Animal farts and poop are major contributors to global warming. It turns out we might have been underestimating just how much.
New research finds that previous estimates of methane emissions from livestock were off by as much as 10%. The new calculations take into account changes in the ways people are using and keeping livestock.
Methane is a natural byproduct of digestion, made by that microbes in an animal’s gut that breakdown and ferment the food we eat. A gas, methane is a principle component of farts, though it’s not the one that makes them smell—sulfur-containing molecules are the biggest culprit there.
Farts are funny. Global warming is not. Unfortunately, methane is a big contributor to the greenhouse effect, helping to trap heat within Earth’s atmosphere and contributing to climate change. Carbon dioxide usually gets the blame for global warming, but methane is about 85 times more powerful when it comes to trapping heat, although it breaks down faster than carbon dioxide.
Now, a new calculation of methane produced by cows, swine and other livestock shows we may have underestimated their inputs. Researchers from the U.S. Department of Agriculture, the Joint Global Change Research Institute and the U.S. Department of Energy say the previous figures, which served as a basis for the 2006 Intergovernmental Panel on Climate Change, were off by 11%.
Their NASA-funded study appeared today in the journal Carbon Balance and Management.
Led by USDA plant physiologist Julie Wolf, the group looked at the data underpinning the IPCC’s estimate. They realized that some of it dated back decades, meaning it didn’t take into account changes in land and animal use.
“In many regions of the world, livestock numbers are changing, and breeding has resulted in larger animals with higher intakes of food. This, along with changes in livestock management, can lead to higher methane emissions,” said Wolf, according to a press release.
When they applied more recent data—like the fact that many fewer cattle in the U.S. are being used to pull farm equipment, or that manure is now more likely to be stored in huge open pits than spread on fields—they calculated that livestock in 2011 were responsible for roughly 120 million million grams of methane.
Much of that increase comes from changes in how cow poop and other manure is handled. Compared to spreading manure on fields as fertilizer, storing manure in pits encourage bacteria that produce twice as much methane. Wolf’s group calculated a nearly 37% increase in global methane emissions due to those changes. In the U.S., the increase was 71%. California is a big offender in that category. Fart methane, on the other hand, was up 8% from the IPCC’s 2006 estimate.
Livestock are not the biggest source of methane, which also comes from natural sources like wetlands, the oceans and even termites. Wolf and her colleagues estimated that livestock originated about one-fifth of methane emissions from 2003 to 2011. But they were responsible for between half and three-quarters of the increase in methane emissions seen over that time period.