

The glaciers have been receding because their snouts spill over the edge of the continent into the surrounding ocean, which is warmer than the ice. The warm water melts away the ice.

Just how warm the ocean is, though, matters a lot. Over decades, the temperature of the water has waxed and waned, driven in part by natural climate cycles that send different water masses close to the edge of the ice sheet at different times, cycling through from cold to a little less cold every five years or so.

The main thing that controls whether warm water makes it to the edge of the ice sheet, it turns out, is the strength of the winds a little bit farther offshore, in the heart of the icy, bitter Amundsen Sea. Sometimes, those winds-cousins of the famous raging band of Southern Ocean winds known as the Roaring 40s-slacken or even reverse. When they do, more warm water ends up near the edge of the ice sheet, which means more ice melts away. ( See what the world would look like if all the ice melted away).

"In the 1920s, the winds were pretty much consistently blowing toward the west," says Holland. "So in the old days, it was cold all the time-it flopped between cold and very cold."

But now, because of the slow warming of the planet, the whole baseline has moved up. Instead of the cycle flipping between cold and very cold, the flip is between warm and cold.

Scientists knew that the strength of the winds in this region of the Amundsen Sea affected the water temperature. Records of wind strength and direction only went back until 1979. But the patterns in this region match up nearly perfectly with conditions far away, in the tropical Pacific Ocean, where much better, longer-term records exist-so the team could extrapolate how the polar-region winds have changed over the last century.

They used a suite of climate models to look at how the wind patterns would have evolved over the last 100 years if human-caused global warming weren't in play, and compared that with what the winds actually did. Today's pattern-with about equal west-flowing and east-flowing winds-means the whole region ends up quite a bit warmer than it was 100 years ago, when the wind flowed toward the west most of the time.

In the past, and even up to the early part of the record the scientists looked at in the 1920s, ice melted during warm phases and grew back during cold phases. But over the last century, that balance has come undone. The shifting winds and warm ocean phases have eaten away at the ice more quickly than it's being replaced.

Several particularly notable moments of wind-flipping, like in the 1970s, matched up closely with major retreats of the Pine Island and Thwaites glaciers.

Those glaciers are particularly sensitive to melting at their snouts. The ground underneath them, it turns out, is concave, like a bowl. The glacier ice is attached the "rim" of the bowl, but if it melts back past that edge, warm ocean water can spill underneath it and melt it even more quickly from the bottom.

In 1974, one of these strong moments of melting pushed the glaciers past one of these "rims," and since then the glacier has melted much more quickly than it did before-at least 50 percent more melt after that un-groundig than before, said Eric Steig, an atmospheic and ice core scientist at the University of Washington and an author of the paper.

The suspect has been identified-and it's us

The ultimate cause of the wind patterns, they found, is human-caused climate change. The extra greenhouse gases humans have pumped into the atmosphere over the past few hundred years have changed the way heat moves around the planet so thoroughly that they've changed the shape of the basic wind patterns at the poles.

The Antarctic ice sheet sat more or less stable in shape and size for many thousands of years. But about a century ago, pieces of it started to retreat in measurable ways. That's well within the time frame when carbon dioxide and other greenhouse gases had started to accumulate thickly in the atmosphere, so it seemed logical to think that human influence was affecting the ice. But Antarctica is a complicated place that changes a lot because of natural variability, so it has been challenging to pinpoint the extent of human influence on the changes.

"It was very hard to imagine that the ice sat around happily for millennia and then decided to retreat naturally just as humans started perturbing the system, but the evidence for forcing by natural variability was strong," writes Richard Alley, a climate scientist at Pennsylvania State University, in an email.

But a warming planet has very clearly changed the way winds move around Antarctica-and that change is likely to continue, unless something drastic happens to slow or reverse the warming process.

"If we carry this pattern forward, we may move to a situation where we're flipping between warm and very warm," says Holland. And that could be devastating for the ice.

But the future isn't yet written, Steig stressed. Keeping future greenhouse gas emissions in check would go a long way toward keeping those crucial winds from weakening further, the water under the edge of the ice chilly, and the ice frozen.

"[West Antarctic Ice Sheet] melting will affect everyone," says Steig. "The effects will be global, because sea level will rise globally."

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West Antarctica is melting-and it's our fault

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The towering glaciers of West Antarctica hold the fate of the world's coasts in their flanks. Their collapse could send sea levels up by at least a foot by 2100-and potentially much more. For years, scientists have watched and learned that those glaciers are crumbling and melting, the rate speeding up over the decades and imperiling the stability of the entire ice sheet.

