Energy-related greenhouse gas emissions declined in 2012 to their lowest level since 1994 due in large part to reduced coal use, according to an Energy Information Administration report released Friday.
Emissions have declined every year except during 2007, the report noted.
Coal is almost exclusively used to generate electricity, but as natural gas prices have fallen in recent years, it's become more cost effective to burn natural gas instead of coal. As a result, more utilities have switched over to natural gas-fired power plants, which emit less carbon dioxide overall than coal-fired plants.
But while the discovery of massive supplies of natural gas has pushed prices down to historic lows, costs are starting to rise again, making coal more competitive for electricity generation. The EIA predicts that coal will start regaining some market share in the power production business, which could have a negative impact on carbon emissions.
"The idea is that due to rising natural gas prices, we're going to continue a trend we saw in the second part of 2012, which is the very dramatic increase of natural gas in the power sector that happened in the first half of 2012, starts to abate," says Marie Rinkoski-Spangler, an analyst at the EIA.
Another reason emissions have fallen off are more efficient vehicles and less overall miles traveled, Rinkoski-Spangler says. Finally, the 2011-2012 winter was particularly mild, reducing the amount of power and fuel people used to heat their homes, and more than offsetting the uptick in power used during the warm summer months.