Time to Tighten Up Oil & Gas Industry Methane Leaks to Curb Global Warming
Posted March 28, 2012
Everyone is talking about methane leaks; it’s time to do something about them.
OK, really it’s mostly only policy wonks, but there is an important link to the weird weather everyone really is talking about.
Last week I posted on the connection between heat-trapping pollution in our atmosphere and the record-breaking warmth we’ve seen this spring. It turns out that a significant amount of this global warming pollution is methane that leaks from oil and gas industry operations.
Today NRDC published a new report called Leaking Profits: How the U.S. oil & gas industry can reduce pollution, conserve resources and make money by preventing methane waste. My colleagues have posts today on the key findings of the report (here and here) and on forthcoming clean air standards that will help spur reductions in methane emissions. In this post I will focus on how the methane reductions called for in the report would contribute to reducing global warming. The answer turns out to be a lot.
There is a great deal of uncertainty about how much methane is being emitted from any given set of sources, but one thing we know for sure from direct measurements is that the amount of methane in the atmosphere has more than doubled from natural levels and that this increase contributes about 18% of the heat-trapping effect of all global warming pollution in the atmosphere. This makes methane the second largest contributor to global warming after carbon dioxide. Once emitted, methane stays in the atmosphere for an average of about 12 years—much longer than very short term global warming pollutants such as black carbon, but much shorter than carbon dioxide, nitrous oxide, and some synthetic industrial chemicals. That means that reductions in methane emissions translate relatively quickly into reductions in the rate of global warming, so a strategy of simultaneously reducing methane, black carbon, and carbon dioxide is the best way to reduce the risk of crossing climate tipping points in the short term while also avoiding catastrophic climate change in the long term.
Natural gas and oil systems are the largest source of methane pollution in the United States, accounting for 12 million metric tons of methane or 37 percent of total U.S. methane emissions according to the latest draft EPA emissions inventory. Some recent reports suggest that this number may be too low, in which case the benefits of the emissions-reducing technologies described in NRDC’s report will be even greater. (The starting point for NRDC’s report was the 2011 inventory, which was the most complete data set available when the research began. Differences between the 2011 inventory and the currently available draft 2012 inventory are minor.)
The ten technologies described in the Leaking Profits report could reduce these emissions by more than 80 percent, or by about 10 million metric tons of methane. That would erase any questions about whether switching from coal to gas to generate electricity benefits the climate. It would reduce U.S. methane emissions by about one-third—or more if the initial methane emissions from natural gas production were significantly underestimated. That’s a significant contribution to curbing global warming any way you look at it, but how does it compare to other measures, such as reducing carbon dioxide emissions from power plants or cars?
Comparing the benefits of reducing methane emissions with those of reducing carbon dioxide is not completely straightforward primarily because of the different length of time the two pollutants stay in the air after being emitted. Following an approach adopted in the Framework Convention on Climate Change, EPA uses a global warming potential index (GWP) calculated over a 100 year time horizon to put all heat-trapping gases in common units of carbon-dioxide-equivalents (CO2eq).
I discussed some of the issues related to determining GWPs here and here. The biggest issue is what time frame to consider, and as I have argued before there is no single right answer for that. But regardless of the time horizon, EPA is using an out-of-date value for methane’s GWP that does not adequately account for the chemical interactions that amplify methane’s warming effects. EPA has stuck with a value of 21, which comes from the IPCC’s 1996 report, because it is specified by the reporting guidelines adopted by the climate convention. The most recent IPCC report calculates a 100-year GWP of 25 and more recent research, which attempts to more fully account for methane’s atmospheric chemistry, suggests that a better 100-year value would be 33. Looking at shorter time frames would increase the GWP still further, to as much as 105 over a 20 year time horizon.
In a previous post I suggested that a GWP of 50 might be a reasonable middle ground. Let’s use that value again here because it makes the math easy. Reducing methane emissions by 10 million metric tons would then be equivalent to reducing carbon dioxide emissions by 500 million metric tons. That’s a lot—it’s equal to about one-quarter of the emissions from all U.S. power plants or half of the emissions from U.S. passenger cars. EPA offers a nifty calculator that provides a variety of emission equivalents: Plug in 500 million, select units of metric tons, hit calculate, and you find that this is equivalent to the annual emissions from almost 100 million cars or more than 100 coal-fired power plants. It’s also equivalent to the emissions from generating the electricity consumed annually by more than 60 million homes, or from burning over 1 billion barrels of oil. The equivalency estimates presented in the report itself are lower than this because we conservatively used a GWP of 25 to do the calculation shown there.
Yesterday EPA proposed historic pollution standards for new power plants, which would be the first national limits on industrial carbon pollution. Together with forthcoming standards addressing the existing fleet of aging power plants (which EPA is also required to issue under the Clean Air Act), EPA will be tackling the largest source of global warming pollution in the United States. EPA has already proposed breakthrough standards that will cut in half the carbon emissions from automobiles, the second largest source. The Leaking Profits report points to the next logical front in the effort to curb global warming—strong standards to require the oil and gas industry to clean up its act.
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