Humans are responsible for as much as 40 percent more methane emissions than previously estimated, according to a new study published in the journal Nature today. Methane is a powerful greenhouse gas that can be produced biologically, seep out of the ground naturally, or bubble out of mud volcanoes. It’s also a potent byproduct of fossil fuel production.

Combined, both natural- and human-released methane emissions are responsible for about a quarter of the global warming we’re experiencing. But human-released methane makes up a much bigger slice of those emissions than people originally thought, the study’s findings suggest. They found that human-caused methane emissions might be 25 to 40 percent higher than prior estimates. Previous measurements of how much naturally occurring methane is heating up the planet were an order of magnitude too big, the researchers found.

There is an upside to all of this: the findings also imply that there’s an even bigger opportunity to rein in how much methane we release. Methane is more potent than carbon dioxide, so slashing it from our global greenhouse gas emissions can have an outsized effect. Most human-caused methane is inadvertently leaked while producing and transporting gas and oil, so improving those systems “could give us a pretty big bang for a buck,” says Andrew Rice, an associate professor at Portland State University who was not involved with the study.

“The onus is on us.”

“The onus is on us to recognize that we can, at the very least, try to get the [oil and gas] industry to quantify these in a better sense, because what I indicate is that they’re vastly under reporting it,” lead author Benjamin Hmiel tells The Verge.

To conduct this study, Hmiel and his colleagues studied ice core measurements from Greenland between 1750 to 2013 on top of previous data from Antarctica. They used the isotope carbon-14 as a sort of chemical fingerprint to determine whether the methane present in the ice core came from biological sources like cows and bacteria or emerged from underground deposits. (If it has carbon-14, it came from living things.)

Until roughly 1870, biological sources dominated the ices cores. But around that time, fossil fuel production started picking up, and researchers saw a huge jump in methane that didn’t have any carbon-14. That allowed them to estimate what was seeping out of the ground naturally in pre-industrial times and compare it to what people are currently seeing in the atmosphere. The difference is due to human activity.

Previous efforts to quantify anthropogenic methane measured emissions directly at each potential source — from seeps to oil wells. The difficulty in doing that is one reason why the study’s findings are “actually not that surprising,” according to Eric Kort, an associate professor at the University of Michigan who was not involved in the study. Methane emissions from oil, gas, and coal activities tend to systematically be underestimated, he says, in part because they often use averages for emissions and don’t take into account hardware failures or other errors that lead to unintentional leaks.

“a really Herculean effort”

Hmiel’s approach to measuring methane emissions is “a really Herculean effort that involves — no joke — each sample is about 1000 kilograms of ice that we have to melt,” he says. But it does come with one large limitation: nuclear bombs and reactors put more carbon-14 in the atmosphere, messing with the study’s reading of carbon-14 in methane in samples from 1945 or later (after the first nuclear bombs were deployed). For those later samples, the study authors had to use computer models to make the rest of their estimates of human-caused methane.

So while this study offers a promising new way of understanding humanity’s impact on the climate through methane, “it will require additional modeling, to verify if this is going to fly, basically,” Rice says.