FIGURE 2.5 U.S. greenhouse gas emissions by sector in 2006. Source: U.S. EPA (2008).

FIGURE 2.5 U.S. greenhouse gas emissions by sector in 2006. Source: U.S. EPA (2008).

alized countries such as the United States, the difficulty in reducing emissions will depend in large part on the lifetimes of the existing capital stock associated with the major emitting sectors. The electric sector is the largest source of manmade emissions in the United States, primarily due to the carbon dioxide emitted during the combustion of fossil fuels. The lifetime of coal-fired power plants is measured in decades. The next largest source of U. S. greenhouse gases is the transportation sector, again due to the combustion of fossil fuels. Here the lifetime of the capital stock is typically a decade or two.

Although developed countries historically have been the major emitter of greenhouse gases, developing countries are on track to overtake them in the next few years. In their case, the issue becomes one of the capital stock put in place in the future to support their industrialization process. With the huge economic growth projected for developing countries and in the absence of incentives to act otherwise, these countries will likely turn to the cheapest energy sources to fuel their growth. These fuels currently are fossil based: coal, oil, and gas. A recent study by the Energy Modeling Forum, based on eight Energy-Economy models, projected an annual growth rate of CO2 emissions globally from the burning of fossil fuels and industrial uses to be of the order of 1 to 2 percent per year over the remainder of the



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