Global Warming is the rising of the average temperature of Earth's atmosphere and oceans due to the last 190 years of intense human fossil fuel energy use and deforestation.

Scientists often use the term "climate change" instead of global warming. This is because as the Earth's average temperature climbs, winds and ocean currents move heat around the globe in ways that can cool some areas, warm others, and change the amount of rain and snow falling. As a result, the climate changes differently in different areas. Over the past 50 years the average global temperature has increased at the fastest rate in recorded history.

The 10 hottest years on record have all occurred since 1990. Scientists say that unless we curb global warming or greenhouse gas emissions, average U.S. temperatures could be 3 to 9 degrees higher by the end of the century.

To understand the process of global warming you must understand how the greenhouse effect controls the earth's temperature.

Greenhouse Effect

The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse.

First, sunlight shines onto the Earth's surface, where it is absorbed and then radiates back into the atmosphere as heat. In the atmosphere, “greenhouse” gases trap some of this heat, and the rest escapes into space. The more greenhouse gases are in the atmosphere, the more heat gets trapped. Interactive diagram on the greenhouse effect

Common Greenhouse gases include:

• water vapor
• carbon dioxide
• atmospheric methane
• nitrous oxide
• ozone
• chlorofluorocarbons

Fossil fuels

Fossil fuels include coal, petroleum-gasoline, diesel, jet fuel, and natural gas which contain high percentages of carbon. Fossil fuels were formed by dead matters from hundreds of millions of years ago. Over this time period cooking under earth's shifting surface and pressure became the fuels we burn today in cars, for electricity, and to cook.  For more information, read The Energy Story.

Impacts

See interactive map on climate change impacts 

• Extreme Weather events such as more frequent heat waves, droughts, flood, intense hurricanes, wildfires
• Melting of polar ice caps and glaciers
• Rising sea levels
• Increase in infectious diseases carried by mosquitoes and rodents
• Smog pollution and air pollution related disease exacerbation
• Famines, lowered food production, water shortages
• Species extinction and biodiversity loss
• Cultural genocide

For more information, read Thirteen Tipping Points.