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Eliza Mackintosh, CNNVideo by Edward Kiernan, CNN

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Finland is winning the war on fake news. Other nations want the blueprint

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Russia’s neighbor has developed a plan for countering misinformation. Can it be exported to the rest of the world?

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Melting Antarctic ice will raise sea level by 2.5 metres – even if Paris climate goals are met, study finds | Environment | The Guardian

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Melting Antarctic ice will raise sea level by 2.5 metres – even if Paris climate goals are met, study finds | Environment | The Guardian

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Melting of the Antarctic ice sheet will cause sea level rises of about two and a half metres around the world, even if the goals of the Paris agreement are met, research has shown.

The melting is likely to take place over a long period, beyond the end of this century, but is almost certain to be irreversible, because of the way in which the ice cap is likely to melt, the new model reveals.

Even if temperatures were to fall again after rising by 2C (3.6F), the temperature limit set out in the Paris agreement, the ice would not regrow to its initial state, because of self-reinforcing mechanisms that destabilise the ice, according to the paper published in the journal Nature.

"The more we learn about Antarctica, the direr the predictions become," said Anders Levermann, co-author of the paper from the Potsdam Institute for Climate Impact Research. "We get enormous sea level rise [from Antarctic melting] even if we keep to the Paris agreement, and catastrophic amounts if we don't."

The Antarctic ice sheet has existed in roughly its current form for about 34m years, but its future form will be decided in our lifetimes, according to Levermann. "We will be renowned in future as the people who flooded New York City," he told the Guardian.

Temperatures of more than 20C were recorded for the first time in the Antarctic earlier this year.

Jonathan Bamber, a professor of glaciology at the University of Bristol, who was not involved with the research, said: "This study provides compelling evidence that even moderate climate warming has incredibly serious consequences for humanity, and those consequences grow exponentially as the temperature rises. The committed sea level rise from Antarctica even at 2C represents an existential threat to entire nation states. We're looking at removing nations from a map of the world because they no longer exist."

Earlier this week, the earth's northern ice cap also showed the impacts of the climate crisis. Arctic sea ice reached its annual minimum, at the second lowest extent seen in four decades. On 15 September, the ice was measured at 3.74m sq km, which marked only the second time that the extent has fallen below 4m sq km in the current record, according to the US National Snow and Ice Data Center.

Scientists said the melting ice was a stark sign of how humans were changing the planet. Twila Moon, a research scientist at the University of Colorado at Boulder, said: "It's devastating to see yet another Arctic summer end with so little sea ice. Not only is there a very small area of sea ice, but it is also younger and more vulnerable overall. The Arctic is a changed place. All hope rests on humans to act on climate and slow this alarming pace of ice loss."

While the Antarctic ice sheet will take centuries to melt in response to temperature rises, the new Nature paper showed how difficult it would be to reverse.

Antarctica's vast ice cap, which covers about as much of the earth as North America and is close to three miles (5km) thick, holds more than half of the earth's fresh water. Some of it is floating sea ice, which does not cause sea level rises in the way of ice melting from land, and is subject to melting from above and below because of the warming sea.

The researchers examined how ice over land in the region can be expected to melt, and found a strong "hysteresis" effect, which makes it harder for ice to re-form than to melt. When the ice melts, its surface sinks lower down and sits in warmer air, so it requires lower temperatures for the ice to reform than it did to keep the existing ice stable.

If temperatures rose by 4C above pre-industrial levels, which some predictions say is possible if the world fails to reduce greenhouse gas emissions quickly, then the sea level rise would be 6.5 metres from the Antarctic alone, not counting the contribution from Greenland and other glaciers. That would be enough eventually to inundate all of the world's coastal cities and cause devastation on a global scale.
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Melting Antarctic ice will raise sea level by 2.5 metres - even if Paris climate goals are met, study finds

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Melting of the Antarctic ice sheet will cause sea level rises of about two and a half metres around the world, even if the goals of the Paris agreement are met, research has shown.

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Include the global heating statistics in your lessons 

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Include the global heating statistics in your lessons 

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If there were ever a time to join us, it is now. You can show your support for the Guardian today with a contribution or subscription - every form of support, however big or small, is so valuable for our future. Thank you.

