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Current Climate Change And The Future Of Life On The Planet

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What Sea Level Rise?

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Last week the science community was shocked by the claim that 42% of the sea-level rise of the past decades is due to groundwater pumping for irrigation purposes. What could this mean for the future - and is it true?
The causes of global sea level rise can be roughly split into three categories: (1) thermal expansion of sea water as it warms up, (2) melting of land ice and (3) changes in the amount of water stored on land. There are independent estimates for these contributions, and obviously an important question is whether their sum is consistent with the total sea level rise actually observed.

foto (c) Stefan Rahmstorf 2012

In the last IPCC report (2007), the time period 1961-2003 was analysed in some detail, and a problem was found: the individual contributions summed up to less than the observed rise - albeit with rather large uncertainties in the estimates. In the years since then, much research effort has been devoted to better quantify all contributions. For the last decade there is also improved observation systems, e.g. the GRACE satellite mission and thousands of autonomous ARGO floats monitoring globally the warming ocean.

Last year Church et al. (2011) provided a new sea-level budget analysis (see Fig. 1). For the period 1972-2008 the budget is closed, with a total rise of about 7 cm. A bit over half of that is due to melting land ice, and a bit less than half due to thermal expansion. Land water storage makes a small negative contribution, because the water stored in artificial reservoirs (which lowers sea level) is estimated to be larger than the amount of fossil groundwater pumped up for irrigation (which mostly ends up in the sea). Also for the shorter recent period 1993-2008 (for which we have satellite measurements of global sea level rise, found to be about 3 mm per year) John Church and colleagues successfully closed the sea level budget. Granted, the uncertainties in the estimates are still significant so the issue cannot be considered completely resolved. Nevertheless, the Church et al. paper defines the current state of the art against which all further studies need to measure up.

Fig. 1. Sea level rise for 1961-2008. On the left the individual contributions are shown, on the right the sum of these contributions (red) is compared to the measured rise (black). Graph from Church et al. (2011)
The groundwater shock
On May 20, Nature Geoscience published a Japanese model simulation of global land water storage (Pokhrel et al. 2012), which surprised the expert community with the conclusion that 42% of sea level rise (about 3 out of 8 cm) over the period 1961-2003 is due to reduced land water storage. In contrast to earlier studies, reservoir storage was assumed to be smaller, but mainly groundwater pumping was calculated to be several times larger.

Are the new numbers realistic? I and many colleagues I spoke to have serious doubts. It is a model result which is in stark contradiction to data-based estimates. The simulation is based on a simple assumption: first the total water demand was estimated, second the availability of near-surface water, and then the shortfall was assumed to be completely supplied by unlimited use of fossil water. The realism of this assumption is debatable - to me it seems to run a risk of greatly overestimating the withdrawal of fossil water.

The uncertainties also need to be discussed: the fossil water withdrawal is estimated by subtracting two large, uncertain numbers. Yet there is no proper uncertainty analysis. Instead, a single number with three significant digits is presented (359 km ³ per year for 1950-2000). That is almost five times the rate of 82 ± 22 km ³ per year computed by Konikow (2011) for 1961-2008, based on data for groundwater usage and actual observations of water-level declines in aquifers being depleted. Leonard Konikow, a hydrologist with the US Geological Survey, says about the huge amount of groundwater depletion simulated by Pokhrel: "Groundwater hydrologists would have noticed if such a large volume of water were 'missing'".

A bit dubious is also the fact that for the largely overlapping period 1950-2000 Pokhrel et al. find that less than 20% of sea level rise is due to land water storage, not 42% as for 1961-2003. Yadu Pokhrel responded to my query that this is due to a large short-term increase in the landwater contribution to sea level between 2000 and 2003, combined with the fact that their rates are computed simply from the difference between the end points (2003 minus 1961). 2003 happened to be a drought year with little water stored on land. Church et al. compute their budgets based on linear trends, which is more robust by using all data points and not just the end points.

Pokhrel et al. don't even mention the Church et al. paper (although that was published before their paper was submitted). They relate their discussion to the old IPCC finding of "missing sea level rise", claiming to now have found the source of this missing water. The media largely followed this story line.
Impact on future projections
If the Pokhrel numbers were right, what would this mean for the future? There are two methods to estimate future sea level rise: complex process-based models, which try to compute all individual contributions (e.g. glacier melt) under changing climate conditions, and semi-empirical models, which exploit the observed relationship between global temperature and sea level and are calibrated with past data (see my article Modeling sea level rise at Nature Education). Both have their problems and limitations, and currently I don't think anyone can seriously claim to know which will turn out to be closer to the truth.

