US CO2 Emissions down due to Natural Gas. GHG Emissions? Not so fast!

Let the celebrations begin!!

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 that cheap and plentiful natural gas has led many power plant operators to switch from dirtier-burning coal

via Associated Press.

Coal is evil, for many reasons, natural gas is less evil, but don’t tout its climate benefits, it has none.

While natural gas is a much cleaner burning fuel, and its mining is less harmful than coal’s, there’s a big variable that doesn’t get discussed very often in the media, its leakage during mining, processing and transport. Methane is 25 times more potent (pdf) than CO2 as a greenhouse gas. So, it would seem that knowing how much escapes into the atmosphere would be a fairly important variable.

It is very easy to estimate CO2 emissions from burning natural gas, it is much more difficult to measure fugitive and diffuse emissions from natural gas, fracking or otherwise. After all, the emissions occur at industrial sites controlled by drilling companies who have no interest in releasing that data. Also, it is site, and technique dependent. A conscientious driller may be able to avoid most leaks, but where’s the motivation? Natural gas is very abundant, and the price it is selling at demands high volume production and low margins. No need to plug the leaks, just the whole thing flow.

The scientific community and environmental community is well aware that comparing natural gas and coal is not as simple as looking at CO2 emissions.  Methane and CO2 also have different lifetimes in the atmosphere, with methane being shorter lived, but forcing more intensely. The short-term and long term prognoses are therefore very different. Three separate papers (see references) have looked at this issue and concluded that natural gas is no panacea.  Alvarez et al still espouses natural gas as a bridge fuel, but Howarth et al and Wigley are less optimistic.

Here’s a nice image from Wigley’s paper that shows the consequences of switching from coal to natural gas once all factors are taken into account:

It’s all about Methane leakage

Note that under all scenarios, even under zero leakage, natural gas use actually causes an increase in short-medium term climate forcing. Why? Dirty burning coal also puts out enough sulphur dioxide into the atmosphere to create fine particles that reflect incoming sunlight and cancel out some warming. It takes until 2050 at least for climate forcing from natural gas to start showing benefits over coal. Even then, the benefits are not sufficient to fight climate change. Wigley estimates that the change is 0.1°C “out to at least 2100”, big whoop.

So, what exactly might the leakage rate be? Industry and the US Environmental Protection Agency estimate it at 2% or less. When Pétron et al. went around measuring it around Denver, they measured it at 4%, with pretty high uncertainty, which makes natural gas fairly useless for fighting climate change.

It is troubling that people treat this transition to natural gas so cavalierly. One doesn’t even need to look at all the problems arising from fracking for natural gas use to be no panacea. There is some evidence that natural gas investment is also driving out wind and solar energy investment. Here in BC, our wonderful Premier Christy Clark declared that natural gas was clean energy as far as the government’s policy framework was concerned. The opposition, and government-in-waiting NDP also thinks natural gas is clean. This is disturbing, and very shortsighted.

What I say is not new, Joe Romm put it well “Natural Gas is a bridge to nowhere“, unless a very high carbon price is established (I don’t see one today, do you?).


  1. Howarth, Robert W., Renee Santoro, and Anthony Ingraffea. “Methane and the Greenhouse-gas Footprint of Natural Gas from Shale Formations.” Climatic Change 106, no. 4 (April 12, 2011): 679–690.
  2. Wigley, Tom. “Coal to Gas: The Influence of Methane Leakage.” Climatic Change 108, no. 3 (2011): 601–608.
  3. Alvarez, Ramón A., Stephen W. Pacala, James J. Winebrake, William L. Chameides, and Steven P. Hamburg. “Greater Focus Needed on Methane Leakage from Natural Gas Infrastructure.” Proceedings of the National Academy of Sciences (April 9, 2012).
  4. Pétron, Gabrielle, Gregory Frost, Benjamin R. Miller, Adam I. Hirsch, Stephen A. Montzka, Anna Karion, Michael Trainer, et al. “Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study.” Journal of Geophysical Research 117, no. D4 (February 21, 2012): D04304.

Bridge to Nowhere featured image courtesy GarlandCannon Flickr Photostream used under a Creative Commons Licence.

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