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People are seeing change all over the world. Arctic sea ice is melting earlier and forming later. Glaciers are disappearing. Heat waves, storms and floods are becoming more extreme. Insects are emerging sooner and flowers are blooming earlier. In some places, birds are laying eggs before they're expected and bears have stopped hibernating.

So what's going on? Our planet is getting warmer, and even a small increase in temperature can change our climate. And when our climate changes, we're all affected.

A Natural Greenhouse

Earth is the only planet we know of that can support life. The reason Earth is different than the rest relies on a number of factors. We get just the right amount of energy from the sun (if we were any closer, we would burn up; if we were any further, we'd freeze). Our atmosphere is a layer of gases surrounding the Earth that absorbs ultra violet radiation and prevents temperatures from rising too high or getting too cold. The greenhouse effect is the process that causes the surface of the Earth to be warmer than it would be if we had no atmosphere. Without these three factors, most like on Earth couldn't exist.

The Greenhouse Effect

Natural Cycles

Several natural cycles of the Earth keep it and its atmosphere in perfect balance. Carbon is essential to life and the carbon cycle keeps it moving throughout all Earth's systems. Water is one of the most important things to our survival, and the water cycle keeps it moving around and around our Earth and atmosphere - even through our bodies.

Weather Versus Climate

Weather is what's happening with the atmosphere that surrounds us. It's not the same as climate, which refers to the pattern of weather we expect to see in a particular place. The weather is always driven by the sun's energy, whether it's warm outside or snowing due to the circulation of warm air to cold places and cold air to warm places by the atmosphere. This, combined with the movement of the oceans and the amount of moisture in the air creates everything from perfect sunny days to terror-filled tornadoes.

Even though the weather changes frequently, the climate of a particular place should always be about the same. In Alaska, for example, there shouldn't be any tropical-like weather. In California, it shouldn't snow too much in the winter.

The fact is, while the Earth's climate has changed many times over millions of years (ice ages, for example, happen naturally every 100,000 years or so), it really shouldn't be changing much during any one person's lifetime. We're still recovering from the last ice age, which is said to have wiped out the dinosaurs. While temperatures do rise gradually over time after an ice age, today our planet's surface temperatures seem to be rising faster now than they were 100 years ago. And this is what has many people worried.

Balancing Act

Our planet is always changing and its systems are constantly working together to keep a kind of balance. All forms of life, including humans, depend on this balance for their existence.

All living things are connected to each other in ecosystems by food chains and food webs. Plants get energy from the sun. Herbivores (species that don't eat meat) get energy by eating plants. Carnivores (that eat meat) get energy by eating herbivores. This is how energy flows through all ecosystems - starting from the sun.

When any one part of an ecosystem chain breaks, the survival of the entire system, along with every living thing that depends on it for survival, hangs in the balance. For example, if someone decides to spray a poisonous pesticide on plants to keep bugs from eating them, then lizards may accidentally ingest that poison when they eat the plants and cats may be poisoned, too, when they catch and eat the lizards. With no cats around, the rat population could explode - and rats carry diseases that are even more dangerous for humans.

Another example is when a volcano erupts. If the eruption is very big, it could do a lot of damage besides killing thousands of people. A volcanic eruption spreads huge amounts of ash and gases into the atmosphere and around the globe, which could cause temperatures worldwide to fall. And when temperatures change dramatically like this, it affects crop patterns and could lead to massive food shortages.

Temperature Rising

Whether you believe in global warming or not, the fact is that the 11 hottest years recorded in the last 100 years have all happened after 1995. The world is definitely getting warmer.

When the world's temperatures get warmer, a few things happen. The water cycle speeds up, causing more rain, droughts, wildfires and extreme heat waves. There will be more greenhouse gases in the air, as the atmosphere reaches capacity of how many gases it can absorb. Arctic ice will melt sooner and faster and won't be as thick or expensive when it reforms. The oceans will warm and cause sea levels to rise more quickly, which can cause flooding on land and water contamination. Glacier ice will melt.

Greenhouse Gases

These gases help keep the world from being too hot or too cold. But the amounts of some greenhouse gases in the atmosphere are increasing, making our planet warmer. Greenhouse gases include water vapor (mostly natural source), carbon dioxide (mostly human source), methane (mostly human source) and nitrous oxide (mostly human source).

Far North & South

The most global warming has been seen in the Earth's coldest places, like the Arctic, Antarctica, Alaska and parts of Canada, Scandinavia and Russia.

Arctic temperatures are rising twice as fast as anywhere else on Earth. There has been a huge amount of ice loss in the last 20-30 years. While some is natural, global warming seems to be the main culprit. Ice shelves that have been around for tens of thousands of years have collapsed due to lower temperatures, which causes sea levels to rise. Permafrost has started to melt, which results in forests and even towns and cities to crumble as the ground beneath them thaws.

Because the far north and south have very fragile ecosystems, when one part of the chain breaks the effects can be seen almost immediately. As the ice disappears, so are tiny sea creatures called krill are dying - and so are the many fish, birds and whales that eat them. Polar bears spend most of their time on sea ice hunting seals and other sea animals. As the ice melts, the bears' hunting season is shortened and female bears, with lowered body weights, can't seem to produce cubs. Warmer summers also mean certain pests' life cycles are longer than before. For example, the spruce bark beetle, which is only supposed to live for one summer, is now surviving for two. This tiny bug destroys an unimaginable number of trees in Arctic forests - and now it can do it two years in a row instead of just one.

Polar Bear on floating ice

The World Ocean

Most of the Earth's surface is covered by a single ocean. All forms of life - even those that don't actually live in the ocean itself - depend on it for survival. For example, our ocean helps control the Earth's temperature with its currents, by constantly keeping cold and warm water moving. Ocean water dissolves lots of substances, including carbon dioxide gas. All ocean creatures and even sea birds depend on microscopic plankton - tiny plants that take in carbon dioxide to grow - for food and survival.

But when the ocean warms (which it has been), it can't dissolve as much carbon dioxide, plankton can't survive and the currents change (which greatly affects the weather and other things on dry land). Also, the sea level rises, so certain islands that are currently above water may actually disappear in the next 100 years.

The effects of global warming on things that live in the ocean are massive. We already talked about plankton, but what about other species? Coral reefs - home to many ecosystems and living creatures - can die as water temperatures rise. Sea turtles depend on beaches to lay their eggs, but many beaches are disappearing thanks to rising sea levels. Whales, who depend on krill who depend on plankton, die. Fish stocks fall, translating into food shortages for humans.

Where is global warming going?

We All Live On Land

What changes are we seeing on land as a result of global warming? We're seeing longer periods of drought, more wildfires, growing deserts (which can't support farming), glacier melt and deforestation. In fact, every second a chunk of forest the size of a football field is cut down or burned somewhere in the world.

In terms of living things, the effects of global warming are causing huge changes and disruptions. Plants and insects are moving upward (north) and causing distress to the natural, original ecosystems of those areas. Birds are also moving further north and some are even laying their eggs earlier, which can be a problem when it's out of sync with insect hatchings (since birds are insects' main predators). The winter of 2006 was so warm that mountain bears in Spain decided not to hibernate (sleep for the winter).

And what about us humans? How does and will global warming affect us, our lives and our survival as a species? First off, all human needs fresh water to survive. But changing rainfall patterns and melting glaciers will cause severe droughts, during which crops will fail, causing huge food shortages. We can also expect more heat waves. In 2003, Europe experienced such an extreme spell of hot weather that more than 20,000 people died as a direct result of the heat. Also, mass extinction of many other species we depend on for survival will mean big trouble for humanity.

Our Energy Use

There is no doubt that it's our own fault the world's temperature is rising and global warming is happening. We depend too much on fossil fuels that release deadly amounts carbon dioxide into the atmosphere. We need to start considering alternative sources of energy quickly, like nuclear, solar and wind. We cut down trees, which use carbon dioxide in their natural life cycles, so less of the poisonous gas can be absorbed naturally.

Humans are high energy consumers. Every day, we each exhale 1 kilogram (2.2 pounds) of carbon dioxide into the air. We keep ourselves warm in cold places by burning huge amounts of fuel. We use tons of energy pumping, cleaning, heating and then disposing of water. The food we eat is a huge source of greenhouse gases: fossil fuels used in fertilizers and farm machinery, food processing, transportation, packing and cooking. Construction requires all kinds of building materials that can only be made with massive amounts of energy. Our major sources of transportation are huge consumers of energy - ships, jets and cars. Electricity isn't captured magically - it takes the burning of massive amounts of fossil fuel to convert energy into electrical current. And all the "things" in your life - clothes, cell phones, toothbrushes, etc. - are made using energy... and so are the packages all these things come in.

You CAN Help!

The problem seems so big, it may be hard for you to imagine that anything you do can really help at all. But it will. Here are some changes you can make in your life to help prevent global warming:

Plant trees

Start a seed bank (keep the seeds of many varieties of plants stored away safely)

Switch every light in your house to an energy-saving bulb

Reduce, reuse, recycle

Wear a sweater instead of turning up the heat in your house

Wear lighter clothing when it's hot instead of turning on a fan

Turn lights, computers and all your chargers off and unplug them when they're not in use

Only do full loads of laundry

Take shorter showers

Skip the car ride and use your bike, or walk or take the bus

Don't buy bottled water; drink tap water, and filter it if you like

Eat lower on the food chain (less meat) and eat fewer processed foods

Knowledge is power. Change can only happen if all of us read about, listen to and discuss what's happening in the world today.