Fig. 2. Change in sea level in mm per year due to the contribution of groundwater pumping (black curves - estimated based on data by Konikow 2011 and Wada et al. 2010) and water storage in artificial reservoirs (blue - this contribution is negative, i.e. lowers sea level). From Rahmstorf et al. (2011).

For the process-based models, the high fossil water pumping rates according to Pokhrel would simply have to be added to the projections (artificial reservoirs are generally thought to not offset much of this in future, because reservoir construction is well past its peak and there is not much scope for a large expansion). Last year we published simple projections of the groundwater pumping contribution (Rahmstorf et al. 2011, see Fig. 2), based on the data by Konikow (2011) and an earlier study by Wada et al. (2010) together with the medium UN global population projection. In the upper of the two curves, groundwater pumping raises sea level by 10 cm by 2100. If, based on Pokhrel, we assume groundwater pumping rates that are roughly twice as high, this could add 20 cm to sea level. Very recently, a new study by Wada et al. (2012) gave a more detailed projection up to 2050 which lies in between our two curves. By 2050 they find 2-4 cm sea level rise due to groundwater pumping. If the rate did not increase any further after 2050, this would add up to 5-8 cm by 2100. Whether 5, 10 or 20 cm - it is clear that groundwater pumping is a factor that must be accounted for in future sea level projections.

The impact of groundwater pumping on semi-empirical projections is smaller, because here we have two partly compensating effects. On one hand there is the added water as just discussed, on the other hand the climate-related part of the projection gets smaller, since the climatic effect on past sea level rise is also smaller, which affects the calibration of the model. In our paper we found that accounting for groundwater depletion according to Wada (i.e. upper curve of Fig. 2) lowers the projections for a moderate global warming scenario (RCP4.5) by 6 cm. If we assume again that Pokhrel's numbers are roughly twice as high as this, also for the future, then our best estimate for this scenario would come down to 91 cm sea level rise, as compared to 98 cm in our 'default case' (for which we used the lower curve of Fig. 2, based on the Konikow data).

Overall, accounting for the Pokhrel landwater estimates would thus tend to increase the process-based sea level projections and lower the semi-empirical projections, thereby reducing the discrepancy between the two - in my view a very welcome feature. But do I believe it?
Weblink
PIK sea level pages (publications, data, graphs, animations and more)
References
Church, J.A. et al (2011) Revisiting the Earth's sea-level and energy budgets from 1961 to 2008, Geophys Res Lett 38, L18601, doi:10.1029/2011GL048794

Konikow LF (2011) Contribution of global groundwater depletion since 1900 to sea-level rise. Geophys Res Lett 38:5. doi:10.1029/2011gl048604

Pokhrel, Y.A. et al (2012) Model estimates of sea-level change due to anthropogenic impacts on terrestrial water storage. Nature Geoscience, doi:10.1038/NGEO1476

Rahmstorf, S, Perrette, M & Vermeer, M (2011) Testing the robustness of semi-empirical sea level projections. Clim. Dynam. 97, 1-15, http://dx.doi.org/10.1007/s00382-011-1226-7

Wada Y, van Beek LPH, van Kempen CM, Reckman J, Vasak S, Bierkens MFP (2010) Global depletion of groundwater resources. Geophys Res Lett 37:L20402. doi:10.1029/2010gl044571

Wada, Y et al (2012) Past and future contribution of global groundwater depletion to sea-level rise. Geophys Res Lett 39, L09402, doi:10.1029/2012GL051230

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Last week the science community was shocked by the claim that 42% of the sea-level rise of the past decades is due to groundwater pumping for irrigation purposes. What could this mean for the future - and is it true?

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Earth Strike Back!

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Not long ago, a major newspaper in England ran a feature article with this bold headline: "Is this the end of the world? Earthquakes. Hurricanes. Floods. What is happening to our planet?" The article referred to three major hurricanes that devastated New Orleans and much of the Gulf Coast of America in 2005. It cited deadly heat waves and droughts, and the huge tidal wave that swept across the Indian Ocean leaving a trail of death and destruction.

