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Scientists greatly underestimating methane emitted by humans

According to a new study, humans have been emitting a lot more methane than scientists thought. Photo by Stephen Shaver/UPI
According to a new study, humans have been emitting a lot more methane than scientists thought. Photo by Stephen Shaver/UPI | License Photo

Feb. 19 (UPI) -- Over the last three centuries, methane emissions have increased 150 percent. Scientists have previously struggled to determine the origins of this increase.

Though methane can be released naturally, a new study -- published Wednesday in the journal Nature -- suggests scientists have been greatly underestimating the amount of methane released by humans during the last 300 years.

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Of the greenhouse gases released by humans, methane is the second largest contributor to global warming. Carbon dioxide is first.

As a greenhouse gas, methane is different than CO2 in two ways. First, its warming effect is much more potent than CO2, and second, its lifespan is much shorter. Carbon dioxide can remain in the atmosphere for roughly a century, whereas methane is gone within nine years.

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Both factors mean methane emissions reductions would have immediate effects on the trajectory of climate change.

"If we stopped emitting all carbon dioxide today, high carbon dioxide levels in the atmosphere would still persist for a long time," Benjamin Hmiel, postdoctoral researcher at the University of Rochester, said in a news release. "Methane is important to study because if we make changes to our current methane emissions, it's going to reflect more quickly."

Because methane emissions are more potent and underestimated, there is a greater potential for regulations to impact global warming.

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"Placing stricter methane emission regulations on the fossil fuel industry will have the potential to reduce future global warming to a larger extent than previously thought," Hmiel said.

Hmiel and his colleagues were able to calculate changes in human-caused methane emissions by measuring the concentration of certain carbon isotopes in ancient air samples. Fossilized methane, the kind trapped in ancient hydrocarbon deposits and released by human activities, is without carbon-14, a rare radioactive isotope. Biological methane, on the other hand, features significant concentrations of carbon-14.

Researchers sourced their ancient air samples from ice cores collected in Greenland. When ice freezes, tiny bubbles of air get trapped in the layers. Scientists used a melting chamber to extract the ancient air from the tiny bubbles.

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Chemical analysis of ancient air bubbles showed biological sources accounted for the vast majority of methane in the air prior to the Industrial Revolution, which began around 1870. The amount of fossilized methane found in the air began to rise dramatically after humans began using fossil fuels.

Fossilized methane can be released by geologic seeps, but according to the study's authors, such natural processes can't account for such a sudden shift in the amount of fossilized methane being released into the atmosphere.

The new analysis suggests scientists have previously overestimated the amount of methane being released into the atmosphere via natural processes, and as a result, underestimate the amount of human-caused methane emissions by 25 to 40 percent.

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Hmiel and his colleagues claim their findings are actually good news, as the research means reducing fossil fuel emissions will have a greater impact on curbing rising global temperatures.

"I don't want to get too hopeless on this because my data does have a positive implication: most of the methane emissions are anthropogenic, so we have more control," Hmiel said. "If we can reduce our emissions, it's going to have more of an impact."

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