Global warming

Global mean surface temperatures 1856-2004

Global warming is a slow but steady rise in Earth's surface temperature. Temperatures today are 0.74 °C (1.33 °F) higher than 150 years ago. Some people think that the warming is because of people burning fossil fuels like coal and oil. Some also think that humans are cutting down too many of the earth's forests, a process known as deforestation. Most major governments and science groups agree with these ideas.

If the earth's temperature becomes hotter the sea level will also become higher. This is partly because water expands when it gets warmer. It is also partly because warm temperatures make glaciers melt. The sea level rise may cause coastal areas to flood. Weather patterns, including where and how much rain or snow there is, will change. Deserts will probably increase in size. Colder areas will warm up faster than warm areas. Strong storms may become more likely and farming may not make as much food. These effects will not be the same everywhere. The changes from one area to another are not well known.

People in government have talked about global warming. They do not agree on what to do about it. Some things that could reduce warming are to burn less fossil fuels, adapt to any temperature changes, or try to change the Earth to reduce warming. The Kyoto Protocol tries to reduce pollution from the burning of fossil fuels. Most governments have agreed to it. Some people in government think nothing should change.

Temperature changes

See also: Temperature record of the past 1000 years

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

Since the 1800s, people have recorded the daily temperature. By about 1850, there were enough places measuring temperature so that scientists could know the global average temperature. From 1920 to 1940, the temperature got warmer. From 1940 to 1970, the temperature got slightly cooler. From 1970 to today, the average temperature for the world has increased by about 0.6 ± 0.2 °C. Starting in 1979, satellites started measuring the temperature of the Earth.

Before 1850, there were not enough temperature measurements for us to know how warm or cold it was. Scientists use proxy measurements 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 rings are. Trees that live a long time can give us an idea of how temperature and rain have changed while it was alive. For most of the past 2000 years the temperature didn't change much. There were some times where the temperatures were a little warmer or cooler. 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. Other proxy measurements like the temperature measured in deep holes mostly agree with the tree rings. Tree rings and bore holes can only help scientists work out the temperature until about 1000 years ago. Ice cores are also used to find out the temperature back to about half a million years ago. Ice cores show that the Earth goes through cycles of ice ages about every 100,000 years.

The greenhouse effect

See the main article: Greenhouse effect

Carbon dioxide during the last 400,000 years and the rapid rise since the Industrial Revolution

Coal-burning power plants, car exhausts, factory smokestacks, and other man-made waste gas vents give off about 23 billion tons of carbon dioxide and other greenhouse gases into the Earth's atmosphere each year. The amount of CO₂ in the air is about 31% more than it was around 1750. This is a huge amount higher than at any time during the last 425,000 years, the information for which has been collected from ice cores. People believe that CO₂ values this high were last reached 40 million years ago. About three-quarters of the CO₂ that people have put in the air during the past 20 years are due to burning fossil fuel like coal or oil. The rest mostly comes from changes in how land is used, like cutting down trees.

The Sun

See the main article: Sun

The sun gets a little bit hotter and colder every 11 years. This is called the 11-year sunspot cycle. The change is so small that scientists can barely measure how it affects the temperature of the Earth. If the sun was causing the Earth to warm up, it would warm up both the surface and high up in the air. But the air up very high is actually getting colder, so scientists don't think the sun has much of an effect.

Dust and dirt

People also make a lot of dust and dirt. Some of this dirt is large, so it falls out within a few hours. Some is so small that it could stay in the air for years. This big dirt is still very small. It's about the width of a human hair. The big dirt does not stay in the air for years though because rain hits it and brings it to the surface. It actually only stays in the air for about 7 days. But this is still a long time, and can cause changes in the temperature of the Earth.

Possible responses

There are two main ways that people think global warming can be stopped. The first is to stop putting greenhouse gases in the atmosphere. Many people have tried to get countries to stop emitting greenhouse gases. The Kyoto Protocol was signed in 1997. It was supposed to reduce the amount of greenhouse gases in the atmosphere to below their levels in 1990. As of 2010, the Kyoto Protocol has not worked in reducing greenhouse gas levels. Carbon dioxide levels today are the highest they have been since the start of the Industrial Revolution.

The second is for people to change how they live because of any changes that global warming will bring. The amount of money a country has will affect how easily it adapts. Rich countries will be able to change more easily, while poor countries may not be able to change. According to the Natural Resources Defense Council, there are several other things that can be done to help with global warming. Driving cars that get better gas mileage, are hybrid, or simply electrical is one major way to stop emitting so much greenhouse gas. People also need to speak out and get their lawmakers to help pass stricter laws about pollution. Using energy efficient appliances, "weatherizing" the home, and choosing energy companies that are "green" are a few other ways people can help stop global warming ("How To" para. 8).

Etymology

The term global warming was probably first used in its modern sense on 8 August 1975 in a science paper by Wally Broecker in the journal Science called "Are we on the brink of a pronounced global warming?". Broecker's choice of words was new and represented a significant recognition that the climate was warming; previously the phrasing used by scientists was "inadvertent climate modification," because while it was recognized humans could change the climate, no one was sure which direction it was going. The National Academy of Sciences first used global warming in a 1979 paper called the Charney Report, it said: "if carbon dioxide continues to increase, we find no reason to doubt that climate changes will result and no reason to believe that these changes will be negligible." The report made a distinction between referring to surface temperature changes as global warming, while referring to other changes caused by increased CO₂ as climate change.

Global warming became more widely popular after 1988 when NASA climate scientist James Hansen used the term in a testimony to Congress. He said: "global warming has reached a level such that we can ascribe with a high degree of confidence a cause and effect relationship between the greenhouse effect and the observed warming." His testimony was widely reported and afterward global warming was commonly used by the press and in public discourse.

Further reading

• Why you should sweat climate change March 1, 2013 USA Today
• Report Blames Climate Change for Extremes in Australia March 4, 2013 The New York Times