Greenhouse Gas Methane Seeps from Arctic Ice Even in the Depths of Winter

It turns out that the amount of methane gas escaping from the Arctic each year is far higher than expected. Scientists have found that during the long, cold period each winter, more methane is entering the atmosphere than thought.

Methane is a potent greenhouse gas that intensifies atmospheric warming and is about 25 times more potent per molecule than carbon dioxide over a 100-year period. Methane trapped in the Arctic tundra comes primarily from microbial decomposition of organic matter in soil that thaws seasonally. This methane naturally seeps out of the soil over the course of the year, but scientists worry that climate change could lead to the release of even larger emissions from organic matter that is currently stabilized in a deep, frozen soil layer called permafrost.

In this latest study, the researchers focused on the Arctic winter rather than the summer. Most measurements actually focus on the short period of three to four months during the Arctic summer and ignore the lion's share of the year.

"Virtually all the climate models assume there's no or very little emission of methane when the ground is frozen," said Walter Oechel, one of the researchers, in a news release. "That assumption is incorrect."

The water trapped in the soil doesn't freeze completely even below zero degrees Celsius. When the temperatures are right around zero degrees, the top and bottom of the active layer begins to freeze while the middle layer continues to break down organic matter and release methane many months into the Arctic's cold period.

In this case, the researchers found that a major portion of methane emissions during the cold season were observed when temperatures hovered near the zero degrees curtain.

"This is extremely relevant for the Arctic ecosystem, as the zero curtain period continues from September until the end of December, lasting as long or longer than the entire summer season," said Donatella Zona, the study's first author. "These results are opposite of what modelers have been assuming , which is that the majority of the methane emissions occur during the warm summer months while the cold-season methane contribution is nearly zero."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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