# Global warming

Some things global warming makes worse (clockwise from top left): Wildfires, droughts, and dead coral killed by the ocean getting more hot and acidic.
 Places that have become warmer (red) and cooler (blue) over the past 50 years
 Earth's average temperature has increased since the Industrial Revolution.
**Global warming** or **global heating** is the rise in temperature of Earth’s air and oceans. It is happening mainly because humans burn coal, oil, natural gas, and cut down forests.

Average temperatures today are about 1.3 °C (2.3 °F) higher than before people started burning a lot of coal around 1750. By the year 2100 temperatures will very likely be 1.5 °C (2.7 °F) to 4.5 °C (8.1 °F) higher than before 1900.There will be more warming in the Arctic, on land and in the northern half of the world.

Although climate has changed before people started burning a lot of stuff, the last time the Earth was this hot was probably more than 100 thousand years ago.

Global warming is probably getting faster. It is making more heat waves and wildfires, and melting the ice around the North Pole.

The present global warming is mostly because of people burning things, such as gasoline for cars and natural gas to keep houses warm. But the heat from the burning itself only makes the world a tiny bit warmer: *it is the carbon dioxide from the burning which is the biggest part of the problem*. Among greenhouse gases, the increase of carbon dioxide in the atmosphere is the main cause of global warming. Svante Arrhenius predicted this more than a hundred years ago. Arrhenius confirmed the work of Joseph Fourier 200 years ago.

When people burn fossil fuels like coal, oil and natural gas this adds carbon dioxide to the air, since fossil fuels contain lots of carbon and burning means joining most of the atoms in the fuel with oxygen. When people cut down many trees (deforestation), this means less carbon dioxide is taken out of the atmosphere by those plants. Animals who have four places in their stomachs, like cows and sheep, also cause global warming, because their burps contain a greenhouse gas called methane. Although methane remains in the atmosphere for a shorter time than CO₂—roughly 12 years compared to centuries—it has a much stronger heat-trapping ability, making it a critical target for short-term climate mitigation. Reducing methane emissions can quickly slow the rate of global warming. According to the Intergovernmental Panel on Climate Change (IPCC), human-caused methane emissions have increased dramatically since pre-industrial times, accounting for roughly 30% of the rise in global temperatures since the 1800s.

As the Earth's surface temperature becomes hotter, the sea level rises. This is partly because water over 4 °C (39 °F) expands when it gets warmer. It is also partly because warm temperatures make glaciers and ice caps melt. The sea level rise causes coastal areas to flood. Weather patterns, including where and how much rain or snow falls, are changing. Deserts will probably become larger. Colder areas will warm up faster than warm areas. Strong storms may become more likely and farming may not produce as much food. These changes will not be the same everywhere.

In the Paris Agreement, almost all countries agreed to keep temperature rise below 2 °C (3.6 °F), but current plans are not enough to limit global warming as much. People in government and the Intergovernmental Panel on Climate Change (IPCC) are talking about global warming. But governments, companies, and other people do not agree on future plans. Some things that could reduce warming are to burn less fossil fuels, grow more trees, eat less meat, and put some carbon dioxide back in the ground. People could adapt to some temperature change. A few people think nothing should change.

## Temperature changes

A graph of temperatures over the past two thousand years. The so-called Medieval Warm Period and Little Ice Age were regional phenomena, and were not experienced worldwide.
Climate change has happened constantly over the history of the Earth, including the coming and going of ice ages. But modern climate change is different because people are putting carbon dioxide into the atmosphere more quickly than before.

Since the 1800's, people have recorded daily temperatures. By about 1850, there were enough places measuring temperature so that scientists could know the global average temperature. In 1979, satellites started measuring the temperature of the Earth.

Climatologists measure other things to try to figure out past temperatures before there were thermometers. This means measuring things that change when it gets colder or warmer. One way is to cut into a tree and measure how far apart the growth rings are. This is called dendrochronology. Trees that live a long time can give us an idea of how temperature and rain changed while they were alive.

