When permafrost thaws, the frozen organic matter inside it will thaw out, too, and begin to decay. As organic matter decays, it gets eaten up and digested by microbes. The bacteria that eat it produce either carbon dioxide or methane as waste. If there is oxygen available, the microbes make carbon dioxide. But if there is no oxygen available, they make methane. When permafrost carbon turns into methane, it bubbles up through soil and water. On the way, other microorganisms eat some of it. But some methane makes it to the surface and escapes into the air. Warmer temperatures mean that permafrost can thaw and release methane to the atmosphere. But warming also means that the growing seasons in Arctic latitudes will last longer. When the growing season is longer, plants have more time to suck up carbon from the atmosphere. Since carbon in the air is what plants use to grow, it can also act as a sort of fertilizer under certain conditions. Then plants grow faster and take up even more carbon. This means that plants take up carbon during the growing season, but do not release as much carbon through decay. So we say that the Arctic acts as a carbon sink. But as the Earth continues to warm, and a lot of permafrost thaws out, the Arctic could become an overall source of carbon to the atmosphere, instead of a sink. This is what scientists refer to as a tipping point. We say that something has reached a tipping point when it switches from a relatively stable state to an unstoppable cycle. In this case, the Arctic would change from a carbon sink to a carbon source. If the Arctic permafrost releases more carbon than it absorbs, it would start a cycle where the extra carbon in the atmosphere leads to increased warming. The increased warming means more permafrost thawing and methane release. Credits: https://nsidc.org/cryosphere/frozenground/methane.html
Posted on: Wed, 05 Nov 2014 11:52:00 +0000
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