Durée de lecture : 4 minutes7 novembre 2012 / Hervé Kempf (Le Monde)
The United States is beginning to control emissions of greenhouse gases linked to the exploitation of shale gas.
The Environmental Protection Agency (EPA) requires implementation of the first rules as of Oct 15 : operators will now flare the volatile organic compounds generated by the exploitation of shale gas. Starting in January 2015, they will capture the gas for reuse.
For the scientist who first showed the importance of these emissions, Robert
Howarth, the new regulation represents progress. In his office close to Cornell
University in Ithaca, 300 km from New York , however, he explains that it is
On the one hand, the new rules apply only to gas wells, though leakage also
occurs along transmission and distribution routes. On the other hand, Howarth
doubts the ability of the administration to control tens of thousands of wells in the
"Of course, companies will send reports certifying compliance with the rules”, he
said,"but I’m sceptical. I was an expert with a tribe in Alaska in the 1990s about
offshore oil development. It was demonstrated that oil companies sent false
information to EPA. If there is not a serious control, it does not solve the
Mr. Howarth published in the journal Climatic Change, in April 2011, with Renee
Santoro and Anthony Ingraffea, the first study showing that the exploitation of
shale gas resulted in very large emissions of methane, a powerful greenhouse
This article struck a blow, while the shale gas industry was - and remains –
in an accelerated phase of development in the United States. Since then, the
researchers’ estimate has been confirmed by other studies, such as a team from
the University of Colorado, published in the Journal of Geophysical Research in
February (Petron et al.).
At 60 years old, Robert Howarth is a respected biogeochemist who has spent his
career at Cornell University, where he is one of the eminent professors. He has
also participated in or chaired several committees of the National Academy
of Sciences on climate change and biofuels.
The researcher explains that methane leaks during drilling. "A portion of the
water used to stimulate the rock in this phase of the work returns over two to
three weeks, and carries with it the gas, which escapes into the atmosphere."
But, the long-range transport and distribution of gas are also sources of
leaks. Conventional natural gas, which uses a large part of these distribution
networks, is also a significant source of methane emissions.
"Many pipelines are old - up to a century - and poorly sealed. There is therefore
several explosions in the network annually, sometimes fatal ones as in
September 2010 in San Bruno, close to San Francisco."
A study by researchers
at Boston University should soon allow better assessment of network
emissions. Leaks also occur from gas storage stations : gas is mostly consumed
during the winter, and must be stored during the summer.
"In total, integrating all these phases,” summarized Robert Howarth, “an
estimated 3.6 and 7.9% of gas extracted during shale gas production escape.
Research conducted since confirm this magnitude."
Proponents of shale gas
argue that, by replacing coal in power plants, shale gas reduces greenhouse gas
emissions. It’s a false claim, according to the researcher, if we take into account
the full life-cycle emissions.
Another key issue in assessing the impact of the leaks on climate change is to
consider the time period when methane is the most active. Based on the work of
the 1990s, the majority of reference documents that evaluate the global warming
factor of methane are based on an atmospheric residence time equivalent to that
of carbon dioxide, which is a hundred years.
But, because methane disperses
rapidly - in ten to twenty years - its climate impact is very strong in the first two
decades after emission. It is therefore necessary to adopt other warming
OTHER FACTORS WARMING
"This is what we have done, by adopting the method used by the IPCC in its
2007 report" says Howarth. Effects on the release of greenhouse gas emissions
in the United States : "Using the old emission factors, it can be said that
the gas industry emissions make up 3% to 4% of national emissions. Using the
integrated time period of 20 years for methane, we see that the natural gas
industry accounts for 19% of emissions. This is a huge difference."
For the scientist, the global statistics on emissions of greenhouse gases must be
reviewed. "They are inaccurate. Unquestionably they underestimate methane
But, Mr. Howarth is the first to say that the debate is not over. "There
are still a lot of studies to be conducted. This is a new technology ; it has a lot of
unknowns. We must work to better assess the importance of these issues."
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Source : Translated from French
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