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Permafrost—the ground that stays frozen for two or more consecutive years—is a ticking time bomb of climate change. Some 24 percent of Northern Hemisphere land is permafrost. That’s 9 million square miles (23 million square kilometers) found mostly in Siberia, the Tibetan Plateau, Alaska, the Canadian Arctic, and other higher mountain regions.

Unfortunately, thawing permafrost releases massive amounts of methane and/or carbon dioxide. The question is whether that would happen over the course of decades or over a century or more. This short video from the Yale Climate Forum explains the current scientific thinking on just how close we might be to the lethal tipping point.

Meanwhile this 90-second permafrost primer from the Climate Desk explains exactly we want this northern freezer to remain frozen.

The map below shows land-based permafrost in the Northern Hemisphere. It also shows the subsea permafrost that underlies the continental shelves of the Arctic Ocean.

We really really don’t want permafrost to melt since its emissions have the potential to dwarf our own. As the Yale Climate Forum video says, we have the theoretical ability to control our carbon emissions but none whatsoever to stop a permafrost tipping point once it’s reached.