Category Archives: methane

“The Environmental Protection Agency has estimated the leak rate at a little more than 2 percent . . .”

J. Nocera, “How to Extract Gas Responsibly” NYT (Feb 28, 2012)

FACT: In 2010 and 2011, the EPA substantially revised and increased their estimates of methane emissions from natural gas systems.  As of the end of 2011, the most recent EPA data indicate leak rates of 2.5% for conventional natural gas and 3.9% for shale gas (details of calculation here) over the full life-cycle.  A recent field study of methane emissions from an unconventional gas field in Colorado suggests the EPA estimates may be low.

“If there is a tipping point 20 years in the future of our current trajectory, then we are going to reach it, and whether there is more or less methane in the atmosphere at that time won’t make a difference…On the other hand, if we can stabilize atmospheric concentrations of greenhouse gases below 450 ppm (CO2 equivalents on the standard 100-year timeframe measure) by 2050, and then gradually reduce them, there is a good chance of avoiding a rise of more than 2 degrees by, say 2100.”

-J. Quiggan “Timescales and timeframes” (Mar 7, 2012)

FACT: Both Shindell et al. 2012 and a report from the United Nations in 2011 argued strongly that emissions of methane and black carbon (i.e. soot) must be controlled immediately.  Without such controls, regardless of whether or not carbon dioxide is controlled, the Earth will warm to 1.5 to 2 degrees C above the long-term average background by 2030 to 2045.

At these temperatures, a major change in the planet’s climate system become increasingly likely, and there is a high risk of positive feedbacks making it extremely difficult to control global warming.

PSE_UNEPWMOFig3Fig. Observed global mean temperature from 1900 to 2009 and projected future temperature under various scenarios of controlling methane + black carbon (BC) and carbon dioxide, alone and in combination. An increase to 1.5o to 2.0 o C above the 1890-1910 baseline (illustrated by the yellow bar) poses high risk of passing a tipping point and moving the Earth into an alternate state for the climate system. Source: UNEP/WMO 2011.

See also Howarth et al. 2012 background paper for the National Climate Assessment and Hanson et al 2007.

“methane is 20 times more powerful than carbon dioxide as a greenhouse gas.”

– various sources

FACT: The best and most recent science indicates that methane is 33 times more powerful than carbon dioxide as a greenhouse gas, when considered over an integrated time period of 100 years following emission, and 105 times more powerful on an integrated 20 year time period.

The global warming potential or GWP, is a simple metric often used to assess how much more powerful a given greenhouse gas is when compared to carbon dioxide. Back in 1996, the Intergovernmental Panel on Climate Change estimated the GWP for methane as 21, considered over a 100-year time period following emission. As of 2007, the IPCC presented global warming potentials (GWP) for methane of 25 for a 100-year integrated time-frame and 72 for a 20-year integrated time frame after emission. Using a more recent model to better capture how methane interacts with other radiatively active substances, Shindell et al. in a 2009 paper in Science updated these factors to 33 and 105 respectively. These higher values reflect the best, most current science. The GWP for methane is less at the longer time scale simply because methane does not stay in the atmosphere for as long as carbon dioxide.