Planet Power

If scientists are right, each one of us is at least a little bit responsible for global warming. So each of us has to decide what we're going to do about it, and what kind of world we want to live in.

Our planet has been around for almost 5 billion years. It's gone through so many changes during that time - global warming may be the Earth's next big change.

No matter what changes lie ahead, our planet isn't going anywhere. And neither are we. But what we do now could have a big effect on what our lives could be like in the near future. This is our planet - let's make sure in the future it stays as wonderful a place to live in as it is now.

Related Stories:

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We are seeing change all over the world. Arctic sea ice is melting earlier and Glaciers are disappearing. Heat waves and storms are becoming more extreme. Learn all about Global Warming on Kidzworld!

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Earth's warming threatens to tilt populations of an unusual reptile so dramatically that the species' long-term survival could be put in peril. The change could leave the species, a survivor from the age of the dinosaurs, without enough females to avoid extinction.

The tuatara (TOO-ah-TAAR-ah) is about the size of a squirrel. A crest of floppy white spikes runs down its back. Although it resembles a lizard, the grey-green species ( Sphenodon punctatus) actually belongs to a separate and distinct reptile order. (An order is that place on the tree of life directly above species, genus and family).

There are four orders of reptiles. Three have many distinct species. Not so the Rhynchocephalia (RIN-ko-suh-FAY-lee-uh). This order holds on with just a single member: the tuatara.

That wasn't always true. More than 200 million years ago, different rhynchocephalians could be found across much of the globe. Alas, most of these ancient reptiles died out around 60 million years ago, along with the last of the dinosaurs. Today, their descendants inhabit several dozen islands and fenced nature reserves, all in New Zealand.

And these animals are unique. For instance, unlike other reptiles, which have one row of teeth in its upper jaw, the tuatara have two parallel rows. As the animal chews, its bottom single row of teeth slots neatly in between the top two rows. The tuatara also have extra, rib-like bones, called gastralia (or "belly-ribs").

Humans introduced rats and other mammals to New Zealand, in the South Pacific. For centuries, these animals have threatened the survival of the island nation's unusual reptiles ( see Explainer). Although tuatara have survived that catastrophe, they now face a new threat: too few females. One reason: With global warming, their island homes are becoming way too hot!

Temperature sensitive

For all of its oddities, in one important way the tuatara resemble many of their reptile cousins: Whether an individual hatches from its egg as a male or a female depends on the temperature at which that egg had incubated.

Mom doesn't sit on her eggs. She just digs a nest in the ground and then leaves her eggs to develop. Cooler temperatures produce more girls; warmer temperatures, more boys. But with global warming, average temperatures across New Zealand have been increasing. And more male tuatara will hatch.

Adding to the problem, females don't seem to do well when males greatly outnumber them. Already on at least one island, the local population of tuatara risks dying out. There, guys outnumber gals by more than 2-to-1, according to a study published April 8 in the scientific journal PLOS ONE.

For a long time, scientists didn't realize the impact that temperatures can have on these reptiles. Then, in 1992, Alison Cree discovered something odd. Cree is a zoologist at New Zealand's University of Otago. She and her students needed to know the sex of some tuatara that had been born in captivity. And that required surgery.

Outwardly, young tuatara males look just like females. To tell them apart, scientists must cut a tiny slit through the animal's skin. Only then can experts peer inside to see whether the reptile has ovaries or testes. A female's ovaries make eggs. A male's testes produce the sperm needed to fertilize those eggs.

All of the eggs deposited by a mom into one nest are a clutch. And Cree noticed that one clutch of seven tuatara from a New Zealand zoo were all boys. That made her suspicious.

She knew scientists had incubated the eggs in a cupboard that sometimes got warm. Could the all-male clutch reflect the influence of temperature? That certainly happens in some other reptiles, including crocodiles, alligators and most turtles. Yet extra warmth wouldn't necessarily mean more males. In many of those species, eggs incubated at the highest temperatures produce mostly females.

Alison Cree, University of Otago

So Cree's team incubated tuatara eggs at different temperatures. And these experts confirmed that eggs kept at warmer temperatures hatched more males.

This is completely different from the way sex is decided in mammals, including people. In them, chromosomes determine a baby's sex. A human embryo always inherits an X-chromosome from its mother. Its dad - as all men - have an X- and a Y-chromosome. If the baby inherits an X-chromosome from dad, she will be a girl. If the baby instead gets one of dad's Y-chromosomes, he will be a boy.

But tuatara don't have X- or Y-chromosomes. When a tuatara mother first lays a fertilized egg, the embryo inside is neither male nor female. In this species, temperature tends to determine how many hatchlings emerge as guys or gals. And just a small difference in nest temperature can make a difference. For example, 95 percent of eggs kept at a constant temperature of 21.2°Celsius (70.2°Fahrenheit) will develop into females. The ratio flips for eggs incubated a little more than one degree warmer - at 22.3 °C (72.1 °F). Now, 95 percent emerge as males.

That sensitivity to such minor swings in temperature has set off alarms among scientists working to ensure the tuatara's survival. They know that climate scientists have calculated that temperatures in New Zealand could rise by as much as 4 °C (7.2 °F) by 2080. According to the new PLOS ONE study, on at least one island where the reptiles now live - North Brother Island - such a large temperature increase would mean no more female tuatara. And, eventually, that would result in no more tuatara. Period.

Andrew McMillan/Wikimedia Commons

Bad times on North Brother

This wind-battered island is a mere 4 hectares (roughly 10 acres) in size. It's home to an old lighthouse and several hundred tuatara. And here, roughly seven out of every 10 of the reptiles are males.

Nicola Mitchell is a biologist at the University of Western Australia and co-author of the new study. She and her colleagues now estimate that at today's temperatures, 56 percent of tuatara eggs on North Brother Island should become males. That's far fewer than the real number. So Mitchell suspects the tiny island's shortage of females must be due to more than just climate change. Something else must be helping tilt the ratio in favor of males.

And it may be the males' behavior.

Her team has noticed that tuatara on North Brother have been getting skinnier over the past few decades. But females have slimming faster than males. One reason could be that males chase and harass females they try to get to mate with them. (With few females, each gal may find herself getting far more attention than she wants.) The males also are generally larger and more aggressive than the females. So the guys may be better than females at staking a claim to prime territory and food.

The end result is that the North Brother females have become slow to reproduce. Healthy females normally lay eggs every two to five years. But North Brother's gals only lay eggs once every nine years or so. Observes Mitchell, "We've got higher mortality in females and lower reproductive rates." Project this trend out into the future and within 150 years "there would only be males," she says.

Indeed, all signs suggest the North Brother population is slowly collapsing. "You can see this spiraling pattern and it's all heading in the wrong direction," says Nicola Nelson. Another member of the tuatara research team, she works at Victoria University of Wellington, New Zealand.

Nelson says that it's possible the island is just too small and barren for tuatara to survive there forever. Maybe its colony is destined to die out. But many other tuatara populations also live on tiny islands. By monitoring the struggling group on North Brother, researchers are now learning what can happen when males start to greatly outnumber females.

Seeking shade

One question that scientists still haven't answered is whether tuatara mothers could change their behavior to match a new climate. After all, they've survived other swings in temperature over the species' long history. It is certainly possible the reptiles could shift where they lay their eggs or when. That would help them to avoid soil that is too warm.

This seems to be true for at least some other reptiles that have their sex set by egg temperature. Among them is the painted turtle, notes Jeanine Refsnider. She is an ecologist at the University of California, Berkeley.

Painted turtles are a common sight in rivers and lakes across the United States. Among these colorful creatures, more females hatch when temperatures are higher. However, they sometimes adjust to change, Refsnider notes.

"Normally they nest out in sunny, open habitats," she says. "I found that if you expose turtles to warmer temperatures than they are used to, they choose shadier spots to nest."

But shade is not always available. One group she studied lived in the desert. For those turtles, there just weren't any shade in which to nest.

Such a limit could endanger other reptiles living in small areas where there is little choice about where to lay eggs, Refsnider says. After all, she notes, "Reptiles don't migrate like birds."

Jeanine Refsnider, University of California, Berkeley

Other reptiles indeed could end up with either too many males or too many females in a warming world, points out Fredric Janzen. He is an ecologist at Iowa State University in Ames. While unfortunate, he notes, such changes could warn of potential threats facing other species.

The reptiles "may serve as the 'canaries in the coal mine' for all species with key parts of their biology affected by temperature," says Janzen. Coal miners used to take caged canaries into the mines. When levels of toxic gases began to rise, the birds would have trouble breathing - or die. This would signal to the miners that they must flee to safety or risk a similar fate. Today, scientists liken many environmental warning signs to those old mine canaries.

Moving south

The tuatara could migrate to cooler climes - but only with help from people.

Part of New Zealand's long-term plan for looking after tuatara is to return them to places they lived before humans arrived. Old tuatara bones have been found up and down the two larger islands that make up New Zealand's mainland, from the warm tip of the North Island right down to the cool far end of the South Island.

Right now, tuatara live mostly on small islands off of the North Island. Cree says that moving some tuatara back into different types of habitat, including cooler areas, should ensure the species can survive.