The author reeled off a string of global calamities: "The sea is turning to acid, the air is choking us, the polar ice caps are melting. Famine, pestilence and plague used to be dread words from the Bible; now they are reasons for compassion fatigue... No wonder some people believe we are living in the End Times." The article described how 200 leading scientists had warned British Prime Minister Tony Blair that " global calamity was closer than ever because of climate change." The writer admitted, "Even those of us who are less convinced that the end is absolutely nigh do watch the news, read the papers or flee the latest natural disaster and wonder what on earth is happening to our planet. Is this the beginning of the end?" ( The Independent on Sunday, October 16, 2005).

On February 2 of this year, the Intergovernmental Panel on Climate Change, a United Nations body of scientists and members from 113 countries, released its "Climate Change 2007" report, forecasting that temperatures and sea levels will continue to increase "for centuries." The panel predicted sea levels to rise between 7 and 30 inches by the end of the century, and temperatures to rise 2 to 11 degrees Fahrenheit.

Is something ominous and extraordinary really happening on this earth, or are concerns about climate change nothing more than partisan fears unsupported by facts? Have we entered a unique and unprecedented time in the history of our planet, or are we merely witnessing extremes of nature that fall within the normal range? Is the earth, long abused by human development, now striking back?

Today, many sense that big changes are occurring around the globe, yet few realize there is a unique source that explains the real significance of world events. While scientists can record facts, they can only speculate about the future. The Bible, however, contains dozens of prophecies that reveal what conditions will be like at the end of this age, just before the return of Jesus Christ. Jesus told His disciples to watch for a series of events that would mark this crucial turning point in history. Are global environmental conditions actually beginning to resemble long-pondered Bible prophecies?

Decades of Warnings

Concerns about a perceived link between dramatic environmental events, global climate change and the future of human civilization are neither new nor surprising. Dr. Paul Ehrlich, professor of biological sciences at Stanford University, has written: "The dire environmental dangers our civilization faces are certainly no secret... For decades, environmental scientists have warned of interconnected environmental trends, such as loss of plant and animal diversity, rapid climate change, and the spread of toxic chemicals over the earth, that, unless reversed, could ultimately bring down our civilization" ( One with Nineveh, p. 7). Ehrlich quotes a 1993 report by 58 academies of science: "The magnitude of the threat... is linked to human population size and resource use per person... As human numbers further increase, the potential for irreversible changes of far-reaching magnitude also increases" ( ibid., p. 8).

While serving as chairman of the Council on Environmental Quality during the Carter administration, Yale forestry professor Dr. James Speth was among those sounding an alarm regarding threats to the global environment. More than 25 years ago, Speth collected scientists' alarming reports about anticipated global climatic disruptions-reports that have proved startlingly accurate. Speth and others began to see "a new agenda of global environmental challenges more threatening and difficult than the predominantly domestic concerns that motivated us... Climate change, devastation of ocean fisheries, deforestation in the tropics, loss of species, land deterioration, and other unwanted processes were occurring on a frightening scale and pace" ( Red Sky at Morning, p. xi).

Researcher Clive Ponting of University College, Swansea, in the United Kingdom, warns: "It is now virtually certain... that global temperatures will rise to a level never before experienced in settled societies or even in the last 100,000 years... Global warming is therefore a demonstration, for the first time on a world-wide scale, of the results of ignoring vital ecological constraints. The consequences for life, earth and humanity will be profound" ( A Green History of the Earth, p. 405). But what exactly is happening to the earth's environment to generate such serious concern from scientists?

Our Threatened Planet

The most fundamental and far-reaching environmental challenges we face today are increasing levels of planet-warming greenhouse gases like carbon dioxide, methane and chlorofluorocarbons that trap heat coming from the sun. Carbon dioxide is released from burning fossil fuels-oil, gasoline, coal and natural gas. Methane is released by the microbial decomposition of organic matter. Air conditioning systems use chlorofluorocarbons. Atmospheric concentrations of carbon dioxide have risen from pre-industrial levels of 280 parts per million (before 1750ad), to more than 380 parts per million in 2005, and ice core samples from Antarctica show that "carbon dioxide is 27 percent higher than at any other time in the last 650,000 years" ( Environment, Jan/Feb 2006, pp. 6-7). Global emissions of carbon dioxide could increase as much as 60 percent between 2001 and 2025, as populous nations like India and China continue to industrialize and acquire more gasoline-powered automobiles (Speth, p. 18). Between one-third and one-half of the world's forests have been destroyed, which adds to increasing carbon dioxide levels because trees remove carbon dioxide from the atmosphere ( ibid., p. 14).

