The Earth’s climate system is a complex, interactive process made up of the atmosphere, land, snow and ice, oceans and living things. Two factors change the atmosphere -- natural phenomena like volcanic eruptions and human-induced increases in greenhouse gases like carbon dioxide.

In 2007, the fourth report of the Intergovernmental Panel on Climate Change found that the climate system is warming, and scientists are more than 90 percent sure that human-induced greenhouse gas concentrations are a primary cause. On May 31, President Bush proposed a new international framework to reduce greenhouse gas emissions. The initiative is part of a larger U.S. effort to work with developed and developing nations to meet the global challenge of climate change.

On September 27-28 in Washington, the Major Economies Meeting on Energy Security and Climate Change is the first of a series of meetings that will bring world leaders together to reduce global greenhouse gas emissions, increase energy security and efficiency and sustain economic growth.