For most of the past 2000 years the average temperature of the world didn't change much. There were some times where the temperatures were a little warmer or cooler in some places. One of the most famous warm times was the Medieval Warm Period and one of the most famous cool times was the Little Ice Age (not really an ice age). Tree ring dating can only help scientists work out the temperature back to about 10,000 years ago. Ice cores are used to find out all the temperature back to almost a million years ago, and for some times to over 4 million years ago.

### Greenhouse gases

Fossil fuel related CO2 emissions compared to five IPCC scenarios. The dips are related to global recessions.
There are several greenhouse gases that cause the Earth to warm. The most important one is carbon dioxide (CO2). CO2 comes from power plants which burn coal and natural gas to make electricity. Cars and trucks which burn gasoline or diesel put CO2 in the air through their exhaust. Airplanes do too and their contrails make warming worse. About 35 billion tons of carbon dioxide are released into the Earth's atmosphere each year. The amount of CO2 in the air is about 50% more than it was around 1750. About three-quarters of the CO2 that people have put in the air during the past 20 years is from burning fossil fuel like coal or oil. The rest mostly comes from changes in how land is used, like cutting down trees.

The second most important greenhouse gas is methane. A tonne of methane is much more warming than a tonne of CO2 but methane stays in the atmosphere for only about ten years. About 40% comes from nature, like wetlands; and the rest is because of humans, cows, landfill and leaks when oil and gas are produced.

### Smoke and dust

Dust in the air may come from natural sources such as volcanos, erosion and meteoric dust. Some of this dust falls out within a few hours. Some is aerosol, so small that it could stay in the air for years. The aerosol particles in the atmosphere make the earth colder. The effect of dust therefore cancels out some of the effects of greenhouse gases. Even though humans also put aerosols in the air when they burn coal or oil this only cancels out the greenhouse effect of the fuel burning for less than 20 years, The carbon dioxide stays in the atmosphere much longer and keeps on warming the earth.

Smoke and dust near the ground is bad, because when people breath it they might get ill, like cancer. But some people say that in a climate change emergency the Earth could be kept cool by reflecting some sunlight back into space, for example by putting dust very high in the air or making clouds whiter. They say this would give more time to do a proper fix. This is so easy and cheap that even a middle-size country could do it. But there are a lot of problems: for example it might be good for that country but bad for some other countries.

## How global warming makes people ill

Global warming makes heatwaves. Heatwaves are dangerous because very hot weather can kill old or sick people. But fewer people will die from cold. It is very hard to add up how many people will die early, but generally it will be poor people who die from heat, for example if they have not got enough money to buy an air-conditioner.

## Extreme weather

Heatwaves can dry out forests so they burn more easily, like in Los Angeles in 2024.

Sometimes there is not enough rain, so it is difficult for farmers to grow vegetables. But sometimes there is too much rain, so floods wash away houses. Global warming is making tropical storms stronger, and because the sea is higher they are more likely to flood cities on the coast.

## Slowing climate change

Some people can do things by themselves to slow climate change, but other things can only be done by people working together in business or government. For example if your gas boiler breaks down you might replace it with a heat pump, but only government can change the taxes on electricity and gas. A business can put 10 million solar panels in fields much more cheaply than a million people can put ten panels on each of their roofs.

A government may help businesses, for example to build factories to make electric vehicles. But in a democracy the government might be voted out of power a few years later and the new government might decide to stop that support. As it takes years to build car factories it is very hard for business to plan ahead if climate policy keeps being changed, like in the United States. To try to make this less of a problem government can create an independent organisation to give long-term advice, like in the United Kingdom.

Sometimes people vote for leaders who want to slow climate change. Most countries try to emit less greenhouse gases, for example by shutting down coal-fired power plants. But some countries want to carry on making a lot of money by selling oil or gas. And some countries are not democracies so it is hard for people to change their leaders.

The Kyoto Protocol was signed in 1997. It was meant to reduce the amount of greenhouse gases in the atmosphere to below their levels in 1990. However, carbon dioxide levels have continued to rise.

Energy conservation is used to burn less fossil fuel, for example people in cold countries can put insulation on their houses to keep them warm so they don’t have to burn so much gas for their central heating. People can also use energy sources that don't burn fossil fuel, like solar panels or electricity from nuclear power or wind power.

