Since 1990, U.S. greenhouse gas emissions have increased by 15.8 percent, for an average annual increase of 1.1 percent. The EIA attributes the large growth in 2004 to a surging U.S. economy, which in turn resulted in more energy use.
The economy grew 4.4 percent in 2004—the fastest since 1999—and in turn the carbon dioxide generated from energy use increased by 1.7 percent. But since the greenhouse emissions grew slower than the economy, the U.S. greenhouse gas intensity—the amount of greenhouse gas emissions per unit of economic output—decreased by 2.1 percent in 2004.
The other significant contributor to greenhouse gas emissions was hydrofluorocarbons (HFCs), a class of refrigerants. HFC emissions increased by 12 percent in 2004 and have increased 246 percent since 1990. The growth in HFCs is largely due to their use in place of ozone-depleting compounds such as chlorofluorocarbons (CFCs).
