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Methane Complicates U.S. Greenhouse Emissions Outlook

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The decline of the use of coal as the primary source of fuel for power plants across the nation is behind a drop in U.S. greenhouse gas emissions in 2012, the U.S. Environmental Protection Agency announced Wednesday.

But while both the EPA and the U.S. Energy Information Administration have announced that overall carbon dioxide and greenhouse gas emissions declined nationwide in 2012, hidden in the data is that some states, particularly those producing shale oil and gas, are seeing some increases in methane emissions, the most potent greenhouse gas.

Credit: U.S. Environmental Protection Agency

U.S. greenhouse gas emissions, including carbon dioxide, methane and other pollutants, dropped 4.5 percent from 2011 to 2012, according to the EPA’s data, which echoed an EIA report issued Monday showing a 3.8 percent decline in energy-related carbon dioxide emissions between 2011 and 2012.

The EPA’s 2-year-old Greenhouse Gas Reporting Program collects annual emissions data from about 8,000 industrial pollutant-emitting facilities nationwide. Since 2010, the program’s data have shown that GHG emissions from power plants have decreased 10 percent because natural gas is competing with coal as the nation’s primary fuel for electricity generation.

Responsible for releasing more than 2 billion metric tons of greenhouse gases into the atmosphere in 2012, power plants of all kinds were by far the largest emitters of greenhouse gases. Petroleum and natural gas systems, including oil and gas production and distribution, were the second largest emitters, sending 217 million metric tons of greenhouse gases into the air.

Looking at the EPA’s methane emissions data alone paints a more complicated picture, however. Nationwide methane emissions dropped only slightly from 193 million metric tons in 2011 to 192 million metric tons in 2012, and many major oil and gas-producing states are seeing their methane emissions increase.

Leaks in the oil and gas drilling, production and distribution process are suspected to be a major source of methane emissions. However a study published in September and led by University of Texas chemical engineering professor David T. Allen found that methane emissions from some natural gas production sites were less common than expected, or in line with previous EPA estimates.

Texas, home to several major shale oil and gas plays and by far the nation’s biggest industrial air polluter, saw its methane emissions increase from 12.96 million tons to 13.41 million tons between 2011 and 2012.

Colorado, home to rapid oil and gas development northeast of Denver, saw both its overall greenhouse gas and methane emissions decline during that time, but methane emissions from the oil and gas sector shot up from 499,680 metric tons in 2011 to 735,630 metric tons in 2012.

Shale oil-rich North Dakota saw both its overall GHG and methane emissions rise last year, while shale gas-rich Pennsylvania saw an overall drop in its GHG emissions but a rise in methane emissions in the oil and gas sector.

Bucking the trend, Wyoming, a major producer of coal, oil and gas, saw its methane emissions decline while overall GHG emissions rose in 2012.

Every state is responsible for some share of the nation’s greenhouse gas emissions, but Texas emitted more greenhouse gases overall than the second and third most-polluting states combined last year.

Texas alone was responsible for 393 million metric tons of greenhouse gas emissions, mostly from power plants, refineries and the chemical industry — more than three times the carbon footprint of California, which emitted only 114.6 million metric tons. Other states in the top five biggest GHG emitters were Indiana, with 154.6 million metric tons of GHG emissions, Pennsylvania with 142.7 million tons, Louisiana with 140.4 million metric tons and Ohio with 133.3 million metric tons.

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