This increase in atmospheric carbon dioxide correlates closely with increasing global temperatures. In the last 30 years, the earth has been warming by about 0.36 degrees Fahrenheit each decade, bringing earth's average temperature to the "highest since the end of the last ice age about 12,000 years ago" ( New York Times, September 26, 2006). Al Gore, former Vice President of the United States, points out in his noteworthy book, An Inconvenient Truth, that 20 of the 21 hottest years since the 1860s have occurred in the last quarter century (pp. 72-73). The effects of increased temperature are most dramatic nearer to the North and South Poles, where melting snow and ice reflect less sunlight, and the exposed land and ocean absorb more heat from the sun-amplifying the warming effect. Several recent studies show that "melting of the winter sea ice in the Arctic had accelerated enormously in the past two years, with a section the size of Turkey disappearing in just 12 months" ( The Independent, September 9, 2006).

Around the world, glaciers are melting at increasingly rapid rates. Studies indicate that thawing permafrost areas in sub-arctic regions will release methane, which has 20 times the warming capacity of carbon dioxide. Researchers see this unanticipated release of large quantities of methane as a "climate time bomb" waiting to explode, which will dramatically increase global temperatures ( Science News, September 9, 2006). Norwegian scientists have discovered that concentrations of chlorofluorocarbons-which trap heat a thousand times more than carbon dioxide-have doubled between 2001 and 2004 ( New Scientist, September 30, 2006). All this has accelerated temperature increases in the last 20 years.

One consequence of global temperatures rising, and sea ice and continental glaciers melting, is sea levels rising. As warming temperatures melt glaciers that release water into the oceans, sea levels rise. In the last century, ocean levels rose about 8 inches while the earth's temperature rose about one degree Fahrenheit ( New York Times, June 20, 2006). Scientists estimate that a three-degree rise in temperature would melt much of the float ice in the Arctic and ice shelves in the Antarctic, as well as the Greenland glacier, which could raise ocean levels several feet ( The Revenge of Gaia, Lovelock, pp. 51-53). This would inundate much of south Florida, the U.S. Gulf Coast and eastern seaboard, much of southeastern England and many low-lying islands in the Indian Ocean. Millions of people would be displaced and forced to migrate from Kolkata, Beijing and Shanghai (Gore, pp. 198-209). Rising sea levels make coastal developments and cities along tidal rivers more vulnerable to storm surges. If London were inundated and devastated by a storm surge, it could be ruined as a financial center, "which would lead to Frankfurt becoming Europe's financial center" ( The Times, August 23, 2006). Sir David King, chief science advisor to the British government, has noted that because of rising temperatures and sea levels, "The maps of the world will have to be redrawn" (Gore, pp. 196-197).

As glaciers and sea ice melt, millions of gallons of fresh water will be released into the oceans. This will dilute the salt concentration of ocean water, and could disrupt the flow of the Gulf Stream. This could have catastrophic effects on the agricultural areas of northwestern Europe. Rising temperatures are also associated with record heat waves and increasing droughts, torrential downpours and disastrous floods, as well as record-breaking storms and hurricanes. The three hurricanes that pounded New Orleans in 2005 were the largest, most intense storms ever recorded! In 2006, some of the hottest and driest conditions on record devastated farm production in Australia ( The Sydney Morning Herald, October 28, 2006). A recent report by a governmental agency in the UK predicts the earth's temperature will increase by 3 degrees centigrade (5.4 degrees Fahrenheit) by 2050, which will "cause drought and famine for 400 million people and devastate wildlife... because of lost arable land and water shortages" ( The Times, May 4, 2006). Temperature increases have already reduced the population of Emperor penguins in the Antarctic by 70 percent, as stable sea ice essential for nesting has thinned, broken apart and floated out to sea (Gore, p. 178). Rising global temperatures in recent decades have also contributed to the spread of infectious diseases like malaria and West Nile Fever to new areas ( Environment, June 26, 2006, pp. 6-7). Over the last quarter-century, some 30 new diseases have emerged-and old diseases are now surging again (Gore, p. 174).

