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Vantage to Pomona Heights Chapter 3 230 kV Transmission Line Project FEIS Affected Environment PAGE 3-276 Greenhouse Gas Emissions and Consideration of Climate Change in National Environmental Policy Act Documents.” According to the BLM’s IM No. 2008-171 (BLM 2008), climate change considerations should be acknowledged in Environmental Impact Statement documents. The IM states that ongoing scientific research has identified the potential impacts of human caused greenhouse gas emissions and changes in biological carbon sequestration due to land management activities on global climate. Through complex interactions on a regional and global scale, these greenhouse gas emissions and net losses of biological carbon sinks cause a net warming effect of the atmosphere, primarily by decreasing the amount of heat energy radiated by the earth back into space. Although greenhouse gas levels have varied for millennia, recent industrialization and burning of fossil carbon sources have caused carbon dioxide equivalent (CO2(e)) concentrations to increase dramatically and are likely to contribute to overall global climatic changes. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that “warming of the climate system is unequivocal” and “most of the observed increase in globally average temperatures since the mid-20th century is very likely due to the observed increase in human caused greenhouse gas concentrations” (IPCC 2007). Ongoing scientific research has identified the potential impacts of climate changing pollutants on global climate. These pollutants are commonly called “greenhouse gases.” Greenhouse gases are chemical compounds found in the earth’s atmosphere that absorb and trap infrared radiation, or heat, re-radiated from the surface of the earth. The trapping and build-up of heat in the atmosphere increases the earth’s temperature, warming the planet and creating a greenhouse-like effect (Energy Information Administration [EIA] 2009a). Anthropogenic (human) activities are increasing atmospheric concentrations to levels that could increase the earth’s temperature up to 7.2˚F by the end of the twenty- first century (USEPA 2009a). The principal greenhouse gases emitted into the atmosphere through human activities are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases (USEPA 2010a). Of these four gases, CO2 is the major greenhouse gas emitted (USEPA 2010a; Houghton 2010). For example, CO2 emissions resulting from the combustion of coal, oil, and gas constitute 81 percent of all U.S. greenhouse gas emissions (EIA 2009b). Carbon dioxide enters the atmosphere primarily through the burning of fossil fuels coal, natural gas and oil, and wood products; as a result of land use changes; and the manufacturing of cement. Prior to the industrial revolution, concentrations were roughly stable at 280 ppm, but have increased 36 percent to 379 ppm in 2005, all of which is attributed to human activities (IPCC 2007). Of the remaining three greenhouse gases, CH4 is emitted during the production and transport of fossil fuels, through intensive animal farming, and by the decay of organic waste in landfills. CH4 concentrations have increased 148 percent above pre-industrial levels. N2O is emitted during agricultural and industrial activities and during the combustion of fossil fuels and solid waste. N2O atmospheric levels have increased 18 percent since the beginning of industrial activities. Fluorinated gases, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic compounds emitted through industrial processes and now are being used to replace ozone-depleting compounds such as chlorofluorocarbons in insulating foams, refrigeration, and air conditioning. Although they are emitted in small quantities, these gases have the ability to trap more heat than CO2 and are considered High Global Warming Potential gases. Atmospheric concentrations of fluorinated gases have been increasing over the last two decades and are expected to continue (USEPA 2009b, 2010b). Global atmospheric greenhouse gas concentrations are a product of emissions and removal over time. Through the process of photosynthesis, atmospheric carbon is captured and stored as biomass in vegetation, especially forests. Soils also store carbon in the form of decomposing plant materials and constitute the largest carbon reservoir on land. The stored carbon can be released back into the atmosphere when biomass is burned (EIA 2010). In addition, CO2, N2O, and CH4 emissions increase in areas where soil disturbance occurs (Kessavalou et al. 1998). Models predict atmospheric concentrations