Climate Change
In their most recent report, the IPCC concluded that it is unequivocal that the average temperature of Earth’s surface has warmed recently and it is very likely (greater than 90% probability) that most of this global warming is due to increased concentrations of humangenerated greenhouse gases.
Several different types of gases in the atmosphere warm the planet by trapping energy that would otherwise be emitted to space. These ‘greenhouse gases’ include water vapor, carbon dioxide, methane, ozone, nitrous oxide, and several fluorine- and chlorine-containing gases. Of the greenhouse gases that are increasing in atmospheric concentration as a direct result of human activities, carbon dioxide is contributing most to the recent warming. The globally averaged concentration of carbon dioxide in the atmosphere has increased from about 280 parts per million (ppm) in the 18th century to 383 ppm in 2007. Emissions of carbon dioxide from fossil fuel use and from the effects of land use change are the primary sources of this increase.
The current atmospheric concentration of carbon dioxide greatly exceeds the natural range of the last 650,000 years (180 to 300 ppm) as determined from ice cores. Indeed, the atmospheric levels of all major greenhouse gases have also increased significantly in the past century (Scientific Assessment of the Effects of Climate Change on the United States-Naitonal Science and Technology Council, 2008)