With that in mind, scientists released 87 tuatara into the South Island's Orokonui Ecosanctuary in early 2012. More than 8 kilometers (5 miles) of steel fence surrounds the sanctuary. The high fence keeps out any mammals that might view the reptiles as lunch. Temperatures too are milder there - around 3 °C (5.4 °F) cooler on average than on the islands where tuatara now live.

Scott Jarvie, University of Otago

In fact, many potential nesting sites at Orokonui appear too cool to produce boys. Still, climate scientists predict that before the end of the century, even Orokonui will be as warm as Stephens Island, where tuatara now flourish. "That's within the lifespan of a tuatara," Cree says. These reptiles can live for at least 80 years and likely more than 100 years.

So moving tuatara into lots of new habitats is like an insurance policy. "We were down to 32 populations," says Nelson. "now we're up to 45 populations of tuatara in lots of different locations. We've certainly got our eggs in more baskets."

That's a good thing, since the tuatara face other future challenges as well. Drought likely will increase in some areas of its range. That can destroy eggs and kill hatchlings. And sea level rise will shrink the island territory available for this reptile to inhabit. "It's climate that's changing, not just temperature," explains Cree.

For now, wherever tuatara live under protection, the reptiles are thriving. Scientists already have found two tuatara nests at Orokonui. Their eggs should hatch this year. Those babies will be relatively safe in their sanctuary, but likely see many changes over the course of their very long lives.

Power Words

behavior The way a person or animal acts towards others, or conducts itself.

chromosome A single threadlike piece of coiled DNA found in a cell's nucleus. A chromosome is generally X-shaped in animals and plants. Some segments of DNA in a chromosome are genes. Other segments of DNA in a chromosome are landing pads for proteins. The function of other segments of DNA in chromosomes is still not fully understood by scientists.

clutch (in biology) The eggs in a nest or the hatchlings from that collective group of eggs.

ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

embryo A vertebrate, or animal with a backbone, in its early stages of development.

gastralia Bones nicknamed "belly ribs" that are only found in tuatara, crocodiles and alligators. They support the abdomen but are not attached to the spine.

hatchling A young animal that recently emerged from its egg.

mammal A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding the young, and (typically) the bearing of live young.

New Zealand An island nation in the southwest Pacific Ocean, roughly 1,500 kilometers (some 900 miles) east of Australia. Its "mainland" - consisting of a North and South Island - is quite volcanically active. In addition, the country includes many far smaller offshore islands.

order (in biology) It is that place on the tree of life directly above species, genus and family.

reptile Cold-blooded vertebrate animals, whose skin is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles.

sperm In animals, the male reproductive cell that can fuse with an egg of its species to create a new organism.

testis (plural: testes) The organ in the males of many species that makes sperm, the reproductive cells that fertilize eggs. This organ also is the primary site that makes testosterone, the primary male sex hormone.

tuatara A reptile native to New Zealand. The tuatara are the sole remaining species of one of the four orders of reptiles.

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Earth's warming threatens to tilt populations of an unusual reptile so dramatically that the species' long-term survival could be put in peril. The change could leave the species, a survivor from the age of the dinosaurs, without enough females to avoid extinction. The tuatara (TOO-ah-TAAR-ah) is about the size of a squirrel.

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A polar bear walks along a rocky shore, looking for food. The bear would usually be on the sea ice hunting for seals, pouncing when the seal comes up to breathe. But the ice has started to melt earlier and re-form later than it has in the past. Without the sea ice, the polar bear must scavenge for other, less nutritious food.

These changes in polar sea ice are a result of climate change. But this isn't just affecting polar bears-climate change affects everyone.

What is climate change?

Weather changes day to day-sometimes it rains, other days it's hot. Climate is the pattern of the weather conditions over a long period of time for a large area. And climate can be affected by Earth's atmosphere.

Our Earth is surrounded by an atmosphere made up of gases. When sunlight enters our atmosphere, some of the sun's heat is trapped by the gas, and some bounces back out into space. By trapping that heat, our atmosphere keeps Earth warm enough to live on. Without it, our planet would be very cold, like Mars.

Earth's climate has always naturally cycled through change, caused by how much of the sun's energy was absorbed by the atmosphere. In fact over the past 650,000 years, the Earth has gone through seven ice ages and warming periods.

What's different now?

But during the past few hundred years, oil, gas, and coal have powered homes, cars, and factories. These energy sources release a gas called carbon dioxide (CO2) into the atmosphere. This gas traps heat that would otherwise escape Earth's atmosphere. That increases Earth's temperature, which contributes to the planet's warming.

That's why many scientists agree that the Earth is now warming because of human activity. How do they know? Through careful study, they know that the climate is warming about 10 times faster than the average previous warming times. They've also ruled out the natural factors that caused warming in the past.

The Earth's average temperature has increased about 1.5°F in the past hundred years. It doesn't sound like much, but scientists think that the temperature increase has caused melting glaciers, drought, and coral reef die-off. (Coral can't survive in water that's too warm.) They expect the climate will warm another .5°F to 8.6°F by the year 2100.

What could happen?

Climate change affects more than temperature. Warmer water changes the patterns of ocean currents, affecting global weather patterns.

Some places will receive more rainfall, which could lead to flooding, while other places will get less, which might mean drought. Tropical storms could be stronger, and a continuing rise in sea level due to melting polar ice might push people out of their homes.

Hundreds of plant and animal species have already experienced changes because of climate change. The American pika, for example, is a small mammal that lives in cool mountainous areas in western North America-in fact, it can die when exposed to temperatures warmer than 78˚F. So as the mountain climate heats up, the pika climbs the slopes in search of cooler habitat. But what happens when temperatures at the top become too warm for the pika?

Other species will benefit from a warmer world-but in some cases that would be bad news for humans. Because disease-carrying mosquitoes thrive in warm, wet weather, more people could contract illnesses such as malaria as the Earth warms.

What can we do about it?

You can do a lot! It's simple to make a difference to keep the Earth healthy. Try some of these tips to reduce the amount of carbon dioxide you add to the atmosphere.

Instead of traveling in a car, use public transportation, walk, or ride your bike when you can. Biking or walking 10 miles each day instead of riding in a car can save up to 1.9 tons of carbon dioxide from entering the atmosphere every year.

Reduce and reuse things as much as possible. Factories emit lots of carbon dioxide when making new products. (Buying products that are made with recycled glass and plastic also emits carbon dioxide, though less so.) Fix your appliances and clothes instead of buying new products. Good thing holey jeans are back in style!

Wash your clothes in cold water, and hang them to dry.

Electronics use energy even when they're turned off, so unplug them when you're not using them. It could save your family about $200 a year on its energy bill.

Eat less meat and dairy. Farm animals, er, emit another heat-trapping gas, methane. And some studies have found that livestock account for about half of the world's heat-trapping gas emissions.

Buy locally grown and in-season foods and products to reduce emissions from transporting products.

Wear a warm sweater at home in the winter instead of turning up the heat, and open your windows instead of blasting the air conditioning in the summer.

Talk to your parents and the other adults that you know about climate change. Send a letter or drawing to your mayor, Senate or House representative, or even to the president. These leaders can vote to regulate and reduce carbon dioxide emissions.

Your everyday actions affect people, plants, and animals all over the world-including polar bears! So be cool by doing your best to keep Earth well ... cool!

Climate: The average pattern of weather conditions over a long period of time. Climate isn't weather-weather changes daily.

Global warming: The increate in Earth's average temperature over a long period of time

Carbon dioxide: A gas released by the burning of coal, natural gas, oil, and wood that traps heat in the atmosphere

Carbon footprint: The amount of carbon dioxide one human releases into the environment in a year

Fossil fuels: Coal, oil, and natural gas, which come from the breakdown of ancient plants and animals over millions of years

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What is climate change? What could happen? Get all the facts you need to know.

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6 Easy Ways to Fight Climate Change Every Day

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This explainer was updated by Umair Irfan in December 2018 and draws heavily from a written by Brad Plumer in 2015. Brian Resnick contributed the section on the Paris climate accord in 2017.
There's a vast and growing gap between the urgency to fight climate change and the policies needed to combat it.

In 2018, the United Nations' Intergovernmental Panel on Climate Change found that it is possible to limit global warming to 1.5 degrees Celsius this century, but the world may have as little as 12 years left to act. The US government's National Climate Assessment, with input from NASA, the Environmental Protection Agency, and the Pentagon, also reported that the consequences of climate change are already here, ranging from nuisance flooding to the spread of mosquito-borne viruses into what were once colder climates. Left unchecked, warming will cost the US economy hundreds of billions of dollars.

However, these facts have failed to register with the Trump administration, which is actively pushing policies that will increase the emissions of heat-trapping gases.

Ever since he took office, President Donald Trump has rejected or undermined President Barack Obama's signature climate achievements: the Paris climate agreement; the Clean Power Plan, the main domestic policy for limiting greenhouse gas emissions; and fuel economy standards, which target transportation, the largest US source of greenhouse gases.

Trump has also appointed climate change skeptics to key positions. Quietly, officials at these and other science agencies have been removing the words "climate change" from government websites and press releases.

The big questions now are how these ongoing changes in the climate will reverberate throughout the rest of the world, and what we should do about them. The answers bridge decades of research across geology, economics, and social science, which have been confounded by uncertainty and obscured by jargon. That's why it can be a bit daunting to join the discussion for the first time, or to revisit the conversation after a hiatus.