Civilization in Danger

Scientists who project the consequences of global warming describe the future with a sobering perspective- which has remarkable biblical overtones! One scientist observes: "We are modifying physical, chemical and biological systems... [of the earth]... at faster rates, and over larger spatial scales than ever recorded on Earth. Humans have unwittingly embarked on a grand experiment with our planet... [that] has profound implications for all life on Earth... we are fast approaching many of the earth's limits. Current economic practices which damage the environment... cannot be continued without the risk that vital global systems will be damaged beyond repair" (Speth, p. 17). Cambridge University professor Martin Rees notes that "in the twenty-first century, humanity is more at risk than ever before from the misapplication of science. And the environmental pressures induced by collective human actions could trigger catastrophes more threatening than natural hazards... I think the odds are no better than fifty-fifty that our present civilization on Earth will survive to the end of the present century without a serious setback" ( Our Final Century, pp. 8, 186).

Author James Kunstler describes a series of "world-altering forces [economic, political and environmental]... that will fundamentally alter the terms of everyday life... on a scale no one has ever seen before" ( The Long Emergency, pp. 1-2). He writes: "Global warming is no longer a theory being disputed by political interests, but an established scientific consensus... [and that in addition to rising temperatures, flooding, spreading disease and desertification]... global warming will contribute to conditions that will shut down the global economy" ( ibid., pp. 8-9). In this context, Kunstler describes what scientists call an "omega point"-the point where "the vast interconnected networks of Earth's ecologies are so weakened that human existence is no longer possible" ( ibid.).

Larry Schweiger, president of the National Wildlife Federation, has warned: "Few Americans and few Washington political leaders comprehend how very little time we have left to act before we lose control of global warming. Within our children's lifetime the planet, under current rates of greenhouse gas emissions, will hit a tipping point that can trigger runaway global warming" ( National Wildlife, Aug/Sep 2006, p. 9). James Lovelock, a Fellow of the Royal Society, wrote: "Despite all our efforts to retreat sustainably, we may be unable to prevent a global decline into a chaotic world ruled by brutal war lords on a devastated Earth" (Lovelock, p. 154).

Climate Change and Prophecy

It is sobering to see how the warnings of prominent scientists and world leaders are beginning to resemble Bible prophecies that describe the end of this age and the time preceding the return of Jesus Christ. When Jesus was asked, "What will be the sign of Your coming, and of the end of the age?", He told His disciples to watch for a period of "wars and rumors of wars... famines, pestilences, and earthquakes in various places" (Matthew 24:3-7). The Apostle John pictures these same end-time events as the last three "horsemen" (war, famine and disease) that will kill a quarter of the world's population (Revelation 6:3-8). Today, scientists forecast that millions will die from climate-induced famines, and in wars over resources like water and oil (Kunstler, p. 5; Speth, pp. 18-19). Jesus called these increasingly global calamities "the beginning of sorrows" that would precede His imminent return (Matthew 24:8, 32-35). Scientists say today's climate changes are only the leading edge of more catastrophic changes coming in the future.

Jesus also predicted that before His return there would be a "great tribulation, such as has not been since the beginning of the world... and unless those days were shortened, no flesh would be saved" (Matthew 24:21-22). Is it merely a coincidence that leading scientists today are saying virtually the same thing -that rising temperatures may alter the earth so dramatically "that it will be unable to sustain life" in the years ahead? Today, as scientific studies document the increasing extinction of species, plankton and coral reefs are dying in warmer and more acidic oceans, while commercial fishing is decimating the world's fish stocks. Strikingly, the prophet Hosea warned that a time would come when "the land will mourn; and everyone who dwells there will waste away with the beasts of the field and the birds of the air; even the fish of the sea will be taken away" (Hosea 4:1-3).

The prophet Joel predicted an unprecedented drought, "the land mourns... the new wine is dried up, the oil fails... the grain is withered... the beasts groan... the water brooks are dried up" in conjunction with the "Day of the Lord"-the period leading up to Christ's return (Joel 1:2-3, 10-20; see "The Day of the Lord" on page 10 of this issue). Long ago Moses warned that disobedience to the laws of God would lead to drought and famine (Leviticus 26:14, 19-20). Is it just a coincidence that scientists now predict that climate change will turn much of the earth's productive agricultural surface into parched desert incapable of producing food?

The biblical reason for the prophesied calamities is that human beings have forgotten the laws of God-including the biochemical and ecological laws God designed to govern the functioning of our environment (Hosea 4:6). As a result, God tells us He will let us experience the consequences of breaking these fundamental laws, and that we will reap what we have sown (see Hosea 4:9; Jeremiah 2:19). Modern scientists have come to the same conclusion about global climate changes caused by human activities-that "we brought it upon ourselves" (Speth, p. 21). Today, scientists are writing about "the revenge of Gaia"-yet this is nothing new; thousands of years ago, Moses warned the Israelites that if they defiled the land, it would vomit them out (Leviticus 18:28). Yes, as was foretold, the earth is striking back! But are we doomed? Are we really facing the end of the world?

