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47 Chapter Five: Coal and the Environment

Greenhouse Gas Almost any kind of burning produces carbon dioxide. It is called a greenhouse gas because, in the atmosphere, it helps to trap and hold heat—much like the panes of glass in a greenhouse. Along with other greenhouse gases, such as methane, carbon dioxide is causing the surface temperature of the Earth to rise, a phenomenon termed global warming. Nearly all scientists now agree that global warming is here, that it is increasing, that it is caused by human activities—chiefly, burning fossil fuels. In North America, carbon dioxide accounts for about four-fifths of all greenhouse gas emissions. About one-third of this carbon dioxide comes from electricity generation, and coal creates around two-fifths of these emissions. Taking into account other coal uses, coal is responsible for broadly 30 to 35 percent of US greenhouse gas emissions. (Similar calculations show that petroleum oil is the source of up to 40 percent of US greenhouse gas emissions.) Methane constitutes around one-tenth of North America’s greenhouse gas emissions. Methane is very powerful—it is more than 20 times more effective at trapping heat than carbon dioxide over a time span of 100 years. However, methane does not last in the atmosphere as long as carbon dioxide does. So its greenhouse effects are bigger over a short period, while carbon dioxide’s are not as big but last longer, since it persists for 100 to 200 years. Low-level methane seeping from surface

A Warmer Earth Global warming is predicted not only to make the Earth’s air, land, and water hotter, but also to change patterns of weather, create more storms and other extreme events, bring droughts and floods to new regions, and warm the oceans, which will kill corals and marine life. It will melt glaciers and ice caps to raise the sea level and flood vast low-lying areas. And there are probably many more, as yet unknown, effects of global warming.