To help, we've provided answers to some fundamental questions about climate change you may have been afraid to ask.

1) What is global warming?

In short: The world is getting hotter, and humans are responsible.

Yes, the planet's temperature has changed before, but it's the rise in average temperature of the Earth's climate system since the late 19th century, the dawn of the Industrial Revolution, that's important here. Temperatures over land and ocean have gone up 0.8° to 1° Celsius (1.4° to 1.8° Fahrenheit), on average, in that span:

Many people use the term "climate change" to describe this rise in temperatures and the associated effects on the Earth's climate.(The shift from the term "global warming" to "climate change" was also part of a deliberate messaging effort by a Republican pollster to undermine support for environmental regulations.)

Global warming also refers to what scientists think will happen in the future if humans keep adding greenhouse gases to the atmosphere.

Many experts consider 2°C of warming to be unacceptably high, increasing the risk of deadly heat waves, droughts, flooding, and extinctions. Rising temperatures will drive up global sea levels as the world's glaciers and ice sheets melt. Further global warming could affect everything from our ability to grow food to the spread of disease.

That's why the IPCC put out another report in 2018 comparing 2°C of warming to a scenario with 1.5°C of warming. The researchers found that this half-degree difference is actually pretty important, since every bit of warming matters. Between the two outlooks, less warming means fewer people will have to move from coastal areas, natural weather events will be less severe, and economies will take a smaller hit.

However, limiting warming would likely require a complete overhaul of our energy system. Fossil fuels currently provide just over 80 percent of the world's energy. To zero out emissions this century, we'd have to replace most of that with low-carbon sources like wind, solar, nuclear, geothermal, or carbon capture.

Beyond that, we may have to electrify everything that uses energy and start pulling greenhouse gases straight from the air. And to get on track for 1.5°C of warming, the world would have to halve greenhouse gas emissions from current levels by 2030.

That's a staggering task, and there are huge technological and political hurdles standing in the way. As such, the world's nations have been slow to act on global warming - many of the existing targets for curbing greenhouse gas emissions are too weak, yet many countries are falling short of even these modest goals.

2) How do we know global warming is real?

But that's not the only clue. Scientists have also noted that glaciers and ice sheets around the world are melting. Satellite observations since the 1970s have shown warming in the lower atmosphere. There's more heat in the ocean, causing water to expand and sea levels to rise. Plants are flowering earlier in many parts of the world. There's more humidity in the atmosphere. Here's a summary from the National Oceanic and Atmospheric Administration:

These are all signs that the Earth really is getting warmer - and that it's not just a glitch in the thermometers. That explains why climate scientists say things like, "Warming in the climate system is unequivocal." They're really confident about this one.

3) How do we know humans are causing global warming?

Climate scientists say they are more than 95 percent certainthat human influence has been the dominant cause of global warming since 1950. They're about as sure of this as they are that cigarette smoke causes cancer.

Why are they so confident? In part because they have a good grasp of how greenhouse gases can warm the planet, in part because the theory fits the available evidence, and in part because alternate theories have been ruled out. Let's break it down in six steps:

1) Scientists have long known that greenhouse gases in the atmosphere - such as carbon dioxide, methane, or water vapor - absorb certain frequencies of infrared radiation and scatter them back toward the Earth. These gases essentially prevent heat from escaping too quickly back into space, trapping that radiation at the surface and keeping the planet warm.

2) Climate scientists also know that concentrations of greenhouse gases in the atmosphere have grown significantly since the Industrial Revolution. Carbon dioxide has risen 45 percent. Methane has risen more than 200 percent. Through some relatively straightforward chemistry and physics, scientists can trace these increases to human activities like burning oil, gas, and coal.

3) So it stands to reason that more greenhouse gases would lead to more heat. And indeed, satellite measurements have shown that less infrared radiation is escaping out into space over time and instead returning to the Earth's surface. That's strong evidence that the greenhouse effect is increasing.

4) There are other human fingerprints that suggest increased greenhouse gases are warming the planet. For instance, back in the 1960s, simple climate models predicted that global warming caused by more carbon dioxide would lead to cooling in the upper atmosphere (because the heat is getting trapped at the surface). Later satellite measurements confirmed exactly that. Here are a few other similar predictions that have also been confirmed.

5) Meanwhile, climate scientists have ruled out other explanations for the rise in average temperatures over the past century. To take one example: Solar activity can shift from year to year, affecting the Earth's climate. But satellite data shows that total solar irradiance has declined slightly in the past 35 years, even as the Earth has warmed.

6) More recent calculations have shown that it's impossible to explain the temperature rise we've seen in the past century without taking the increase in carbon dioxide and other greenhouse gases into account. Natural causes, like the sun or volcanoes, have an influence, but they're not sufficient by themselves.

Ultimately, the Intergovernmental Panel on Climate Change concluded that most of the warming since 1951 has been due to human activities. The Earth's climate can certainly fluctuate from year to year due to natural forces (including oscillations in the Pacific Ocean, such as El Niño). But greenhouse gases are driving the larger upward trend in temperatures.

And as the Climate Science Special Report, released by 13 US federal agencies in November 2017, put it, "For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence."

More: This chart breaks down all the different factors affecting the Earth's average temperature. And there's much more detail in the IPCC's report, particularly this section and this one.

4) How has global warming affected the world so far?

Here's a list of ongoing changes that climate scientists have concluded are likely linked to global warming, as detailed by the IPCC here and here.

Higher temperatures: Every continent has warmed substantially since the 1950s. There are more hot days and fewer cold days, on average, and the hot days are hotter.

Heavier storms and floods: The world's atmosphere can hold more moisture as it warms. As a result, the overall number of heavier storms has increased since the mid-20th century, particularly in North America and Europe (though there's plenty of regional variation). Scientists reported in December that at least 18 percent of Hurricane Harvey's record-setting rainfall over Houston in August was due to climate change.

Heat waves: Heat waves have become longer and more frequent around the world over the past 50 years, particularly in Europe, Asia, and Australia.

Shrinking sea ice: The extent of sea ice in the Arctic, always at its maximum in winter, has shrunk since 1979, by 3.3 percent per decade. Summer sea ice has dwindled even more rapidly, by 13.2 percent per decade. Antarctica has seen recent years with record growth in sea ice, but it's a very different environment than the Arctic, and the losses in the north far exceed any gains at the South Pole, so total global sea ice is on the decline:

Shrinking glaciers and ice sheets: Glaciers around the world have, on average, been losing ice since the 1970s. In some areas, that is reducing the amount of available freshwater. The ice sheet on Greenland, which would raise global sea levels by 25 feet if it all melted, is declining, with some sections experiencing a sudden surge in the melt rate. The Antarctic ice sheet is also getting smaller, but at a much slower rate.

Sea level rise: Global sea levels rose 9.8 inches (25 centimeters) in the 19th and 20th centuries, after 2,000 years of relatively little change, and the pace is speeding up. Sea level rise is caused by both the thermal expansion of the oceans - as water warms up, it expands - and the melting of glaciers and ice sheets (but not sea ice).

Food supply: A hotter climate can be both good for crops (it lengthens the growing season, and more carbon dioxide can increase photosynthesis) and bad for crops (excess heat can damage plants). The IPCC found that global warming was currently benefiting crops in some high-latitude areas but that negative effects are becoming increasingly common worldwide. In areas like California, crop yields are estimated to decline 40 percent by 2050.

Shifting species: Many land and marine species have had to shift their geographic ranges in response to warmer temperatures. So far, several extinctions have been linked to global warming, such as certain frog species in Central America.

Warmer winters: In general, winters are warming faster than summers. Average low temperatures are rising all over the world. In some cases, these temperatures are climbing above the freezing point of water. We're already seeing massive declines in snow accumulation in the United States, which can paradoxically increase flood, drought, and wildfire risk - as water that would ordinarily dispatch slowly over the course of a season instead flows through a region all at once.

Debated impacts

Here are a few other ways the Earth's climate has been changing - but scientists are still debating whether and how they're linked to global warming:

Droughts have become more frequent and more intense in some parts of the world - such as the American Southwest, Mediterranean Europe, and West Africa - though it's hard to identify a clear global trend. In other parts of the world, such as the Midwestern United States and Northwestern Australia, droughts appear to have become less frequent. A recent study shows that, globally, the time between droughts is shrinking and more areas are affected by drought and taking longer to recover from them.

5) What impacts will global warming have in the future?

It depends on how much the planet actually heats up. The changes associated with 4° Celsius (or 7.2° Fahrenheit) of warming are expected to be more dramatic than the changes associated with 2°C of warming.

Here's a basic rundown of big impacts we can expect if global warming continues, via the IPCC (here and here).

Hotter temperatures: If emissions keep rising unchecked, then global average surface temperatures will be at least 2°C higher (3.6°F) than preindustrial levels by 2100 - and possibly 3°C or 4°C or more.

Higher sea level rise: The expert consensus is that global sea levels will rise somewhere between 0.2 and 2 meters by the end of the century if global warming continues unchecked (that's between 0.6 and 6.6 feet). That's a wide range, reflecting some of the uncertainties scientists have in how ice will melt. In specific regions like the Eastern United States, sea level rise could be even higher, and around the world, the rate of rise is accelerating.

Heat waves: A hotter planet will mean more frequent and severe heat waves.

