![]() ![]() If current emission rates continue then temperature rises will surpass 2.0 ☌ (3.6 ☏) sometime between 20, which is the level the United Nations' Intergovernmental Panel on Climate Change (IPCC) says is "dangerous". Īccording to Berkeley Earth, average global surface temperature has risen by more than 1.2 ☌ (2.2 ☏) since the pre-industrial (1850–1899) period as a result of greenhouse gas emissions. Methane emissions originate from agriculture, fossil fuel production, waste, and other sources. Additional contributions come from cement manufacturing, fertilizer production, and changes in land use like deforestation. The vast majority of carbon dioxide emissions by humans come from the combustion of fossil fuels, principally coal, petroleum (including oil) and natural gas. Methane causes most of the remaining warming and lasts in the atmosphere for an average of 12 years. Carbon dioxide is causing about three quarters of global warming and can take thousands of years to be fully absorbed by the carbon cycle. Human activities since the beginning of the Industrial Revolution (around 1750) have increased atmospheric methane concentrations by over 150% and carbon dioxide by over 50%, up to a level not seen in over 3 million years. Without greenhouse gases, the average temperature of Earth's surface would be about −18 ☌ (0 ☏), rather than the present average of 15 ☌ (59 ☏). The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by water vapor ( H 2O), carbon dioxide (CO 2), methane ( CH 4), nitrous oxide ( N 2O), and ozone ( O 3). ![]() What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. Greenhouse gases are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Three important greenhouse gases are shown symbolically in this image: water vapor, carbon dioxide and methane. Greenhouse gases trap some of the heat that results when sunlight heats the Earth's surface. Gas in an atmosphere that absorbs and emits radiation at thermal infrared wavelengths ![]()
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