2011-03-29 13:34:22Yet more positive feedback to GW
Daniel Bailey
Daniel Bailey
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Co-author: "What we're seeing is a system kicking into overdrive. Warming creates more warming."

March 28, 2011

Russia’s boreal forest – the largest continuous expanse of forest in the world, found in the country’s cold northern regions – is undergoing an accelerating large-scale shift in vegetation types as a result of globally and regionally warming climate. That in turn is creating an even warmer climate in the region, according to a new study….

That’s from the University of Virginia news release for a new Global Change Biology study (abstract here).

Back in 2005, Science published an analysis, “Role of Land-Surface Changes in Arctic Summer Warming,” which explained how reduced snow cover and albedo (reflectivity) in the summertime Arctic landscape, caused by global warming, has added local atmospheric heating “similar in magnitude to the regional heating expected over multiple decades from a doubling of atmospheric CO2” (Science, subs. req’d).

That same Science study warned “Continuation of current trends in shrub and tree expansion could further amplify this atmospheric heating 2-7 times.”

The new study looks at a completely different effect:

 

The Great Russian forest, which includes much of Siberia, is the size of the contiguous United States. It has experienced significant documented warming over the last several decades. As a result, tree species that are more tolerant of warmer weather are advancing northward at an increasing rate as species that are less tolerant to a warmer climate are declining in number.

“We’ve identified that the boreal forest, particularly in Siberia, is converting from predominantly needle-shedding larch trees to evergreen conifers in response to warming climate,” said the study’s lead author, Jacquelyn Shuman…. “  This will promote additional warming and vegetation change, particularly in areas with low species diversity.”

…  “What we’re seeing is a system kicking into overdrive,” said co-author Hank Shugart, a U.Va. professor of environmental sciences. “Warming creates more warming.”

The researchers used a climate model to assess what would happen if evergreens continued to expand their range farther north and larch species declined. The “positive feedback” cycle of warming promoting warming showed an increase of absorbed surface warming. The model takes into account detailed information about tree growth rates, and the results agree with actual field studies documenting changes in cone production and movement of evergreen treelines northward….

The Russian boreal forest sits over a tremendous repository of carbon-rich soil frozen in the permafrost. As the forest changes in species distribution from larch to evergreens, warming of the ground surface would cause decomposition of the soil, releasing huge quantities of carbon dioxide into the atmosphere – possibly as much as 15 percent of the carbon dioxide currently in the atmosphere.

“This is not the scenario one would want to see,” Shugart said. “It potentially would increase warming on a global scale.”

Well, actually, the permafrost permamelt contains a staggering “1.5 trillion tons of frozen carbon, about twice as much carbon as contained in the atmosphere, much of which would be released as methane.  Methane is 25 times as potent a heat-trapping gas as CO2 over a 100 year time horizon, but 72 times as potent over 20 years!

tundra-trees.jpg

Going back to the 2005 Science study, 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.”

A 2008 study warns that the warming-driven northward march of vegetation poses yet another threat to the tundra.  That 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.

tundra-fire-2.jpg

The concern is not so much the direct emissions from burning tundra. As the article concludes:

… 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.

The image hows just how much the fire changes the albedo (reflectivity) of the tundra landscape.

A new, very conservative study by NOAA and the National Snow and Ice Data Center — which doesn’t even consider these various amplifying feedbacks in the region — finds that that the thawing permafrost feedback will turn the Arctic from a carbon sink to source in the 2020s, releasing 100 billion tons of carbon by 2100.

Again, the people out there who think R&D or an energy quest is going to stop us from multiple catastrophes are deluding themselves and others.  We need to start aggressive mitigation now as every major independent study concludes.

Related posts and amplifying feedbacks:


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