Forests and fires foster fearsome feedbacks
Previously, I looked at why the permafrost won’t be perma for long. Then I looked at whether the potential destruction of the tundra represents the point of no return for the climate, necessitating that we keep atmospheric concentrations of carbon dioxide below 450 ppm or else risk going to 800 ppm to 1,000 ppm. Here I examine two local amplifying feedbacks that further threaten the permafrost: forests and fires.
Reduced snow cover and albedo (reflectivity) in the summertime Arctic landscape, caused by global warming, has added local atmospheric heating ($ub. req’d) “similar in magnitude to the regional heating expected over multiple decades from a doubling of atmospheric CO2.” That same Science study warns “Continuation of current trends in shrub and tree expansion could further amplify this atmospheric heating 2-7 times.”
The point is that if you convert a white landscape to a boreal forest, the surface suddenly starts collecting a lot more solar energy. That trend is occurring now, as seen in these two photos from a recent ScienceNews article, “Boreal forests shift north.”
“Upper photo taken in 1962 shows tundra-dominated mountain slope in Siberian Urals. A 2004 photo of the same site, below, shows conifers were setting up dense stand of forest.”
Now, another major study warns that the warming-driven northward march of vegetation poses yet another threat to the tundra.
The study, “Frequent Fires in Ancient Shrub Tundra: Implications of Paleorecords for Arctic Environmental Change,” finds:
… greater fire activity will likely accompany temperature-related increases in shrub-dominated tundra predicted for the 21st century and beyond. Increased tundra burning will have broad impacts on physical and biological systems as well as on land-atmosphere interactions in the Arctic, including the potential to release stored organic carbon to the atmosphere.
… studies of modern tundra fires suggest the possibility for both short- and long-term impacts from increased summer soil temperatures and moisture levels from altered surface albedo and roughness, and the release soil carbon through increased permafrost thaw depths and the consumption of the organic layer.
Click on the image above to see just how much the fire changes the albedo of the tundra landscape.
We must get serious about reducing greenhouse-gas emissions now, since the consequences of hitting 1,000 ppm are simply too dire to risk.
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