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New study finds US anthropogenic methane emissions 1.5 times higher than previously estimated by EPA

Using a new methodology, a study published in Proceedings of the National Academy of Sciences (PNAS) has concluded that anthropogenic emissions of methane from agriculture and fossil fuel extraction and processing (i.e., oil and/or natural gas) are likely significantly greater than cited in existing studies.

The researchers quantitatively estimated the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial datasets, and a high-resolution atmospheric transport model.

The authors are from Harvard University; Carnegie Institution for Science; University of Michigan; National Oceanic and Atmospheric Administration; Lawrence Berkeley National Laboratory; Atmospheric and Environmental Research; European Commission Joint Research Centre; and University of Colorado Boulder.

Results indicated that emissions due to ruminants and manure are up to twice the magnitude of existing inventories, and that regional methane emissions due to fossil fuel extraction and processing could be 4.9 ± 2.6 times larger than in EDGAR, the most comprehensive global methane inventory.

… the discrepancy in methane source estimates is particularly pronounced in the south-central United States, where we find total emissions are ∼2.7 times greater than in most inventories and account for 24 ± 3% of national emissions. The spatial patterns of our emission fluxes and observed methane–propane correlations indicate that fossil fuel extraction and refining are major contributors (45 ± 13%) in the south-central United States.

… These results cast doubt on the US EPA’s recent decision to downscale its estimate of national natural gas emissions by 25–30%. Overall, we conclude that methane emissions associated with both the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories.

—Miller et al.

Overall, results show that current inventories from the US Environmental Protection Agency (EPA) and the Emissions Database for Global Atmospheric Research underestimate US methane emissions nationally by a factor of ∼1.5 and ∼1.7, respectively.

The difference lies in the methodology. The EPA and EDGAR use a bottom-up approach, calculating total emissions based on emissions factors—the amount of methane typically released per cow or per unit of coal or natural gas sold, for example. The new study takes a top-down approach, measuring what is actually present in the atmosphere and then using meteorological data and statistical analysis to trace it back to regional sources.

Resources

  • Scot M. Miller, Steven C. Wofsy, Anna M. Michalak, Eric A. Kort, Arlyn E. Andrews, Sebastien C. Biraud, Edward J. Dlugokencky, Janusz Eluszkiewicz, Marc L. Fischer, Greet Janssens-Maenhout, Ben R. Miller, John B. Miller, Stephen A. Montzka, Thomas Nehrkorn, and Colm Sweeney (2013) “Anthropogenic emissions of methane in the United States” PNAS 2013 doi: 10.1073/pnas.1314392110

Comments

mahonj

It sounds like they really need to nail this one.

They need to find the sources of the ch4 and measure them directly.

Then they need to legislate to reduce the leaks.

If we take 3 sources: fracking, belching cows and landfill, we can see that it should be possible to solve fracking and landfill; the cows will be a bigger problem (lots of farmers, lots of votes).

If the cows are in a shed, it might be possible to vent the methane through some kind of oxidizing agent and burn it off (I am not a chemist, so I am guessing here). If the cows are in a field, this won't be possible.

You should be able to put a membrane over landfill (when it's full?), collect the gas and flare it off (using it would be better, but there might not be enough to make it worthwhile.

Ditto for fracking.

This (and soot) needs to be addressed ASAP, as it may be possible to make more progress, faster, than trying to reduce CO2 emissions which are a natural product of combustion, and hard (expensive) to reduce.

Engineer-Poet

Some methane from landfills is purfied and used as fuel; there are even commercial producers selling systems for that purpose.

Methane is a pure loss to a cow, and likely to its bacteria as well.  It may well be possible to slash the methane emissions by feeding them differently.

ai_vin

Indeed, methane IS a significant loss of feed energy, and that increases feed costs so farmers have a profit motive to find ways to reduce it. In fact because the feed conversion ratio (FCR), feed conversion rate, or feed conversion efficiency (FCE) is so important in animal husbandry there are research programs going on all over the world.

Here in Canada Agriculture and Agri-Food Canada (AAFC) scientists at the Lethbridge Research Centre in Alberta have found "several feeding strategies show promise. For example, increasing the level of dietary fat by feeding a diet of crushed oilseeds (sunflower seed, canola seed or flaxseed) or dried corn distillers grain reduced the energy lost as methane by up to twenty percent. Similar reductions in methane were also seen when other fat sources, such as whole cottonseed, plant oils, and some ethanol byproducts were added to the diet. Overall methane was lowered by 5 percentage units for each percentage of crude fat added to the dietary dry matter."

There's also the idea of selective breeding animals for increased feed conversion efficiency.

BTW, it's not just cows. Sheep, et al also are methane producers - but of course some animals have higher feed conversion efficiency than others. So we could decrease farm methane production by changing OUR diet as well.

dursun

Cows do not create CH4 out of nowhere. They just recycle the carbon that already exist in biosphere.

Engineer-Poet

Converting atmospheric CO2 into methane emissions has a substantial greenhouse effect.

ai_vin

dursun, according to the scientists, a methane emission will have 25 times the effect on temperature of a carbon dioxide emission of the same mass over the following 100 years. And they also say that this figure probably represent an underestimate.

HarveyD

Relying on producers to establish or report CO2, CH4 and other emissions will always lead to false data.

In may be appropriate to multiply the emissions reported by 2 or 3 until such time as full proof monitors are installed.

Larzen

Good thing those farting dinosaurs died off.

Larzen

Can't wait for Lab Meat.

Arnold

The figures are definitely rubbery.It may have shorter life cycle from 10 to 25 or 50 years before converting to CO2.
Aircraft emissions similarly are poorly explained with 2X affect stated but less understanding of the time frame.
Deer, goat horses are much lower emission.
Diet and relevant genomes including microbial are affecting.

HarveyD

Horse, goat and bison meat production may be more effective and produce less pollution than beef?

Double/triple burgers with less fat and less pollution could sell for an extra 30% or so and become a great business success?

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