Droughts and floods: Across the globe, wet seasons are expected to become wetter, and dry seasons drier. As the IPCC puts it, the world will see "more intense downpours, leading to more floods, yet longer dry periods between rain events, leading to more drought."

Hurricanes: It's not yet clear what impact global warming will have on tropical cyclones. The IPCC said it was likely that tropical cyclones would get stronger as the oceans heat up, with faster winds and heavier rainfall. But the overall number of hurricanes in many regions was likely to "either decrease or remain essentially unchanged."

Heavier storm surges: Higher sea levels will increase the risk of storm surges and flooding when storms do hit.

Agriculture: In many parts of the world, the mix of increased heat and drought is expected to make food production more difficult. The IPCC concluded that global warming of 1°C or more could start hurting crop yields for wheat, corn, and rice by the 2030s, especially in the tropics. (This wouldn't be uniform, however; some crops may benefit from mild warming, such as winter wheat in the United States.)

Extinctions: As the world warms, many plant and animal species will need to shift habitats at a rapid rate to maintain their current conditions. Some species will be able to keep up; others likely won't. The Great Barrier Reef, for instance, may not be able to recover from major recent bleaching events linked to climate change. The National Research Council has estimated that a mass extinction event "could conceivably occur before the year 2100."

Long-term changes: Most of the projected changes above will occur in the 21st century. But temperatures will keep rising after that if greenhouse gas levels aren't stabilized. That increases the risk of more drastic longer-term shifts. One example: If West Antarctica's ice sheet started crumbling, that could push sea levels up significantly. The National Research Council in 2013 deemed many of these rapid climate surprises unlikely this century but a real possibility further into the future.

6) What happens if the world heats up more drastically - say, 4°C?

The risks of climate change would rise considerably if temperatures rose 4° Celsius (7.2° Fahrenheit) above preindustrial levels - something that's possible if greenhouse gas emissions keep rising at their current rate.

The IPCC says 4°C of global warming could lead to "substantial species extinctions," "large risks to global and regional food security," and the risk of irreversibly destabilizing Greenland's massive ice sheet.

One huge concern is food production: A growing number of studiessuggest it would become significantly more difficult for the world to grow food with 3°C or 4°C of global warming. Countries like Bangladesh, Egypt, Vietnam, and parts of Africa could see large tracts of farmland turn unusable due to rising seas. Scientists are also concerned about crops getting less nutritious due to rising CO2.

Humans could struggle to adapt to these conditions. Many people might think the impacts of 4°C of warming will simply be twice as bad as those of 2°C. But as a 2013 World Bank report argued, that's not necessarily true. Impacts may interact with each other in unpredictable ways. Current agriculture models, for instance, don't have a good sense of what will happen to crops if increased heat waves, droughts, new pests and diseases, and other changes all start to combine.

"Given that uncertainty remains about the full nature and scale of impacts," the World Bank report said, "there is also no certainty that adaptation to a 4°C world is possible." Its conclusion was blunt: "The projected 4°C warming simply must not be allowed to occur."

That depends on your faith in humanity.

Climate models depend on not only complicated physics but the intricacies of human behavior over the entire planet.

Generally, the more greenhouse gases humanity pumps into the atmosphere, the warmer it will get. But scientists aren't certain how sensitive the global climate system is to increases in greenhouse gases. And just how much we might emit over the coming decades remains an open question, depending on advances in technology and international efforts to cut emissions.

The IPCC groups these scenarios into four categories of atmospheric greenhouse gas concentrations known as Representative Concentration Pathways. They serve as standard benchmarks for evaluating climate models, but they also have some assumptions baked in.

RCP 2.6, also called RCP 3PD, is the scenario with very low greenhouse gas concentrations in the atmosphere. It bets on declining oil use, a population of 9 billion by 2100, increasing energy efficiency, and emissions holding steady until 2020, at which point they'll decline and even go negative by 2100. This is, to put it mildly, very optimistic.

The next tier up is RCP 4.5, which still banks on ambitious reductions in emissions but anticipates an inflection point in the emissions rate around 2040. RCP 6 expects emissions to increase 75 percent above today's levels before peaking and declining around 2060 as the world continues to rely heavily on fossil fuels.

The highest tier, RCP 8.5, is the pessimistic business-as-usual scenario, anticipating no policy changes nor any technological advances. It expects a global population of 12 billion and triple the rate of carbon dioxide emissions compared to today by 2100.

Here's how greenhouse gas emissions under each scenario stack up next to each other:

And here's what that means for global average temperatures, assuming that a doubling of carbon dioxide concentrations in the atmosphere leads to 3°C of warming:

As you can see, RCP 3PD is the only trajectory that keeps the planet below 2°C of warming. Recall what it would take to keep emissions in line with this pathway and you'll understand the enormity of the challenge of meeting this goal.

8) How do we stop global warming?

The world's nations would need to cut their greenhouse gas emissions by a lot. And even that wouldn't stop all global warming.

For example, let's say we wanted to limit global warming to below 2°C. To do that, the IPCC has calculated that annual greenhouse gas emissions would need to drop at least 40 to 70 percent by midcentury.

Emissions would then have to keep falling until humans were hardly emitting any extra greenhouse gases by the end of the century. We'd also have to remove carbon dioxide from the atmosphere.

Cutting emissions that sharply is a daunting task. Right now, the world gets 87 percent of its primary energy from fossil fuels: oil, gas, and coal. By contrast, just 13 percent of the world's primary energy is "low carbon": a little bit of wind and solar power, some nuclear power plants, a bunch of hydroelectric dams. That's one reason global emissions keep rising each year.

To stay below 2°C, that would all need to change radically. By 2050, the IPCC notes, the world would need to triple or even quadruple the share of clean energy it uses - and keep scaling it up thereafter. Second, we'd have to get dramatically more efficient at using energy in our homes, buildings, and cars. And stop cutting down forests. And reduce emissions from agriculture and from industrial processes like cement manufacturing.

The IPCC also notes that this task becomes even more difficult the longer we put it off, because carbon dioxide and other greenhouse gases will keep piling up in the atmosphere in the meantime, and the cuts necessary to stay below the 2°C limit become more severe.

9) What are we actually doing to fight climate change?

A global problem requires global action, but with climate change, there is a yawning gap between ambition and action.

The main international effort is the 2015 Paris climate accord, of which the United States is the only country in the world that wants out. The deal was hammered out over weeks of tense negotiations and weighs in at 31 pages. What it does is actually pretty simple.

The backbone is the global target of keeping global average temperatures from rising 2°C (compared to temperatures before the Industrial Revolution) by the end of the century. Beyond 2 degrees, we risk dramatically higher seas, changes in weather patterns, food and water crises, and an overall more hostile world.
Paris is voluntary
Critics have argued that the 2-degree mark is arbitrary, or even too low, to make a difference. But it's a starting point, a goal that, before Paris, the world was on track to wildly miss.

To accomplish this 2-degree goal, the accord states that countries should strive to reach peak emissions "as soon as possible." (Currently, we're on track to hit peak emissions around 2030 or later, which will likely be too late.)

But the agreement doesn't detail exactly how these countries should do that. Instead, it provides a framework for getting momentum going on greenhouse gas reduction, with some oversight and accountability. For the US, the pledge involves 26 to 28 percent reductions by 2025. (Under Trump's current policies, that goal is impossible.)

There's also no defined punishment for breaking it. The idea is to create a culture of accountability (and maybe some peer pressure) to get countries to step up their climate game.

In 2020, delegates are supposed to reconvene and provide updates about their emission pledges and report on how they're becoming more aggressive on accomplishing the 2-degree goal.
Paris asks richer countries to help out poorer countries
However, many countries are already falling behind on their climate change commitments, and some, like Germany, are giving up on their near-term targets.

There's a fundamental inequality when it comes to global emissions. Rich countries have plundered and burned huge amounts of fossil fuels and gotten rich from them. Poor countries seeking to grow their economies are now being admonished for using the same fuels. Many low-lying poor countries also will be among the first to bear the worst impacts of climate change.
The agreement matters because we absolutely need momentum on this issue
The main vehicle for rectifying this is the Green Climate Fund, via which richer countries, like the US, are supposed to send $100 billion a year in aid and financing by 2020 to the poorer countries. The United States' share was $3 billion, but with President Trump's decision to withdraw from the Paris accord, this goal is unlikely to be met.

The Paris agreement is largely symbolic, and it will live oneven though Trump is aiming to pull the US out. But, as Jim Tankersley wrote for Vox, "the accord will be weakened, and, much more importantly, so will the fragile international coalition" around climate change.
But the Paris accord isn't the only international climate policy game in town
We're already seeing the Paris agreement lose steam. At a follow-up climate meeting this year in Katowice, Poland, negotiators forged an agreement on measuring and verifying their progress in cutting greenhouse gases, but left many critical questions of how to achieve these reductions unanswered.

