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Thu Mar 19, 2020, 11:15 AM

Risk Of Abrupt Permafrost Thaw Grows; IPCC Doesn't Take Rapid GHG Releases Into Account

Small scale permafrost slump. Photo credit: NPS Climate Change Response on Visual Hunt / CC BY.

The cracked, buckling road between Fairbanks and Fox, Alaska, wends its way past snowy forests where slender birches and black spruce trees protrude out of the ground at impossible angles, slanting and swaying as if the very earth were alive. Scientists call these “drunken forests.” The ground here consists of permafrost — soil, sediment, rock and ice that often remains at or below 0 degrees Celsius (32 degrees Fahrenheit) year-round. Permafrost covers approximately 22.8 million square kilometers (8.8 million square miles) in the Arctic, sub-Arctic and alpine regions — comprising nearly a quarter of the exposed land surface in the northern hemisphere.

In Alaska, 85 percent of the state lies within the permafrost zone, though discontinuous permafrost — areas with patchy permafrost presence — underlies much of the Fairbanks area. In Arctic regions, permafrost temperatures often dip down to -8 degrees C (-17.6 degrees F). But in Fairbanks, which lies roughly 321 kilometers (200 miles) south of the Arctic Circle, temperatures hover much closer to the freezing point, causing the permafrost to sporadically thaw out. This freeze-thaw action has long posed challenges for natural and human systems, intoxicating forests, breaking pavement, sinking houses, and even sometimes draining lakes sitting atop it.




Abrupt thaw, the large-scale surface subsidence of land, occurs in zones rich with subsurface ice and manifests as thermokarst, thaw slumps producing gullies, scar wetlands and thermokarst lakes. As temperatures rise, ice wedges or lenses can melt rapidly, destabilizing soil and sediment above in a way akin to suddenly removing a support beam in a house, resulting in structural collapse. Unlike gradual thaw which affects mere centimeters of permafrost and occurs over the time scale of decades, abrupt thaw can impact meters of permafrost in just months or years. This can shock the surrounding landscape into releasing even more carbon than if it had thawed at a leisurely pace.

In a paper published in February in Nature Geoscience, Turetsky and her co-authors found that, while abrupt thaw will likely occur in less than 20% of the world’s permafrost zone, it could affect half of all permafrost carbon through rapid erosion, collapsing ground and landslides. Despite influencing only a small portion of the Arctic, abrupt thaw emissions could have the same climate feedback effect as gradual thaw emissions would over the entire permafrost zone. These abrupt releases could trigger a positive feedback loop whereby the permafrost’s greenhouse gas emissions would further warm the atmosphere, which would then thaw more permafrost and release more carbon. Turetsky says that without accounting for abrupt thaws, we’re underestimating the impact of permafrost carbon releases by 50 percent.



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