Some factories might be able to prevent carbon dioxide from getting out into the atmosphere, for example from making cement. This is called carbon capture and storage (CCS).

## Dealing with impacts of climate change

People can change how they live because of the effect of climate change. This is called adapting to climate change. For example, they can go to places where the weather is better, or build walls around cities to keep flood water out. Or we can make more parks in cities to keep people cool and sponge up a lot of rain.

This costs money, and rich people and rich countries will be able to change more easily than the poor.

## History of climate change science

Joseph Fourier; first to explain climate changeSvante Arrhenius; believed climate change would take many years
As early as the 1820s some scientists were discussing climate change: sunlight heats the surface of the Earth, and Joseph Fourier suggested that some of the heat radiated from the surface is trapped by the atmosphere before it can escape into space. This is called the greenhouse effect.

In 1856 Eunice Newton Foote did tests which showed that the warming effect of the Sun is greater for air with water vapour than for dry air, and that the effect is even greater with carbon dioxide. So she said that "An atmosphere of that gas would give to our earth a high temperature...".

The greenhouse effect and its impact on climate were described in this 1912 *Popular Mechanics* article meant for reading by the general public.
Starting in 1859, John Tyndall showed that nitrogen and oxygen—together totaling 99% of dry air—are transparent to radiated heat. However, water vapour and gases such as methane and carbon dioxide absorb radiated heat and re-radiate that heat into the atmosphere. Tyndall suggested that changes in the concentration of these gases may have caused climatic changes in the past, including ice ages. In 1896, Svante Arrhenius tried to prove that it would take thousands of years for the industrial production of CO2 to raise the Earth’s temperature 5-6°C.

In the mid 20th century, scientists worked out that there was a 10% increase in carbon dioxide in the atmosphere over the 19th century, which made it a bit warmer. It was at this time that people believed the emissions of CO2 would increase exponentially in the future and the oceans would absorb any surplus of greenhouse gases. In 1956, Gilbert N. Plass decided that greenhouse gas emissions would have an effect on the Earth’s temperature. He argued that not thinking about GHG emissions would be a mistake. Soon after, scientists studying all different kinds of science began to work together to figure out the mystery of GHG emissions and their effects. As technology advanced, it was in the 1980s that there was proof of a rise in CO2 levels. An ice core, captured through drilling, provided clear evidence that carbon dioxide levels have risen.

The climate of the Earth will never be absolutely stable because there are small but unpredictable variations in the Earth's orbit about the Sun. In the deep past there have also been large changes in the Earth's atmosphere. For a longer account, see climate change.

## Effects of global warming on sea levels

Sea level is rising because water over 4 °C (39 °F) expands when it gets warmer. Probably more important is the melting of ice sheets. The Antarctica and Greenland ice sheets are melting. Sea level will rise between half and one meter by 2100, and between 2 and 7 meter by 2300.

Low-lying areas such as Bangladesh, Florida, the Netherlands and other areas face massive flooding.

### Cities affected by current sea level rise

Many cities are sea ports and under threat of flooding if the present sea level rises.

These and the other cities have either started trying to deal with rising sea level and related storm surge, or are discussing this, according to reliable sources.

* Rotterdam always was below sea level.
* London Nevertheless, in comparison with most major cities, London is comparatively safe from the Thames. Much has been done over the past to keep control of the river.
* New York City
* Norfolk, Virginia, in Hampton Roads area of United States
* Southampton
* Crisfield, Maryland, United States
* Charleston, South Carolina
* Miami, Florida, has been listed as "the number-one most vulnerable city worldwide" in terms of potential damage to property from storm-related flooding 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 coastal cities are in some danger.

* *What is climate change* National Geographic Kids
* *What is climate change? A really simple guide* BBC

## Related pages

* Carbon neutrality
* Climate change
* Levee (dike)
* Heat wave
* Stern Review
* Pollution
* Intergovernmental Panel on Climate Change
* Greenhouse effect

## Other websites

* The Climate Change Guide easy-to-understand information on Climate Change.