Greenhouse Gas Emissions Fall in U.S.

In 2011, domestic carbon dioxide emissions shrank while economic activity increased for the first time in a decade. Growing use of natural gas-burning power plants (pictured) over coal-fired plants factored into the decrease.

American carbon dioxide emissions fell to a 20-year low in 2011, as the economy shed 9 percent of its energy-related emissions output since 2005, according to the U.S. Department of Energy.

After a 3.3 percent increase in energy-related carbon dioxide (CO2) emissions in 2010, output fell by 2.4 percent in 2011, or 136 million metric tons. Emissions have declined for four out of the last six years, according to the U.S. Energy Information Administration's August 14 report.

Several factors aided the decline. Gasoline prices increased 27 percent from 2010 to 2011, from $2.78 to $3.53 per gallon, which led to an estimated 1.2 percent decline in vehicle miles traveled nationwide. Vehicle fuel efficiency also improved, combining with the price increase to cut gasoline consumption about 3 percent overall. Also, power plants that burn coal are being replaced in favor of natural gas, which is growing as a cost-effective, clean-burning alternative to coal.

Emission levels have been pegged to changes in gross domestic product (GDP) in recent years; when GDP fell in the recession years of 2008 and 2009, emissions also declined, and both increased in 2010. In contrast, the emissions decrease of 2.4 percent in 2011 was coupled with a 1.8 percent increase in GDP.

Economic growth has significantly outpaced emissions increases since 1990 – GDP has increased by 66 percent in that time, but emissions have only gained 9 percent.

The 526 million tons of emissions cut since 2005 is comparable to the annual output of some developed countries; in 2008, Canada's emissions were estimated at just over 544 million tons.