There are regional international climate efforts like the European Union's Emissions Trading System. However, the most effective global policy at keeping warming in check to date doesn't have to do with climate change, at least on the surface.
Avoiding catastrophic climate change isn't impossible yet. Just incredibly hard. Reckoning with climate change will demand ugly tradeoffs from environmentalists - and everyone else Show this cartoon to anyone who doubts we need huge action on climate change It's time to start talking about "negative" carbon dioxide emissions
The 1987 Montreal Protocol, which was convened by countries to halt the destruction of the ozone layer, had a major side effect of averting warming. In fact, it's been the single most effective effort humanity has undertaken to fight climate change. Since many of the substances that eat away at the ozone layer are potent heat-trappers, limiting emissions of gases like chlorofluorocarbons has an outsize effect.
Scientists made a detailed "roadmap" for meeting the Paris climate goals. It's eye-opening.
And the Trump administration doesn't appear as hostile to Montreal as it does to Paris. The White House may send the 2016 Kigali Amendment to the Montreal Protocol to the Senate for ratification, giving the new regulations the force of law. If implemented, the amendment would avert 0.5°C of warming by 2100.

Regardless of what path we choose, the key thing to remember is that we are going to pay for climate change one way or another. We have the opportunity now to address warming on our own terms, with investments in clean energy, moving people away from disaster-prone areas, and regulating greenhouse gas emissions. Otherwise, we'll pay through diminished crop harvests, inundated coastlines, destroyed homes, lost lives, and an increasingly unlivable planet. Ignoring or stalling on climate change chooses the latter option by default. Our choices do matter, but we're running out of time to make them.

A history of the 2°C global warming target

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9 questions about climate change you were too embarrassed to ask

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Basic answers to basic questions about global warming and the future climate.

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National Snow and Ice Data Center, W. O. Field, B. F. Molnia.

Can you feel the world getting warmer? Maybe you can't, but ice across the planet's surface has certainly been feeling the heat, according to new reports. Indeed, the dramatic shrinkage of Arctic ice-and at some spots, its seasonal near disappearance-is one sure sign that our planet has developed a fever.

So are glaciers-and not only at the poles. Around the world these massive moving fields of ice have been posting record losses. The World Glacier Monitoring Service, based at the University of Zurich in Switzerland, looked at nearly 30 reference glaciers in nine different mountain ranges across the globe. In March, its scientists reported disturbing news. The average melting and thinning rate of those glaciers has more than doubled between the 2004 and 2006.

"The latest figures are part of what appears to be an accelerating trend with no apparent end in sight," said Wilfried Haeberli, who directs the glacier-monitoring group.

In Antarctica, a large chunk of the Wilkins Ice Shelf recently collapsed into the sea. Satellite images show the Wilkins Shelf began falling apart in late February, when a large iceberg 41 kilometers by 2.5 kilometers (25.5 miles by 1.5 miles) broke away from the shelf. This triggered a runaway disintegration of an additional 405 square kilometers (160 square miles) of the shelf. The total loss was 8.5 times the area covered by New York's Manhattan island. As of March 23, only a 6 km (3.7 mile) wide strip of intact ice was protecting the shelf from further collapse.

Scientists from the U.S. National Snow and Ice Data Center and the British Antarctic Survey put the blame for the Wilkins' massive melt-triggered event on a warmer world. "We believe the Wilkins [Shelf] has been in place for at least a few hundred years," said Ted Scambos, a lead scientist with the snow and ice data center. "But warm air and exposure to ocean waves are causing a break-up."

With strong evidence that ice is melting globally atop mountains and at Earth's poles, scientists say that it's pretty clear our planet is warming. And that could spell big changes even in regions where the only ice you'd normally encounter is in a beverage.

National Snow and Ice Data Center, Boulder, CO

Arctic ice on the rocks
Changes in the Arctic's sea ice offer more cause for concern. That's the March 18 conclusion of a team of federal scientists who performed a recent checkup on this cold region.

The Arctic is a normally ice-covered ocean surrounded by land. Sea ice grows and shrinks seasonally-building throughout the cold, sunless winter and then melting somewhat during the sunny, warmer summer.

Satellite data has shown that a colder-than-average winter this year has actually increased the amount of the Arctic's new-or seasonal-ice. However, some ice in this region can last for up to 10 years. This older-or perennial- sea ice has continued to decline.

"Perennial ice can be very thick and very tough, but there's much less of it left," says Walt Meier of the National Snow and Ice Data Center. "There's much more seasonal ice, which is weaker and thinner." It's also especially vulnerable to the summer sun.

The Arctic remains dark for all or part of each day throughout much of the winter. When the sun returns in the spring and a warming begins, the seasonal ice "is going to melt away," Meier warns. So any winter gains in ice cover "are going to be quickly lost."

National Snow and Ice Data Center, Boulder, CO

Perennial ice used to cover 50 to 60 percent of the Arctic, according to data collected by the National Aeronautics and Space Administration. This year it covers less than 30 percent. "Since the mid 1980s, we've lost about a million square miles of perennial ice," says Meier. "That's about one and half times [the size of] the state of Alaska."

The very old, tough ice that's been around for six years or more also has declined. Once making up more than 20 percent of the Arctic area in the mid- to late 1980s, it now covers just six percent of the region.

Meier says that this is a record low for perennial ice in winter and a very sharp drop even from last winter. "There's this fear," he says, "that we're going over a cliff, in a sense, with this perennial ice." He says the planet could be heading towards a situation where there won't be any perennial ice left in the near future. Only seasonal ice would exist, which means that the Arctic Ocean would be ice-free during the summer.

The decline of Arctic sea ice "is an iconic signal of global warming," Meier says. It's something that really sticks out "as being clear cut and definitely due to global warming."
Real warming, real warning

National Snow and Ice Data Center, courtesy S. Drobot, Univ. of Colorado, Boulder

Most scientists believe people are largely responsible for the warming of Earth's atmosphere throughout the past century. Their burning of fossil fuels-such as coal, oil, and gas-releases greenhouse gases that trap the sun's heat.

Until fairly recently, scientists debated whether Earth's fever was likely to last only a few years or whether it could persist for decades-maybe even longer.

Now the debate appears to be over.

There is a scientific consensus, which means an agreement among the vast majority of researchers in the field, that global warming is not a temporary blip. The pattern of worldwide warming appears to signal a true and potentially very long-term change in climate. Indeed, global warming is "unequivocal," the Intergovernmental Panel on Climate Change (IPCC) stated last year in a convincing set of reports.

Susan Solomon is a senior scientist at the National Oceanic and Atmospheric Administration in Boulder, Colo., who led one of the IPCC working groups. Using the word "unequivocal" was important, she says. The data that the IPCC reviewed were so strong, she explains, that the words "very likely" just wouldn't get the point across. There's a greater than 99 percent chance that our planet has warmed, she says. So there really "just isn't any doubt about it."

The IPCC reports describe possible dramatic and lasting impacts of global warming that may occur. But, cautions Solomon, the warming and impacts that we'll see in the next century depend a lot on how much carbon dioxide we emit. Carbon dioxide, a pollutant emitted as fossil fuels burn, is a major greenhouse gas.

How severely the climate changes and precisely when and where those changes occur remain uncertain. If humanity drastically reduced its emissions of greenhouse gases, such as carbon-dioxide emissions, we could reduce how high Earth's surface temperatures climb, Solomon says. But if we don't, she warns, by the end of the century Earth's average temperature could climb somewhere between 2 and 6 degrees Celsius (3.6 to 10.8 degrees Fahrenheit).

"And under those circumstances, a lot of things would change," Solomon says. "We'd see more drought, more heat waves. We'd also, ironically, see more heavy rainfall. We'd see sea levels rise-and though there's a lot of uncertainty in how much they'd rise, numbers like half a meter [about 20 inches] wouldn't surprise me in 100 years."

Such projections about droughts and sea-level rise aren't certain. They are simply "best guesses," Meier observes. "They could be wrong," he says. In fact, he notes, "Many skeptics focus on the fact that things might not be quite as bad as projected." On the other hand, he points out that the effects of Earth's fever could prove much worse than scientists have anticipated, "which is what we're already seeing in terms of the rate of ice melt."
No summer sea ice-soon?
The Arctic has shown the most rapid rates of warming in recent years. Surface air temperatures there have warmed at roughly twice the global rate, according to the IPCC reports. Science has predicted that the first signs of global warming would show up first and most dramatically in the Arctic. "And that's indeed what we're seeing with the decline of Arctic sea ice," says Meier.

The IPCC reports have concluded that the Arctic Ocean could lose its summer sea ice by the latter part of the century. Meier cautions, however, that such estimates are based on computer models. Those models are not up to date. In fact, he says, we're finding that changes are occurring "much, much faster than the models have projected. The way things are going it's likely that we'll have an ice-free Arctic Ocean in the summer within a couple of decades. It could be even sooner." Indeed, some scientists have speculated summer sea ice could disappear by 2013-only five years from now. "That's on the extreme pessimistic edge of the estimates," Meier says, "but it's not implausible any longer."

He thinks the complete disappearance of summer sea ice in the Arctic is probably unavoidable. The warming trend is just too strong and seems to be accelerating.

"You don't need just one cold summer or one cold winter to turn things around," he explains. "It would take many, many cold years in a row to reverse things and get things back to the way they were in the 1980s. And that's not very likely." That's especially true, he says, because people are still using fossil fuels-and spewing greenhouse gases-at high and growing rates.

Though it may be too late to save the Arctic Ocean from experiencing ice-free summers, "it's not too late to prevent the worst of the impacts of global warming," Meier argues. "The sea ice is an early warning and we can heed that warning. There is hope and there are solutions."

Next week: Part 2: What's behind global warming, and what can we do?

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Glaciers have retreated dramatically all over world. Here are some photos of Alaska's Muir Glacier, photographed by glaciologist William O. Field on 13 August 1941 (left) and by geologist Bruce F. Molnia on 31 August 2004 (right). National Snow and Ice Data Center, W. O. Field, B. F. Molnia.

