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New Information on Methane Emissions

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“Emissions of the greenhouse gas methane due to human activity were roughly 1.5 times greater in the United States in the middle of the last decade than prevailing estimates,” said a story in the New York Times in late November. Perhaps you saw it.

The story was based on a study by Scott Miller and 14 others. Instead of measuring methane emissions from the bottom-up (going source by source, trying to figure out how much methane is emitted by each, and summing them into a total), they measured methane levels in the atmosphere, and worked backward to figure out how much was being emitted (a top-down approach).

That methane emissions should be 1.5 times higher than estimated sounds rather dire, as methane’s global warming potential is about 23 times greater than carbon dioxide’s.

However, a blog post on Real Climate may put it in context. The blog notes that methane is well mixed in the atmosphere, and global concentrations of methane are not rising rapidly. The United States emits only about 5% of world methane emissions, so the effect of the changed estimate would be real, but not drastic.

I don’t usually use posts in blogs as sources of material, no matter how reputable the blog is. There is generally no way to ensure that the content of the post has been subjected to peer review and, thus, represents accepted scientific thinking. However, so many media sources hype the drama that when I saw this rather calming blog post, I wanted to share it. Keep in mind that it has not been peer reviewed.

Readers who want to follow what climate scientists have to say about climate change might find the RealClimate Blog interesting.

The National Research Council has just issued a report assessing abrupt impacts of climate change. These are the sudden events that evoke such fear, like the so-called arctic methane bomb, or reversal of the Gulf Stream ocean current. I’ll report on it once I’ve had a chance to read it.

Sources:

Wines, Michael. 2013. “Emissions of Methane in U.S. Exceed Estimates, Study Finds.” New York Times, 11/25/2013.

Miller, Scot, Steven Wofsy, Anna Michalak, Eric Kort, Arlyn Andrews, Sebastien Biraud, Edward Dlugokencky, Janusz Eluszkiewics, Marc Fisher, Greet Janssens-Maenhout, Ben Miller, John Biller, Stephen Motzka, Thomas Nehrkorn and Colm Sweeney. 2013. “Anthropogenic Emissions of Methane in the United States.” proceedings of the National Academy of Sciences of the United States of America, 10.1073/pnas.1314392110. http://www.pnas.org/content/early/2013/11/20/1314392110.

“Arctic and American Methane in Context.” 2013. RealClimate. http://www.realclimate.org/index.php/archives/2013/11/arctic-and-american-methane-in-context.

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