Global warming facts for kids

Global mean surface temperature change from 1880 to 2019

Places that were warmer (Red) and cooler (Blue) in 2015 than in previous average

In the Northern Hemisphere, unusually hot summers have become more common (relative to 1951–1980 mean), according to Hansen et al. (2012) as a consequence of global warming.

Global warming means the average temperature of Earth's surface, oceans, and air is going up. This change happens over many years. Today, average temperatures are about 1 °C (1.8 °F) higher than before the Industrial Revolution. This period started around 1750, which was during a very cold time called the Little Ice Age. Some parts of the world have warmed more, and some less.

Many scientists think that by the year 2100, temperatures could be 1.5 °C (2.7 °F) to 5 °C (9.0 °F) higher than they were before 1750. The biggest change we see from this warming is that ice caps all over the world are melting. This causes the sea level to rise steadily. Many cities near the ocean might face floods in the 21st century. Most scientists agree that humans are the main cause of global warming.

One of the main reasons for global warming is the increase of carbon dioxide in the atmosphere. This was predicted by Svante Arrhenius over a hundred years ago, building on the work of Joseph Fourier even earlier. When people burn fossil fuels like coal, oil, and natural gas, they release a lot of carbon dioxide into the air. This happens because fossil fuels have a lot of carbon, and burning them combines this carbon with oxygen. Also, when many trees are cut down (deforestation), less carbon dioxide is taken out of the atmosphere by plants.

As the Earth's surface gets hotter, the sea level rises. This happens partly because water expands when it gets warmer. It also happens because warm temperatures make glaciers and ice caps melt. Rising sea levels can cause coastal areas to flood. Weather patterns are also changing, including where and how much rain or snow falls. Deserts might get bigger. Colder areas are warming faster than warm areas. Strong storms could become more common, and farming might produce less food. These changes will not be the same everywhere, and how they affect different areas is still being studied.

People in government and groups like the Intergovernmental Panel on Climate Change (IPCC) are talking about global warming. However, governments, companies, and other people don't always agree on what to do. Some ideas to reduce warming include burning fewer fossil fuels, planting more trees, eating less meat, and storing carbon dioxide underground. Another idea is to shade the Earth from some sunlight (called geoengineering), but we don't fully understand how this might affect weather in other ways. People could also try to adapt to the temperature changes. Agreements like the Kyoto Protocol and Paris Agreement aim to reduce pollution from burning fossil fuels. Most governments have agreed to these, but some people in government think nothing should change. Even gas produced by cows during digestion causes global warming, because it contains a greenhouse gas called methane.

How Earth's Temperature Changes
History of Climate Change Science
How Global Warming Affects Sea Levels
- Cities Threatened by Rising Sea Levels
Related pages
Images for kids
See also

How Earth's Temperature Changes

A graph of temperatures over the past two thousand years from different proxy reconstructions.

Climate change has always happened throughout Earth's history, including times when ice ages came and went. But modern climate change is different because people are adding carbon dioxide to the atmosphere very quickly.

Since the 1800s, people have recorded daily temperatures. By about 1850, there were enough places measuring temperature for scientists to figure out the global average temperature. Compared to before people started burning a lot of coal for industry, the temperature has gone up by about 1 °C (1.8 °F). In 1979, satellites began measuring Earth's temperature from space.

Before 1850, there weren't enough temperature measurements to know exactly how warm or cold it was. Climatologists use "proxy" measurements to guess past temperatures before thermometers existed. This means measuring things that change when it gets colder or warmer. For example, they can cut into a tree and measure the distance between its growth rings. Trees that live a long time can show how temperature and rain changed during their lives.

For most of the past 2000 years, the temperature didn't change much. There were some slightly warmer or cooler times. A famous warm period was the Medieval Warm Period, and a famous cool period was the Little Ice Age. Other proxy measurements, like temperatures taken in deep holes in the ground, mostly agree with tree ring data. Tree rings and boreholes can help scientists understand temperatures back to about 1000 years ago. Ice cores, which are long tubes of ice drilled from glaciers, can show temperatures from as far back as half a million years ago.

The Greenhouse Effect Explained

Fossil fuel related CO₂ emissions compared to five IPCC scenarios. The dips are related to global recessions.

Coal-burning power plants, car exhausts, factory smokestacks, and other human-made sources release about 23 billion tons of carbon dioxide and other greenhouse gases into Earth's atmosphere every year. The amount of CO₂ in the air is about 31% more than it was around 1750. About three-quarters of the CO₂ that people have put into the air in the last 20 years comes from burning fossil fuels like coal or oil. The rest mostly comes from changes in how land is used, such as cutting down trees.

