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What Is Climate Change?

Earth's Climate is Changing

We can see and measure climate changes  around the world. Global temperature is warming, weather patterns are changing, polar ice is melting, and sea level is rising. 

Climate  has changed throughout Earth's long history. But this time is different. Worldwide temperatures are rising higher and faster than anytime we know of in the past. And this time, human activities are causing it. 

Can we slow this global warming by changing the way we live? Yes, there is still time. But it will take everyone working together around the world.

smoke stacks

Human activity is causing the climate to warm.

3 polar bears

Climate change is threatening plants, animals, and their habitats.

The Atmosphere Keeps Our Planet Warm

Throughout our planet's history, global temperatures have risen and fallen naturally. But it has never become too hot or too cold for life to exist. That's because Earth  is wrapped in its own protective blanket of air, a mixture of gases called the atmosphere.

The atmosphere lets in energy from the Sun . Gases in the atmosphere absorb and keep just enough heat for plants and animals to live. This process is called the greenhouse effect, because the atmosphere holds in heat like the clear walls of a greenhouse. 

The heat-absorbing gases in the atmosphere are called greenhouse gases. Some of the main greenhouse gases include carbon dioxide , water vapor, methane, and ozone. And the more greenhouse gases there are, the warmer Earth gets.

blue sky with white clouds

The atmosphere has kept Earth livable for over 3 billion years. 

sea ice

Without the atmosphere, Earth's entire surface would be frozen all the time. 

Carbon Dioxide in the Atmosphere is Rising

Human actions are causing Earth to warm by increasing the amount of carbon dioxide in the atmosphere. Today, there's more carbon dioxide in the air than anytime in at least 800,000 years. That's 8,000 centuries

When we burn fossil fuels , we are rapidly releasing carbon that had been locked within Earth into the atmosphere. This carbon combines with oxygen in the air to form carbon dioxide. 

Another way humans are increasing carbon dioxide levels is by cutting down trees. Trees are like sponges that remove carbon dioxide from the air through photosynthesis. To make matters worse, we also burn trees. This quickly releases carbon dioxide into the atmosphere.

traffic lights

Most of our electricity comes from coal.

traffic jam on highway

Humans refine oil to produce gasoline and diesel fuel.

The Climate System is Complex

The climate system can be complicated to study. That's because it's an interaction between the ocean, atmosphere, land, ice, and life. 

To study climate, scientists analyze temperature readings from weather  stations around the world. And to measure the temperature and chemistry of the ocean, scientists rely on information from ships, satellites, and buoys spread across the oceans.

To understand how climate is changing, scientists need to look back into Earth's past — back hundreds, thousands, and even millions of years. For this information, they find clues from Earth itself, like tree rings, deep-sea sediment, corals, and glacial ice.

Buoy in ocean near ship

Buoys measure the ocean's temperature and chemistry.

scientists taking ice core

Ice cores hold clues about past temperatures and CO2 concentrations.

Weather May Become More Extreme

Climate change is already affecting the weather. It is having a big impact on our world and all its living things, including us. 

Heat waves have become more frequent and more intense. These long periods of heat threaten crops, animals, roads, and people.

Hurricanes  could become more powerful, driven by warmer oceans. This puts coastal areas at greater risk. 

Intense rainstorms and flooding will become more common. As ocean temperatures rise, so does evaporation. Extra water vapor in the air leads to more rain and snow. 

Droughts are becoming more intense and happening more often in drier areas. Hotter soils get drier faster. There is less water in the soil to evaporate into the air, so there is less rainfall.

raft of flood rescuers approaching home partially under water

Heavier rainstorms can bring flash floods, especially near rivers.

dry cracked earth

There may be longer, hotter summers, causing more droughts and wildfires.

Melting Ice Affects the Whole World

As temperatures warm, ice is melting at Earth's poles. Its impact will be global. 

Sea levels on the rise: Melting is opening up the way for Antarctic and Greenland ice sheets to flow from land into the ocean. As these reservoirs of freshwater enter the ocean, sea levels will rise. Over the next century, many coastal areas may be flooded and even submerged.

Habitats harmed: Melting Arctic  sea ice and permafrost (frozen land) is disturbing the places where many polar animals hunt, nest, and breed.

Even warmer temperatures: Polar snow and ice reflect much of the Sun's energy  back into space. As Arctic sea ice shrinks, less energy is reflected and more is absorbed by the ocean, making temperatures warmer. As temperatures rise, more ice will melt and the ocean absorbs even more heat. This further increases global warming.

sea ice covering the Arctic as of 1979

The first satellite image of Arctic sea ice was taken in September 1979.

sea ice covering the Arctic as of 2007

In September 2007, Arctic sea ice covered an area 50% smaller than 1979.

Changing Oceans Change Climate

The oceans help control climate by absorbing huge amounts of heat and carbon dioxide from the atmosphere. As climate changes, so will ocean waters. 

Threaten marine animals: Over the past 200 years, ocean waters absorbed about 30 percent of the carbon dioxide released by humans. This has changed the chemistry of the water , making it less basic. In other words, the ocean is "acidifying." This could make it harder for shell-forming organisms to grow their shells. Eventually, they could disappear.

Disrupt food chains: Changes in ocean water threaten populations of phytoplankton . These microscopic plants form the base of the ocean's complex food chains, so this could affect animals throughout the ocean. 

Increased carbon dioxide in the atmosphere: As plants, phytoplankton use carbon dioxide and sunlight to make their own food through photosynthesis. If their numbers decrease, the oceans won't be able to absorb as much carbon dioxide from the atmosphere.

cora reef teaming with life

If coral reefs die, species that rely on them for food and shelter are threatened, too. 

periwinkle snails

The periwinkle snail uses carbon to thicken its shells to fend off predators.

Together, We Can Slow Climate Change

Each of us can lower the amount of greenhouse gases we put into the atmosphere. This means using less energy! We can: 

  • Take the bus, ride a bike, or carpool.
  • Turn off lights and electronics when you're not using them. 
  • Recycle and reuse products, since making new stuff requires more energy.
  • Plant a tree. Trees absorb carbon dioxide from the air. 


Communities and governments can switch to "clean" energy sources like solar , wind , nuclear , and geothermal power

There's no single answer to stopping climate change. It's going to take different solutions, with everyone working together.

girl holding reusable shopping bag

Next time you shop, bring your own bag instead of taking a new plastic bag.

house with solar panels on roof

Many "green" buildings use solar panels to generate electricity with sunlight. 

Image Credits:

Photos: smokestack, © Ken W. Kiser; polar bears, courtesy of US Department of the Interior; sky,  Vanessa Van Ryzin; ice, © USGS; traffic light, public domain courtesy of Open Grid Scheduler / Grid Engine; traffic, © Tony Tremblay; buoy, courtesy of T. P. Walker / NOAA (CC BY 2.0); scientists and ice core, © AMNH; flood, © USGS; Arctic ice cover, © NASA; coral reef, courtesy of Julie Bedford, NOAA PA (CC BY 2.0); periwinkle snail, © USGS; girl with bag, © AMNH; house with solar panels, © Taggart Construction.