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Climate Change: Vital Signs of the Planet

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The Greenhouse Effect

Increasing Greenhouses Gases Are Warming the Planet

Scientists attribute the global warming trend observed since the mid-20 th century to the human expansion of the "greenhouse effect" ¹ - warming that results when the atmosphere traps heat radiating from Earth toward space.

Life on Earth depends on energy coming from the Sun. About half the light energy reaching Earth's atmosphere passes through the air and clouds to the surface, where it is absorbed and radiated in the form of infrared heat. About 90% of this heat is then absorbed by greenhouse gases and re-radiated, slowing heat loss to space.

Gases that Contribute

The Role of Humans

Human Activity Is the Cause of Increased Greenhouse Gas Concentrations

Over the last century, burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO ₂). This increase happens because the coal or oil burning process combines carbon with oxygen in the air to make CO ₂. To a lesser extent, clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.

How do we know what greenhouse gas and temperature levels were in the distant past?

Ice cores are scientists' best source for historical climate data. Other tools for learning about Earth's ancient atmosphere include growth rings in trees, which keep a rough record of each growing season's temperature, moisture and cloudiness going back about 2,000 years. Corals also form growth rings that provide information about temperature and nutrients in the tropical ocean. Other proxies, such as benthic cores, extend our knowledge of past climate back about a billion years.

detailed answer

The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels by nearly 50% since 1750 ². This increase is due to human activities, because scientists can see a distinctive isotopic fingerprint in the atmosphere.

In its Sixth Assessment Report, the Intergovernmental Panel on Climate Change, composed of scientific experts from countries all over the world, concluded thatit is unequivocal that the increase of CO ₂, methane, and nitrous oxide in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere and biosphere.

"Since systematic scientific assessments began in the 1970s, the influence of human activity on the warming of the climate system has evolved from theory to established fact."

- Intergovernmental Panel on Climate Change

The panel's AR6 Working Group I (WGI) Summary for Policymakers report is online at https://www.ipcc.ch/report/ar6/wg1/.

Is the Sun to Blame?

Evidence Shows That Current Global Warming Cannot Be Explained by Solar Irradiance

Scientists use a metric called Total Solar Irradiance (TSI) to measure the changes in energy the Earth receives from the Sun. TSI incorporates the 11-year solar cycle and solar flares/storms from the Sun's surface.

Studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity coupled with increased volcanic activity helped trigger the Little Ice Age.

The above graph compares global surface temperature changes (red line) and the Sun's energy that Earth receives (yellow line) in watts (units of energy) per square meter since 1880. The lighter/thinner lines show the yearly levels while the heavier/thicker lines show the 11-year average trends. Eleven-year averages are used to reduce the year-to-year natural noise in the data, making the underlying trends more obvious.

The amount of solar energy that Earth receives has followed the Sun's natural 11-year cycle of small ups and downs with no net increase since 1880. Over the same period, global temperature has risen markedly. It is therefore extremely unlikely that the Sun has caused the observed global temperature warming trend over the past half-century. Credit: NASA/JPL-Caltech

But several lines of evidence show that current global warming cannot be explained by changes in energy from the Sun:

Since 1750, the average amount of energy from the Sun either remained constant or decreased slightly³.

If a more active Sun caused the warming, scientists would expect warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere and a warming at the surface and lower parts of the atmosphere. That's because greenhouse gases are slowing heat loss from the lower atmosphere.

Climate models that include solar irradiance changes can't reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.
References
References

1. IPCC 6 th Assessment Report, WG1, Summary for Policy Makers, Sections A, " The Current State of the Climate "

IPCC 6 th Assessment Report, WG1, Technical Summary, Sections TS.1.2, TS.2.1 and TS.3.1

2. P. Friedlingstein, et al., 2022: "Global Carbon Budget 2022", Earth System Science Data ( 11 Nov 2022): 4811-4900. https://doi.org/10.5194/essd-14-4811-2022

3. IPCC 6 th Assessment Report, WG1, Chapter 2, Section 2.2.1, " Solar and Orbital Forcing"

IPCC 6 th Assessment Report, WG1, Chapter 7, Sections 7.3.4.4, 7.3.5.2, Figure 7.6, " Solar"

M. Lockwood and W.T. Ball, Placing limits on long-term variations in quiet-Sun irradiance and their contribution to total solar irradiance and solar radiative forcing of climate," Proceedings of the Royal Society A, 476, issue 2228 (24 June 2020): https://doi 10.1098/rspa.2020.0077

Header image credit: Pixabay/stevepb

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Vital Signs of the Planet: Global Climate Change and Global Warming. What is the "greenhouse effect"? What is causing it? Are humans to blame? What does solar irradiance have to do with it? Answers here.

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Climate Change 101 with Bill Nye | National Geographic

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The Science of Climate Change in National Parks Video Series - Climate Change (U.S. National Park Service)

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The discussion surrounding climate change is often focused on natural resources. The National Park Service is also tasked with preserving and protecting cultural and historical resources, and they are relevant to climate change too. In this video, National Park Service staff and partnering scientists talk about climate change in the context of Jamestown Island in Virginia, the site of the first permanent English settlement.

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As of Monday, October 24, content that was on TweenTribune.com will now be available here on our new educational resources page and on our learning pages. While much of the content that you enjoyed will still exist, educators will unfortunately no longer be able to assign content to students. Tween Tribune has been a valued educational brand of Smithsonian magazine, and we appreciate your continued support.

Though the Girl Scouts of the USA initially declared itself a space for all girls, the reality was different for girls of color

Erin Blakemore

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As of Monday, October 24, content that was on TweenTribune.com will now be available here on our new educational resources page and on our learning pages. While much of the content that you enjoyed will still exist, educators will unfortunately no longer be able to assign content to students.

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The Science of Climate Change Explained: Facts, Evidence and Proof

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Definitive answers to the big questions.

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Traditional practices have also undergone the impact of climate change. Before her grandfather died, Jennifer interviewed him about his favorite spot for hunting seals, which was only reachable when the water was frozen solid. "It doesn't get that cold anymore, so it doesn't actually freeze anymore," Jennifer says. "The traditional knowledge that has been passed down orally, telling stories of that particular place, it was gone with him. He was the last of his family to have known all the traditional knowledge of that specific place."

A week before we were in Cape Dorset, ice barricaded the Inuit community. Ships normally can get through the Arctic for only about six weeks in the summer. The only way out most of the year is by snowmobile or airplane, according to what locals told me.

In July, the roads are ditches of mud. Clouds of mosquitoes swarmed Brianna Rowe, 26, a shipmate I followed as she interviewed Inuit children and teachers about their lives, school, family, and traditions.

Brianna, who works for Reach the World and is director of the climate-change education project Disappearing Ice, connects classrooms with travelers via the Internet, so kids can travel the world virtually. She was using her vacation, as a student member of the Explorers Club, to connect U.S. classrooms with Arctic classrooms so kids can learn about one another's cultures - including how the U.S. is one of the main countries affecting the climate much farther north.

"The decisions that people make in the U.S. have a global impact," Brianna tells Teen Vogue. "It is important for everybody to be aware of their decisions, and their impact on the environment has an effect on the entire world's environment."

Kristin Gates, a park ranger who trekked alone across the Brooks Range, knows this all too well. Part of the year, 30-year-old Kristin patrols Denali National Park by dog sled, and she's making a short film about plastics pollution and garbage in the Arctic. "Climate change is something that affects us every day during the winter months," she tells Teen Vogue. Frozen rivers are Alaska's highways, and when they don't freeze solid, travel becomes dangerous and difficult.

Unfortunately, mushing (a form of travel that relies on dogs to pull a sled), which Kristin was hoping to learn about first-hand, is now almost nonexistent. Dog mushing as a practice mostly died out after Inuit communities were settled in villages by the Canadian government in the 1950s, so she heard stories about the old days but has not found anyone traveling by dog sled. Nowadays, travel mostly uses motors and gas, in four-wheelers, snowmobiles, and trucks. Kristin enlisted some of us from the ship and others from the community to clean up the beach. In about an hour we collected 17 bags of trash, a potential threat to seabirds and mammals.

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I Went to the Canadian Arctic and Saw Climate Change's Impact First-Hand

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In this reported piece, 12-year-old writer Roxanna Pearl Beebe-Center explains what she learned about the impact of climate change on animals while visiting the Canadian Arctic.

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A breakthrough deal to attempt to limit global temperature rises was agreed at a conference of world nations in December 2015. These charts from the time show how and why the Earth's climate is changing.

1. What is the problem?

The world is getting warmer

The average temperature of the Earth's surface has increased by about 0.85°C (1.4F) in the last 100 years. Up until 2015, 13 of the 14 warmest years had been recorded in the 21st Century. 2015 then became the hottest year on record, but was surpassed by record-breaking 2016.

10 warmest years

10 coldest years

20th Century average temperature

Hotter

Colder

Source: NOAA

2. Why is this happening?

Greenhouse gases, mainly carbon dioxide

Scientists believe that gases released from industry and agriculture (known as emissions) are adding to the natural greenhouse effect, the way the Earth's atmosphere traps some of the energy from the Sun.

