In a report released on Friday the federal agency said CO2 emissions in 2012 were 5.3 billion metric tons and, with the exception of 2010, emissions had been on a downward trend every year since 2007.

What is more, the largest emissions drop last year stemmed from coal.

“During 2012, particularly in the [northern] spring and early summer, low natural gas prices led to competition between natural gas and coal-fired electric power generators,” the EIA said.

“Lower natural gas prices resulted in reduced levels of coal generation and increased natural gas generation – a less carbon-intensive fuel for power generation, which shifted power generation from the most carbon-intensive fossil fuel [coal] to the least carbon-intensive fossil fuel [natural gas].”

The agency noted that other contributory factors included a decreased demand for transportation fuels and mild winter temperatures that resulted in a drop in heating demand.

A warmer-than-normal winter, particularly during the first quarter of last year, was enough to more than offset a nominal increase in cooling degree days during the summer season.

“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 [starting] to abate,” EIA analyst Marie Rinkoski-Spangler told US News and World Report.

EIA said it would publish a full analysis of 2012 energy-related CO2 emissions later this year.

While the reduced demand for coal over 2012 had its impact on the industry and production, the tide seems to be changing as historically low natural gas prices begin to rise.

It is making coal a more competitive choice for generation once again.

How that change will impact emissions, of course, remains to be seen.