Last week, the Associated Press reports – under the headline “CO2 emissions in US drop to 20-year low” – that “In a surprising turnaround, the amount of carbon dioxide being released into the atmosphere in the U.S. has fallen dramatically to its lowest level in 20 years, and government officials say the biggest reason is…cheap and plentiful natural gas.”

In its report, the AP notes:

In a little-noticed technical report, the U.S. Energy Information Agency, a part of the Energy Department, said this month that total U.S. CO2 emissions for the first four months of this year fell to about 1992 levels.

That report – highlighted in this Marcellus Shale Coalition recent press release – states:

It is difficult to draw conclusions from one year of data. Just as 2009 was an atypical year in terms of the magnitude of the emissions decline, and 2010 did not signal a new trend in emissions growth, there are specific circumstances (for example, the large increase in hydropower generation) that contributed to the decline in emissions in 2011. Other factors, such as improvements in vehicle fuel efficiency, abundant supplies of natural gas, and increased use of non-hydro renewable generation, however, could play a continuing role in 2012 and subsequent years. (EIA, 8/14/12)

More from the AP:

While conservation efforts, the lagging economy and greater use of renewable energy are factors in the CO2 decline, the drop-off is due mainly to low-priced natural gas, [EIA] said.

A frenzy of shale gas drilling in the Northeast’s Marcellus Shale and in Texas, Arkansas and Louisiana has caused the wholesale price of natural gas to plummet from $7 or $8 per unit to about $3 over the past four years, making it cheaper to burn than coal for a given amount of energy produced. As a result, utilities are relying more than ever on gas-fired generating plants.

“A lot of our units are running much more gas than they ever have in the past,” said Melissa McHenry, a spokeswoman for Ohio-based American Electric Power Co. “It really is a reflection of what’s happened with shale gas.”

The [natural] gas boom “is actually one of a number of reasons for cautious optimism,” [Michael Mann, director of the Earth System Science Center at Penn State University] said.

According to recently released production data by the Pennsylvania Department of Environmental Protection, natural gas output in the commonwealth continues to increase, with 704 Bcf of gas produced over the past six months. This from the Pittsburgh Post-Gazette:

Gas production across the state climbed from January to June, with 704 billion cubic feet of gas produced, up from the 630 billion cubic feet reported from July to December 2011.

StateImpact Pennsylvania reports that “Pennsylvania’s Mar­cel­lus Shale boom is still boom­ing. …The amount of nat­ural gas taken out of the ground from Jan­u­ary to June increased by an astound­ing 61 per­cent, com­pared to the first six months of 2011.”

Be sure to visit StateImpact’s post, which includes a few graphics on the highest producing counties in the commonwealth.