Current GHG Emissions Picture
Climate-friendly Energy Policy: Options for the Near Term
Current Greenhouse Gas Emissions Picture
Greenhouse gas emissions from U.S. energy use and production are primarily CO2 emissions from the combustion of fossil fuels in the electricity generation, buildings, industrial processes, and transportation sectors.18 (See Figure 3.) CO2 from fossil fuel combustion accounts for 82 percent of total U.S. GHG emissions.19 Figure 4 shows U.S. CO2 emissions broken down by fuel source.
One way to view the broad relationship between energy use and CO2 missions is to examine shifts in two indices: energy intensity (measured by energy used per dollar of gross domestic product (GDP) created) and carbon intensity (measured by CO2 emissions per dollar of GDP created). The first value indicates the economy’s overall energy efficiency, while the second is a function of the fuel mix and generation technologies used to meet the nation’s energy needs. With regard to fuel mix, it is important to understand that different types of fossil fuels have different levels of carbon content. (See Figure 5.) Both energy intensity and carbon intensity are influenced by energy policy choices.
As the U.S. economy has grown, CO2 emissions have increased, although at a slower rate than conventional measures of economic output. During the 1990s, the divergence between CO2 and GDP growth was primarily a result of lower energy intensity. From 1990 to 2001, GDP grew by about 2.9 percent per year, while CO2 from energy grew by about 1.3 percent per year, i.e., CO2 grew at about half the rate of GDP. Energy use per dollar of GDP fell by 1.7 percent per year, while CO2 emissions per unit of energy consumed have remained at roughly the 1990 level.20 This decrease in the U.S. economy’s energy intensity since the early 1990s has resulted in large part from an increase in non-energy-intensive economic sectors (e.g., computer equipment and semiconductor manufacturing) relative to traditional energy-intensive manufacturing industries (e.g., steelmaking), as well as from energy efficiency improvements.21
The primary CO2 growth components during the 1990s were electricity generation and transportation. CO2 emissions from the electric power sector grew by 24 percent between 1990 and 2001, and CO2 emissions from transportation increased 19 percent during this period.22 The demand for electricity has grown with the U.S. economy and with substantial increases in the market penetration of electricity-consuming electronic equipment, consumer appliances, and manufacturing technologies. In the transportation sector, an increasing proportion of vehicles on the road (e.g., minivans, sport utility vehicles, and light trucks) are not subject to the passenger car Corporate Average Fuel Economy (CAFE) standards, but instead are subject to the significantly less stringent “light-duty truck” CAFE standards. CAFE standards established in 1975 required new passenger car fuel economy to reach 27.5 mpg in 1985, where the standard remains today. Less was required of light trucks; standards set by the U.S. Department of Transportation increased to 20.5 mpg in 1987 and stand at 20.7 mpg today.23 The actual fuel economy of new passenger cars and light trucks has closely followed the standards, and has not increased since 1988; indeed, today’s combined fleet of passenger cars and light trucks gets fewer mpg than the vehicles sold fifteen years ago because of the growth in the proportion of light trucks in the fleet.24 Finally, all vehicles are being driven more miles as a result of relatively low gasoline prices and land-use patterns characterized by sprawl.