How the Sun Affects Warming

The Sun gets a little bit hotter and colder every 11 years. This is called the 11-year sunspot cycle. This change is so tiny that scientists can barely measure how it affects Earth's temperature. If the sun were causing Earth to warm up, it would warm both the surface and the air high up. But the air in the upper stratosphere is actually getting colder. So, scientists don't think changes in the sun have much effect on current global warming. Also, over hundreds of millions of years, the sun is slowly getting brighter.

Dust and Dirt in the Air

Dust and dirt in the air can come from natural sources like volcanos, erosion, and tiny bits of meteors. Some of this dirt falls out of the air within a few hours. Some of it is so small it becomes an aerosol and can stay in the air for years. These aerosol particles in the atmosphere actually make the Earth colder. So, the effect of dust cancels out some of the warming from greenhouse gases. Even though humans also put aerosols into the air when they burn coal or oil, this only cancels out the greenhouse effect for less than 20 years. The carbon dioxide stays in the atmosphere much longer and keeps warming the Earth.

History of Climate Change Science

Joseph Fourier; first to explain climate change

Svante Arrhenius; believed climate change would take many years

As early as the 1820s, scientists started learning about climate change. Joseph Fourier thought that light from the sun could enter the atmosphere easily, but it couldn't leave as easily. He tried to show that air can absorb infrared radiation and send it back to Earth's surface. Later, in 1859, John Tyndall found that water vapor and CO₂ trap heat waves from the sun. In 1896, Svante Arrhenius tried to prove that it would take thousands of years for the CO₂ from factories to raise Earth's temperature by 5-6°C.

However, in the early 20th century, many people didn't believe this idea because it seemed too simple. In the mid-20th century, scientists discovered that carbon dioxide in the atmosphere had increased by 10% during the 19th century, making it a little warmer. At this time, people thought CO₂ emissions would grow very fast in the future, and that the oceans would soak up any extra greenhouse gases. In 1956, Gilbert N. Plass argued that greenhouse gas emissions would indeed affect Earth's temperature and that ignoring them would be a mistake. Soon after, scientists from different fields began working together to understand greenhouse gas emissions and their effects. As technology improved, by the 1980s, there was clear proof of rising CO₂ levels. An ice core, obtained by drilling deep into ice sheets, provided strong evidence that carbon dioxide levels had increased.

How Global Warming Affects Sea Levels

Global warming means that the ice sheets in Antarctica and Greenland are melting. Also, the oceans are expanding as they get warmer. A scientific paper in Science suggested that recent climate change would still cause a 6 meters (20 ft) sea-level rise, even if greenhouse gas emissions were reduced in 2015.

Low-lying areas like Bangladesh, Florida, the Netherlands, and other regions could face huge floods.

Cities Threatened by Rising Sea Levels

Places that would be flooded by a 6 meters (20 ft) sea level rise

Many cities are ports and are at risk of flooding if the current sea level keeps rising.

These cities, and others, have either started trying to deal with rising sea levels and related storm surges, or they are discussing what to do:

London
New York City
Norfolk, Virginia, in the Hampton Roads area of the United States
Southampton
Crisfield, Maryland, United States
Charleston, South Carolina
Miami, Florida, has been called "the number-one most vulnerable city worldwide" because of possible damage from storm floods and sea-level rise.
Saint Petersburg
Sydney, Australia
Jakarta
Thatta and Badin, in Sindh, Pakistan
Malé, Maldives
Mumbai, Buenos Aires, Los Angeles, Rio de Janeiro

All other cities along the coast are also in danger.

Images for kids

Data has been cherry picked from short periods to falsely assert that global temperatures are not rising. Blue trendlines show short periods that mask longer-term warming trends (red trendlines). Blue dots show the so-called global warming hiatus.
This 1912 article succinctly describes the greenhouse effect, focusing on how burning coal creates carbon dioxide that causes climate change.
Ecological collapse. Bleaching has damaged the Great Barrier Reef and threatens reefs worldwide.
Extreme weather. Drought and high temperatures worsened the 2020 bushfires in Australia.
Arctic warming. Permafrost thaws undermine infrastructure and release methane, a greenhouse gas.
Habitat destruction. Many arctic animals rely on sea ice, which has been disappearing in a warming Arctic.
Pest propagation. Mild winters allow more pine beetles to survive to kill large swaths of forest.
Environmental migration. Sparser rainfall leads to desertification that harms agriculture and can displace populations. Shown: Telly, Mali (2008).
Agricultural changes. Droughts, rising temperatures, and extreme weather negatively impact agriculture. Shown: Texas, US (2013).
Tidal flooding. Sea-level rise increases flooding in low-lying coastal regions. Shown: Venice, Italy (2004).
Storm intensification. Bangladesh after Cyclone Sidr (2007) is an example of catastrophic flooding from increased rainfall.
Heat wave intensification. Events like the June 2019 European heat wave are becoming more common.