CI-greenhouse-gases-2012 - Greenhouse Major Greenhouse...

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INDICATORS IN THIS CHAPTER Greenhouse U.S. Greenhouse Gas Emissions Global Greenhouse Gas Emissions Atmospheric Concentrations of Greenhouse Gases Major Greenhouse Gases Associated with Human Activities Greenhouse gas How it’s produced Average lifetime in the atmosphere 100-year global warming potential Carbon dioxide Emitted primarily through the burning of fossil fuels (oil, natural gas, and coal), solid waste, and trees and wood products. Changes in land use also play a role. Deforestation and soil degradation add carbon dioxide to the atmo- sphere, while forest regrowth takes it out of the atmosphere. see below* 1 Methane Emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and agricultural prac- tices and from the anaerobic decay of organic waste in municipal solid waste landfills. 12 years 21 Nitrous oxide Emitted during agricultural and industrial activi- ties, as well as during combustion of fossil fuels and solid waste. 114 years 310 Fluorinated gases A group of gases that includes hydrofluorocar- bons, perfluorocarbons, and sulfur hexafluoride, among other chemicals. These gases are emitted from a variety of industrial processes and com- mercial and household uses, and do not occur naturally. Sometimes used as substitutes for ozone-depleting substances such as chlorofluoro- carbons (CFCs). A few weeks to thousands of years Varies (the highest is sulfur hexafluo- ride at 23,900) This table shows 100-year global warming potentials, which describe the effects that occur over a period of 100 years after a particular mass of a gas is emitted. EPA uses global warming potentials from the Intergovernmental Panel on Climate Change’s (IPCC’s) Second Assessment Report, 1 as countries have agreed to do under current international guidelines within the United Nations Framework Convention on Climate Change (UNFCCC). Lifetimes come from the IPCC’s Fourth Assessment Report. 2 * Carbon dioxide’s lifetime is poorly defined because the gas is not destroyed over time, but instead moves among different parts of the ocean– atmosphere–land system. Some of the excess carbon dioxide will be absorbed quickly (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments. 10
E nergy from the sun drives the Earth’s weather and climate. The Earth absorbs some of the energy it receives from the sun and radiates the rest back toward space. However, certain gases in the atmosphere, called greenhouse gases, absorb some of the energy radiated from the Earth and trap it in the atmosphere. These gases essentially act as a blanket, mak- ing the Earth’s surface warmer than it otherwise would be.

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