Tomorrow's World

Forecasters trying to look beyond what they see as the coming collapse of our modern civilization envision the need for a "guidebook"-written in clear and simple terms-that will enable survivors to "rebuild civilization without repeating too many of our mistakes" (Lovelock, pp. 156-158). This book should be "a manual for living well and for survival" that contains vital information about the purpose of life, our proper relationship to the earth, basic laws of health and guidelines for proper behavior ( ibid.). Modern intellectuals, who assume that no such book exists, do not realize that this essential information can be found in the Bible. Scripture states that the earth belongs to God (Psalm 24:1), and that human beings were meant to take care of it as stewards (Genesis 1:28; 2:15). When Jesus returns, He will "destroy those who destroy the earth" (Revelation 11:18) and use His saints to bring about "the times of restoration of all things"-including the environment of this earth (Acts 3:19-21). The present dramatic climate changes are not a preview of the end of the world, but rather are a prelude to a much more exciting future you can be part of- if you begin to live by what is actually in the Bible, and learn to recognize the significance of environmental changes taking place around the globe, as we approach Tomorrow's World!

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Not long ago, a major newspaper in England ran a feature article with this bold headline: "Is this the end of the world? Earthquakes. Hurricanes. Floods. What is happening to our planet?" The article referred to three major hurricanes that devastated New Orleans and much of the Gulf Coast of America in 2005.

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What is Global Warming?

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Glaciers are melting, sea levels are rising, cloud forests are dying, and wildlife is scrambling to keep pace. It has become clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than at any time in the last 800,000 years.

We often call the result global warming, but it is causing a set of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. While many people think of global warming and climate change as synonyms, scientists use "climate change" when describing the complex shifts now affecting our planet's weather and climate systems-in part because some areas actually get cooler in the short term.

Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and habitats, rising seas, and a range of other impacts. All of those changes are emerging as humans continue to add heat-trapping greenhouse gases to the atmosphere, changing the rhythms of climate that all living things have come to rely on.

What will we do-what can we do-to slow this human-caused warming? How will we cope with the changes we've already set into motion? While we struggle to figure it all out, the fate of the Earth as we know it-coasts, forests, farms, and snow-capped mountains-hangs in the balance.

Understanding the greenhouse effect

The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse, hence the name.

Sunlight shines onto the Earth's surface, where the energy is absorbed and then radiate back into the atmosphere as heat. In the atmosphere, greenhouse gas molecules trap some of the heat, and the rest escapes into space. The more greenhouse gases concentrate in the atmosphere, the more heat gets locked up in the molecules.

Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This natural greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit (33 degrees Celsius) cooler.

In 1895, the Swedish chemist Svante Arrhenius discovered that humans could enhance the greenhouse effect by making carbon dioxide, a greenhouse gas. He kicked off 100 years of climate research that has given us a sophisticated understanding of global warming.

Levels of greenhouse gases have gone up and down over the Earth's history, but they had been fairly constant for the past few thousand years. Global average temperatures had also stayed fairly constant over that time- until the past 150 years. Through the burning of fossil fuels and other activities that have emitted large amounts of greenhouse gases, particularly over the past few decades, humans are now enhancing the greenhouse effect and warming Earth significantly, and in ways that promise many effects, scientists warn.

Aren't temperature changes natural?

Human activity isn't the only factor that affects Earth's climate. Volcanic eruptions and variations in solar radiation from sunspots, solar wind, and the Earth's position relative to the sun also play a role. So do large-scale weather patterns such as El Niño.

But climate models that scientists use to monitor Earth's temperatures take those factors into account. Changes in solar radiation levels as well as minute particles suspended in the atmosphere from volcanic eruptions, for example, have contributed only about two percent to the recent warming effect. The balance comes from greenhouse gases and other human-caused factors, such as land use change.

The short timescale of this recent warming is singular as well. Volcanic eruptions, for example, emit particles that temporarily cool the Earth's surface. But their effect lasts just a few years. Events like El Niño also work on fairly short and predictable cycles. On the other hand, the types of global temperature fluctuations that have contributed to ice ages occur on a cycle of hundreds of thousands of years.

