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How much methane do human activities put in the atmosphere?

Humans emit roughly 400 million metric tons of methane a year: as much as two-thirds of all methane entering our atmosphere.

December 3, 2024

Methane—or CH₄—is a greenhouse gas: it traps the sun’s energy and keeps it from radiating back into space, warming the Earth. And though methane sticks around in the atmosphere for only about seven to 12 years,¹ it is a potent atmospheric warmer during that time. In the first 20 years after it enters our atmosphere, methane will trap around 84 times more heat, pound for pound, than carbon dioxide (CO₂), the best-known greenhouse gas.²

Having methane in our atmosphere is not inherently a problem. Natural processes have always released methane, contributing to the blanket of greenhouse gases that keeps our planet warm. When plants decompose underwater, for example, they can create methane. When animals like cows and sheep digest food, they release methane as they burp. But over the past 150 years, human activities have led to a huge spike in methane emissions. People extract oil, gas and coal, raise cattle for meat and dairy, and leave food waste to rot in landfills—all activities that release methane.

For our planet, this has been a profound change. To put it in perspective, today humans are responsible for around 10 percent of the CO₂ entering our atmosphere each year: a small change in percentage terms, but enough to significantly warm the Earth over time. By contrast, we are now responsible for about two-thirds of all methane building up around our planet.³

This massive hike in methane is not only the result of our industries and agriculture. It’s also partly because human-caused climate change is enhancing methane emissions from sources we would once have considered “natural.” “The tricky thing about methane is that the more methane that's released and the hotter the planet gets, the more methane is emitted from traditionally natural sources like wetlands and inland water,” says Desirée Plata, Associate Professor of Civil and Environmental Engineering and Director of the MIT Methane Network. As humans have warmed the planet, for example, we’ve seen higher rates of methane release from wetlands.⁴ “Methane begets methane, so the hotter it gets, the more we accelerate the natural release processes.”

Exact calculations of methane emissions are hard to come by. “Measuring methane is actually quite hard to do,” says Plata, because—even as emissions rise—methane is still quite dilute in the atmosphere. Scientists measure it in two ways: using instruments at ground level near specific methane sources, like near a dairy farm or landfill, and from satellites or airplanes and drones.

The data is better for some forms of methane pollution than others. Landfills, Plata says, “are almost certainly underreported,” while our estimates for coal mine emissions are somewhat clearer.

Despite these uncertainties, the big picture is not in doubt. Humans have vastly increased the amount of methane released into the atmosphere each year, these emissions have sped up in the last decade, and they’ve risen even more sharply since 2020.⁵ In fact, scientists think current methane levels are the highest they’ve been in at least 800,000 years.⁵

“In the last 20 years, methane concentration increases are going gangbusters,” says Plata. “This is like a straight line uphill—think of the craziest roller coaster you’ve ever been on.”

Today, the latest “bottom up” measurements show anywhere from 512 to 849 million metric tons of methane emitted each year, while top-down satellite measurements give a range of 553 to 586 million metric tons.⁵ Scientists don’t try to force these measurements to agree with each other, according to Plata, but use them to understand if their breakdown of different methane sources is realistic.

According to the most recent “bottom up” accounting, which covers the years 2010 to 2019, “natural” emissions such as wetlands, oceans and melting ice layers account for between 183 and 462 million metric tons of methane emissions per year. Coal, oil and gas contribute between 117 and 125 million tons, and agriculture and waste between 195 and 231 million tons.⁵

This methane doesn’t linger in the atmosphere forever. Chemical reactions in the air cause it to degrade into CO₂ within a few years. Some bacteria also use methane to generate the energy they need to survive, which Plata says removes a little less than 10% of all methane in the atmosphere. But as humans have released ever more extreme amounts of methane, these natural “sinks” have not kept pace, allowing the overall level of methane in the atmosphere to more than double since the early 1800s.

“There is an imbalance,” says Plata. “Those sinks are not able to keep up with all the input terms and so this is really what causes the growth of methane in the atmosphere.”

Thank you to Chris Mann of Newquay, United Kingdom, for the question.

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