Greenhouse gas emissions in the United States dropped by 3.4% in 2012, federal environmental regulators reported Tuesday.
The decline over the previous year was driven mostly by power plant operators switching from coal to natural gas, improvements in fuel efficiency for transportation and a warmer winter that cut demand for heating, according to an inventory released by the U.S. Environmental Protection Agency.
The analysis shows the nation released the equivalent of 6,526 million metric tons of carbon dioxide in 2012, the lowest level since 1994.
The annual inventory tracks emissions of planet-warming gases across all sectors, including electricity generation, transportation, industry and agriculture. It also calculates the amount of carbon dioxide removed from the atmosphere by natural "sinks" such as trees and soil.
About 82% of the nation's greenhouse emissions in 2012 were carbon dioxide, the main pollutant causing climate change. The inventory also accounts for other heat-trapping gases, such as methane and nitrous oxide.
Total greenhouse gas emissions in the U.S. were on the rise until about 2007, when they started to trend downward, the report shows.
The EPA inventory is a national overview of greenhouse gas emissions going back to 1990. The data is reported to the United Nations Framework Convention on Climate Change.
A January report by the U.S. Department of Energy found that carbon dioxide emissions in the nation's energy sector rose about 2% in 2013 after years of decline. The report attributed the uptick to power plants bucking the trend toward natural gas and burning more coal to generate electricity last year.