For thousands of years now, emissions of greenhouse gases to the atmosphere have been balanced out by greenhouse gases that are naturally absorbed. As a result, greenhouse gas concentrations and temperatures have been fairly stable, which has allowed human civilization to flourish within a consistent climate.

Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the Industrial Revolution. Changes that have historically taken thousands of years are now happening over the course of decades.

Why does this matter?

The rapid rise in greenhouse gases is a problem because it's changing the climate faster than some living things can adapt to. Also, a new and more unpredictable climate poses unique challenges to all life.

Historically, Earth's climate has regularly shifted between temperatures like those we see today and temperatures cold enough to cover much of North America and Europe with ice. The difference between average global temperatures today and during those ice ages is only about 9 degrees Fahrenheit (5 degrees Celsius), and the swings have tended to happen slowly, over hundreds of thousands of years.

But with concentrations of greenhouse gases rising, Earth's remaining ice sheets such as Greenland and Antarctica are starting to melt too. That extra water could raise sea levels significantly, and quickly. By 2050, sea levels are predicted to rise between one and 2.3 feet as glaciers melt.

As the mercury rises, the climate can change in unexpected ways. In addition to sea levels rising, weather can become more extreme. This means more intense major storms, more rain followed by longer and drier droughts-a challenge for growing crops-changes in the ranges in which plants and animals can live, and loss of water supplies that have historically come from glaciers.

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Glaciers are melting, sea levels are rising, cloud forests are drying, and wildlife is scrambling to keep pace.

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How You Can Stop Global Warming

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Rising sea levels. Raging storms. Searing heat. Ferocious fires. Severe drought. Punishing floods. The effects of climate change are already threatening our health, our communities, our economy, our security, and our children's future.

What can you do? A whole lot, as it turns out. Americans, on average, produce 21 tons of carbon a year, about four times the global average. Personal action is, of course, no substitute for meaningful government policies. We still must limit carbon pollution and aggressively move away from dirty fossil fuels toward cleaner power.

But it's important to remember the equally vital contributions that can be made by private citizens-which is to say, by you. "Change only happens when individuals take action," says clean energy advocate Aliya Haq. "There's no other way, if it doesn't start with people."

Here are a dozen easy, effective ways each one of us can make a difference.

1. Speak up!

What's the single biggest way you can make an impact on global climate change? "Talk to your friends and family, and make sure your representatives are making good decisions," Haq says. By voicing your concerns-via social media or, better yet, directly to your elected officials-you send a message that you care about the warming world. Encourage Congress to enact new laws that limit carbon emissions and require polluters to pay for the emissions they produce. "The main reason elected officials do anything difficult is because their constituents make them," Haq says. You can help protect public lands, stop offshore drilling, and more here.

2. Power your home with renewable energy.

Choose a utility company that generates at least half its power from wind or solar and has been certified by Green-e Energy, an organization that vets renewable energy options. If that isn't possible for you, take a look at your electric bill; many utilities now list other ways to support renewable sources on their monthly statements and websites.

3. Weatherize, weatherize, weatherize.

"Building heating and cooling are among the biggest uses of energy," Haq says. Indeed, heating and air-conditioning account for almost half of home energy use. You can make your space more energy efficient by sealing drafts and ensuring it's adequately insulated. You can also claim federal tax credits for many energy efficiency home improvements. To help you figure out where to start, you could also get a home energy audit, which some utilities offer free of charge. (Alternatively, you can hire a professional to come to your home and perform one; the Inflation Reduction Act offers a partial tax credit for this.) The EPA's Home Energy Yardstick gives you a simple assessment of your home's annual energy use compared with similar homes.

4. Invest in energy-efficient appliances.

Since they were first implemented nationally in 1987, efficiency standards for dozens of appliances and products have kept 2.3 billion tons of carbon dioxide out of the air. That's about the same amount as the annual carbon pollution coughed up by nearly 440 million cars. "Energy efficiency is the lowest-cost way to reduce emissions," Haq says. When shopping for refrigerators, washing machines, heat pump water heaters, and other appliances, look for the Energy Star label. It will tell you which are the most efficient. (There may also be rebates to earn from your purchase of Energy Star-certified products.)

And when you're ready to swap out your old machines, don't just put them on the curb: Recycling an old refrigerator through the EPA's Responsible Appliance Disposal Program can prevent an additional 10,000 pounds of carbon pollution because the global-warming pollutants in the refrigerants and foam would be properly captured rather than vented to the air.

