What’s the largest source of methane emissions in the United States?

From reading newspapers and magazines or listening to political figures in Washington, you’d probably guess it’s the natural gas industry.

And you’d be wrong.

According to the Environmental Protection Agency’s new Greenhouse Gas Inventory, the largest anthropogenic source of CH4 emissions in the United States is “enteric fermentation.”

In other words, cows.

It turns out that cow flatulence, which accounts for more than a quarter of U.S. methane emissions, was the No. 1 source in 2013, just ahead of emissions from natural gas systems.

According to the EPA, these emissions are tied roughly to the size of the nation’s cattle population.

I mention it here just to give some perspective, since few others will.

Indeed, the perception seems to be that it is only our industry that produces methane emissions. That was the widespread impression in the media after the Obama administration in January announced plans to regulate methane emissions from our industry.

The misperception continued last week when the EPA’s latest emissions inventory came out. Scientific American published a slightly misleading piece from the news service ClimateWire titled, “Methane Leaks from Oil and Gas Wells Now Top Polluters.”

The claim in the headline is correct, but only technically. If you add the relatively small methane emissions from petroleum systems to those from natural gas, then the figure does eclipse those from cows.

However, it’s misleading because oil and gas are two separate categories, while enteric fermentation is one.

If it makes sense to lump oil and natural gas together – and I am not saying it doesn’t – then you should also add the much larger emissions from another official EPA category – “manure management” – to the enteric fermentation tally.

Viewed that way, it’s clear that agriculture contributes a much bigger share of methane emissions than oil and gas. Agriculture then is the largest source of U.S. methane emissions.

The headline in Scientific American is incorrect in another way as the authors try to blame oil and natural gas wells for emissions. The EPA’s inventory looks at the entire U.S. system of producing and distributing oil and natural gas, which, in addition to wells, includes hundreds of thousands of miles of transmission and distribution pipelines as well as various processing plants and storage facilities.

This analysis reveals just how effective the industry has been in reducing emissions. Since 1990, methane emissions from agriculture have increased by 14 percent, while methane emissions from oil and natural gas systems have fallen by 14 percent despite massive increases in domestic oil and gas production. In fact, emissions from agriculture are now 20 percent higher than from oil and natural gas.

So what’s the point?

We’re not calling for a crackdown on cows. We just hope to inject some perspective and understanding into the public debate about the challenges we face. This is especially important when policymakers are looking to load up our industry with regulations despite the obvious success we have had in finding ways to lower emissions.