Human activities such as burning fossil fuels like coal, oil and natural gas are increasing the amount of carbon dioxide (CO2), the main greenhouse gas responsible for global warming. Carbon-absorbing forests are also being cut down.

The concentration of CO2 in the atmosphere is now higher than at any time in the last 800,000 years and reached a record high in May 2015. But 2016 marked five consecutive years of CO2 increases of at least two parts per million.

Scripps CO2 Program, data from the Mauna Loa Observatory

3. What are the effects?

Arctic sea ice melt

Higher temperatures, extreme weather events and higher sea levels are all linked to a warming climate and could have a drastic effect on the world's regions.

Since 1900, sea levels have risen by on average about 19cm globally. The rate of sea-level rise has accelerated in recent decades, placing a number of islands and low-lying countries at risk.

The retreat of polar ice sheets is an important contributor to this rise.

Arctic sea ice is also shrinking because of higher temperatures, though it makes little contribution to raised sea levels.

An area of sea ice roughly 10 times the size of the UK has been lost when the current day is compared with average levels from the early 1980s.

Arctic sea ice min. extent: 1980, 7.8 million sq km. 2015, 4.6 million sq km

Source: National Snow and Ice Data Center

4. What does the future hold?

Higher temperatures and more extreme weather

The scale of potential impacts is uncertain.

The changes could drive shortages in freshwater, bring about major changes in food production conditions and cause a rise in the number of casualties from floods, storms, heat waves and droughts.

This is because climate change is expected to increase the frequency of extreme weather events - however linking any single event to global warming is complicated.

Projected temperature change (1986-2005 to 2081-2100)

If greenhouse gas emissions peak between 2010-2020 and then decline substantially (RCP2.6)

If greenhouse gas emissions continue to rise throughout the 21st century (RCP8.5)

Source: International Panel on Climate Change - Fifth Assessment Report (AR5)

5. What can be done?

World's top ten greenhouse gas emitters

The top 10 greenhouse gas emitters make up over 70% of total emissions

Source: Carbon Brief, figures are for 2012

6. Limiting the damage

By the end of October 2015, 146 countries had submitted national climate plans on curbing emissions that are expected to form the cornerstone of a binding, global treaty on climate change.

According to a UN report, submissions in their current form point to a rise of 2.7°C above pre-industrial levels by 2100.

Scientists have determined that if temperature rises surpass 2°C, this will lead to substantial and dangerous climate impacts, which will hit the world's poor in particular.

Average warming (°C) projected by 2100

Source: Climate Action Tracker, data compiled by Climate Analytics, ECOFYS, New Climate Institute and Potsdam Institute for Climate Impact Research.

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Six graphics that explain climate change as world leaders gathered in Paris for COP21.

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Climate change describes a change in the average conditions in a region over a long period of time.

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What’s Really Warming the World? Climate deniers blame natural factors; NASA data proves otherwise

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And it's large countries, like the United States, contributing the most to climate pollution.

Before the humanitarian workers came to his village just outside of Maseru, Lesotho, 24-year-old Makalo Makara and his neighbors mistook climate change for divine punishment.

"We thought what was happening here was a calamity of God," he tells Teen Vogue, poking a wooden staff at a hard patch of dirt. "I have been a herder almost my whole life. I started when I was 8. I would go after school." Like many other young men his age in Lesotho, to step into the profession of herding is considered a rite of passage into manhood.

In the morning, Makalo gets up before the sun with his seven cows and walks until dark while they graze. He does this in every type of weather: rain, sun, or, in recent years, occasionally abrupt snow.

It was only a few years ago that he started to see a marked difference in the soil and grass in his village because of the erratic change in weather. The rainfall, which for most of his life ushered in the planting season in September, has become unpredictable. "The rains are late this year," he says, pointing at a barren patch of dirt that in years past has been speckled with green buds by now. "It affects the way we till the land and my herd doesn't have enough to eat now. Because they don't have enough to eat, [the cattle] are getting thinner and it's harder to use them for plowing." He gestures at a bull standing feet away, whose ribs are showing through a mat of bristled hair.

Lesotho is a country where more than 70% of people are dependent on just 10% of arable land, whether for commerce or to feed their families. Countries with large economies have long been the largest contributors to climate change that threatens the livelihoods of those everywhere, but a broader awareness about the issue within developing countries and their ability to act against it has been a more recent development.

Makalo's testimony is one of many, another page in the endless story of climate change and the impact caused by neglect of the world's second-largest climate polluter: the United States. In November 2017, Syria became the latest country to sign the Paris climate accord, leaving the United States as the only country to proclaim it will not align with the landmark deal. The Trump administration's decision to pull out of the agreement in June of 2017 has been felt worldwide, causing a ripple effect in countries like Lesotho, where the effects of climate change are felt the hardest. "This has been very disappointing for us for several reasons," said Moeketsi Majoro, minister of finance to Lesotho. "It sends a damaging message that the U.S. cannot be counted upon to deliver leadership in matters of global importance. So we are wondering and other countries are asking, can we still count on the U.S. at all?"

Lesotho isn't a country popularly known to the West. Nicknamed "the Kingdom in the Sky" and surrounded by South Africa on all sides, its mountainous landscape covers a space slightly larger than the state of Vermont. Farmers and herders here, similar to many other African countries, are waging war against the elements. When the delayed rains do come, they appear with increasing force that often wash away the nutrient-rich topsoil necessary for most plants to grow.

At the current rate, Lesotho is losing 3-5% of its topsoil every year. "It looks minuscule, but it's actually a huge amount and it's expected to get worse," Eshan Rizvi, who runs the Natural Resource Management Program for Catholic Relief Services (CRS) in country, tells Teen Vogue. He's worked in the field for 12 years to help communities become more resilient in the face of climate change. Citing findings from a recent CRS study on soil degradation, Ehsan says, "soil-loss rates are going to increase because of high temperature, less vegetation cover, and more intense rainfall."

While Lesotho battles a slow crawl to the death of its land, its figurative big brother, South Africa, fights a much more urgent war. Day Zero is tentatively scheduled for July 9 in the port city of Cape Town, South Africa's second-most populous area. It's the moment when city officials will cut off the water to businesses and homes in an effort to save what little is left. Roughly 4 million residents will have to go to one of around 200 water collection points where they will be rationed just 25 liters (about 6.6 gallons) a day. Now in the third year of the worst drought in a century, Cape Town has a water system that has long relied on rain water, rendering locals helpless.

"What is happening in Cape Town is just one example of how climate change is affecting the continent," Dan Shepard, an information officer who works on climate change for the United Nations, tells Teen Vogue. "We are also seeing coastal erosion in Western Africa and changing currents in the water off South Africa, which affects everything from fishing patterns to penguin populations. Climate change exacerbates things, so as temperatures are rising across the continent, it causes more extreme weather, intense droughts, the list goes on."

CRS says it runs climate and agricultural programs in 43 countries reaching over 9 million people. In Lesotho, they are possibly the only organization in-country that is focusing efforts on the youngest generation of agricultural workers to change their behavior to adapt to the changing ecosystem. They start by teaching farmers what climate change is, enlightening communities on how pollution that occurs thousands of miles away is linked to the increasingly erratic and extreme weather patterns at home. Experts also ensure that locals understand not only the global impact of human behavior on their land locally, but also new farming techniques that are more resilient to global climate trends.

For the rising generation of farmers, that means learning how to plant smart crops and use the land as wisely as possible. "As crop production declines with the change in rainfall, people make up for losses by cutting down more trees to expand their land. But that just makes things worse because it releases more carbon into the atmosphere," Ehsan says. "Those trees also prevent water-run off which keeps the soil moist, so they are taking away an important preventative mechanism that they might not know they need."

CRS also trains farmers on how to diversify crops. Corn is often a staple crop because it is hearty and cheap to plant, but farmers are now learning that it isn't good for the soil, Ehsan says. Environmental experts are promoting climate-smart agriculture by recommending intercropping, planting things like beans alongside other crops to put more nitrogen in the soil. Experts also show farmers how to rotate their crops, making them more resistant to pests. "All of this is good insurance against [the changing] weather, and people get excited about it. They see the economic returns," Ehsan says.

CRS is also arming Makalo and his fellow herd boys with an unlikely tool that both helps them economically and works to reduce the impact of climate change on the land: seeds for trees. Using apple, peach, and acacia seedlings, herder communities are trained to create nurseries that grow the trees, which they sell to the government. The Ministry of Forestry, Range and Conservation (MFRC) then plants the trees in local areas as part of an effort to restore the degraded ecosystems.

The success of the new agriculture practices is clear. "It's a win-win with long lasting impact," Ehsan says. "Farmers get another way to make money, they learn importance of trees in fighting climate change, while helping to restore and protect their land in the process."

Makalo says after all he's learned about why the land is changing, it's a small relief to know there is something he can do. "For me this is a difficult situation, because those polluters are far away," he says, frustration in his voice. "We have no way to contact them to tell them or speak with them about it. So what we have to do is focus on planting trees, to absorb the carbon emissions. We have to focus on how to be part of the solution here."

To do your part to help counter climate change, address your congressional representative here.

Related: How Climate Change Is Impacting Animals in the Canadian Arctic
Check this out:

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Poor Countries Are Suffering the Most From Climate Change

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Climate-change effects are mainly felt by small, poor countries that rely on a farming economy, such as Lesotho in Africa. It is large countries, like the United States, that are contributing to these negative effects the most.