5. Reduce water waste.

Saving water reduces carbon pollution, too. That's because it takes a lot of energy to pump, heat, and treat your water. So take shorter showers, turn off the tap while brushing your teeth, and switch to WaterSense-labeled fixtures and appliances. The EPA estimates that if just one out of every 100 American homes were retrofitted with water-efficient fixtures, about 100 million kilowatt-hours of electricity per year would be saved-avoiding 80,000 tons of global warming pollution.

6. Actually eat the food you buy-and compost what you can't.

Approximately 10 percent of U.S. energy use goes into growing, processing, packaging, and shipping food-about 40 percent of which winds up in the landfill. "If you're wasting less food, you're likely cutting down on energy consumption," Haq says. As for the scraps you can't eat or the leftovers you don't get to, collect them in a compost bin instead of sending them to the landfill where they release methane. Recycling food and other organic waste into compost provides a range of environmental benefits, including improving soil health, reducing greenhouse gas emissions, recycling nutrients, and mitigating the impact of droughts.

7. Buy better bulbs.

LED light bulbs use one-sixth the amount of energy to deliver the same amount of light as conventional incandescents and last at least 10 times longer. They're also cheaper in the long run: A 10-watt LED that replaces your traditional 60-watt bulb will save you $125 over the light bulb's life. And because the average American home has around 40 to 50 light bulbs, this is a simple swap that will reap huge rewards. If every household in the United States replaced just one incandescent with an Energy Star-labeled LED, we would prevent seven billion pounds of carbon pollution per year. That's equivalent to the emissions of about 648,000 cars.

8. Pull the plug(s).

Taken together, the outlets in your home are likely powering about 65 devices-an average load for a home in the United States. Audio and video devices, cordless vacuums and power tools, and other electronics use energy even when they're not charging. This "idle load" across all U.S. households adds up to the output of 50 large power plants in the country. So don't leave fully charged devices plugged into your home's outlets, unplug rarely used devices or plug them into power strips and timers, and adjust your computers and monitors to automatically power down to the lowest power mode when not in use.

9. Drive a fuel-efficient vehicle.

Gas-smart cars, such as hybrids and fully electric vehicles, save fuel and money. And once all cars and light trucks meet 2025's clean car standards, which means averaging 54.5 miles per gallon, they'll be a mainstay. For good reason: Relative to a national fleet of vehicles that averaged only 28.3 miles per gallon in 2011, Americans will spend $80 billion less at the pump each year and cut their automotive emissions by half. Before you buy a new set of wheels, compare fuel-economy performance here.

10. Maintain your ride.

If all Americans kept their tires properly inflated, we could save 1.2 billion gallons of gas each year. A simple tune-up can boost miles per gallon anywhere from 4 percent to 40 percent, and a new air filter can get you a 10 percent boost. Also, remove unnecessary accessories from your car roof. Roof racks and clamshell storage containers can reduce fuel efficiency by as much as 5 percent.

11. Rethink planes, trains, and automobiles.

Choosing to live in walkable smart-growth cities and towns with quality public transportation leads to less driving, less money spent on fuel, and less pollution in the air. Less frequent flying can make a big difference, too. "Air transport is a major source of climate pollution," Haq says. "If you can take a train instead, do that." If you must fly, consider purchasing carbon offsets to counterbalance the hefty carbon pollution associated with flying. But not all carbon offset companies are alike. Do your homework to find the best supplier.

12. Reduce, reuse, and recycle.

In the United States, the average person generates 4.5 pounds of trash every day. Fortunately, not all the items we discard end up in landfills; we recycle or compost more than one-third of our trash. In 2014 this saved carbon emissions equivalent to the yearly output of 38 million passenger cars. But we could be doing so much more. "Reduce should always be the number-one priority," says NRDC senior resource specialist Darby Hoover. And to reap the environmental benefits of "recyclable" goods, you must recycle according to the rules of your municipality, since systems vary widely by location. Search your municipality's sanitation department (or equivalent) webpage to learn exactly what you can place in the recycling bin, as counties and cities often differ in what they accept.
This story was originally published on April 20, 2022 and has been updated with new information and links.

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There are many ways to prevent global warming from becoming worse. Many nations have put laws into place to fight climate change -- here's what you can do.

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Things You Can Do To Prevent Climate Change

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6 Things You Can Do To Prevent Climate Change

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There are always things that we can do to fight against climate change. Discover how you can help.