Climate-warming carbon emissions in the United States fell about 11% between 2007 and 2013. Some media reports have attributed much of that decline to an ongoing shift from coal toward natural gas for generating electrical power, but a new study suggests that the largest influence by far is the slump in the U.S. economy. Researchers looked at how six different factors—including population growth, shifts in consumer habits, and changes in the mix of fossil fuels used to generate electrical power, among others—affected carbon emissions trends in the United States from 1997 through 2013. Prior to 2007, rising emissions were driven by economic growth, with 71% of the rise due to increased consumption of goods and services and the remainder pinned on the nation’s population growth, the researchers say. But from 2007 to 2009, only 17% of the steep decline in emissions resulted from decreased use of coal and an increased use of natural gas and renewable sources of energy such as solar and wind power, the team reports online today in Nature Communications. The remainder stemmed from a decreased consumption of goods and services, the researchers note. From 2009 through 2013, even as the economy recovered and the U.S. population grew, carbon emissions fell slightly thanks to high gasoline prices (which stifled consumption), a mild winter in 2012 (which trimmed the demand for home heating), and more energy-efficient manufacturing. The researchers propose, however, that that transient combination of factors likely won’t prevent carbon emissions from rising substantially once the U.S. economy kicks into a higher gear.
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