The analysis clarifies the role of methane releases in the
calculation of comparative emissions between the two fossil fuels
and explores how the growing share of natural gas production from
shale formations could change that fuel’s footprint.

 

Earlier this year, the U.S. Environmental Protection Agency (EPA)
updated its methodology for estimating methane emissions from
natural gas systems, generating concern that the new, higher
methane figures could minimize the greenhouse gas advantage that
natural gas is seen widely to have over coal.

 

Applying the EPA’s new estimates, the life-cycle greenhouse gas
footprint of natural gas-fired electricity increased roughly 11
percent, according to the study.

“Despite a substantial increase in the methane assumed to be
emitted during natural gas production, we found that U.S. natural
gas-fired electricity generation still released 47 percent fewer
greenhouse gases than coal from source to use,” said Saya Kitasei,
a Worldwatch Institute Sustainable Energy Fellow and one of the
contributing writers.

 

The authors stress that although methane emitted during natural gas
production might not make natural gas-fired electricity dirtier
than coal, it can and must be mitigated immediately. “In addition
to being a potent greenhouse gas, methane is a valuable energy
source that natural gas producers should be capturing for sale,”
said Kitasei.

“Because some of the same technologies that prevent methane from
entering the atmosphere also reduce emissions of smog-forming
compounds, tackling methane emissions is a win-win-win
proposition.”

 

The study points out that regulatory and technological tools to
reduce methane emissions are being demonstrated in some U.S. states
and by some companies.

Although reducing methane emissions has been largely voluntary
to date in the United States, new EPA rules could require the
natural gas industry to measure and report its greenhouse gas
emissions and to use control technologies that will significantly
reduce associated methane emissions as early as 2012.

 

Further highlights from the study:

• The EPA’s recent upward revisions of methane emissions
from natural gas are related largely to the production share of the
gas value chain, especially during the unloading of liquids and (in
the case of hydraulically fractured wells) during flowback.

• The life-cycle greenhouse gas footprint of natural gas is
lower than coal under all “global warming potentials” tested, with
the smallest difference calculated using a GWP of 105, where the
emissions are 27 percent less than those of coal-fired
generation.

• Methane emissions during natural gas production,
processing, transport, storage, and distribution can be mitigated
now at moderately low cost using existing technologies and best
practices. Such capture potential presents a commercial and
investment opportunity that would further improve the life-cycle
greenhouse gas