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Words by Alan Evans, graphics and design by Niko Kommenda and Ben Longden

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Global heating: the vital statistics from a warming world

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If there were ever a time to join us, it is now. You can show your support for the Guardian today with a contribution or subscription - every form of support, however big or small, is so valuable for our future. Thank you.

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Amazon near tipping point of switching from rainforest to savannah – study | Environment | The Guardian

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Amazon near tipping point of switching from rainforest to savannah – study | Environment | The Guardian

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Much of the Amazon could be on the verge of losing its distinct nature and switching from a closed canopy rainforest to an open savannah with far fewer trees as a result of the climate crisis, researchers have warned.

Rainforests are highly sensitive to changes in rainfall and moisture levels, and fires and prolonged droughts can result in areas losing trees and shifting to a savannah-like mix of woodland and grassland. In the Amazon, such changes were known to be possible but thought to be many decades away.

New research shows that this tipping point could be much closer than previously thought. As much as 40% of the existing Amazon rainforest is now at a point where it could exist as a savannah instead of as rainforest, according to a study published in the journal Nature Communications.

Any shift from rainforest to savannah would still take decades to take full effect, but once under way the process is hard to reverse. Rainforests support a vastly greater range of species than savannah and play a much greater role in absorbing carbon dioxide from the atmosphere.

Parts of the Amazon are receiving much less rain than they used to because of the changing climate. Rainfall in about 40% of the forest is now at a level where the rainforest could be expected to exist as savannah instead, according to the study, led by the Stockholm Resilience Centre, based on computer models and data analysis.

Last year, Brazil's president, Jair Bolsonaro, was warned that the continued destruction of the Amazon by fire and loggers would bring the region closer to a tipping point where rainforest could turn to savannah. This year's fires in the Amazon are the worst in a decade, with a 60% increase in fire hotspots compared with last year.

There are about 3tn trees on the planet and they play a significant role in producing the oxygen we all breathe. But twice as many existed before the start of human civilisation.

Today, 10bn more trees are cut down than are planted every year. This destruction is a significant contributor to the carbon dioxide emissions that are driving the climate crisis. rees draw carbon dioxide back out of the atmosphere as they grow, and planting trees will need to play an important part in ending the climate emergency.

Forests are also a vital and rich habitat for wildlife. Earth is at the start of a sixth mass extinction event of species and the razing of forests and other ecosystems is the biggest contributor to the losses. Tropical rainforests are especially important, hosting 50% of known terrestrial species on only 6% of the world's land. Trees are also important in controlling regional rainfall, as they evaporate water from their leaves.

In urban areas, the shade from trees has been shown to both cool city streets and reduce levels of air pollution. They can also boost people's wellbeing as part of green spaces, with research showing a two-hour "dose" of nature a week significantly improving health.

Thank you for your feedback.

Arie Staal, lead author of the study, said the ecology of rainforests meant that although they effectively produce their own self-sustaining rainfall in the right climate, they are also prone to drying out in the wrong conditions.

"As forests grow and spread across a region, this affects rainfall," he explained. "Forests create their own rain because leaves give off water vapour and this falls as rain further downwind. Rainfall means fewer fires leading to even more forests."

But if large areas of rainforest are lost, rainfall levels in the region decline accordingly. This reduced level of "atmospheric moisture recycling" was simulated in the computer models used in the study.

"Drier conditions make it harder for the forest to recover and increase the flammability of the ecosystem," Staal told the Guardian. Once rainforest has crossed the threshold and converted to an open savannah-type mix of wood and grassland, it is unlikely to revert naturally to its former state.

"It is harder to return from the 'trap' caused by the feedback mechanism in which the open, grassy ecosystem is more flammable, and the fires, in turn, keep the ecosystem open," he said.

The team of researchers ran computer simulations of where forests might be expected to exist across the earth's tropical regions, given certain climatic conditions, and looked at the minimum and maximum areas of likely forest cover.

They also looked at what was likely to happen if greenhouse gas emissions kept rising, and found that the ability of forests to grow back once trees were lost would be much reduced.

Ingo Fetzer of the Stockholm Resilience Centre, co-author of the paper, said: "We understand now that rainforests on all continents are very sensitive to global change and can rapidly lose their ability to adapt. Once gone, their recovery will take many decades to return to their original state. And given that rainforests host the majority of all global species, all this will be forever lost."

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Amazon near tipping point of switching from rainforest to savannah - study

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Climate crisis and logging is leading to shift from canopy rainforest to open grassland