Friday, March 25, 2016

The Arctic Is Thawing Much Faster than Expected, Scientists Warn

The marshy, tundra landscape surrounding Newtok is seen from a plane on July 6, 2015 outside Newtok, Alaska. (Photo Credit: Andrew Burton/Getty Images) Click to Enlarge.
Amid blowout warm temperatures in the Arctic this year, two new studies have amplified concerns about one of the wild cards of a warming planet — how quickly warming Arctic soils could become major contributors of greenhouse gases to the atmosphere, causing still greater warming.

In a major international study published last week in Nature Geoscience, a team of researchers from regions ranging from Alaska to Russia report that permafrost is thawing faster than expected — even in some of the very coldest areas.

In these regions, winter freezing cracks open the ground, which then fills with water in the summer from melting snow.  When refreezing occurs in the winter, that causes large wedges of ice to form amid the icy ground.  These ice wedges can extend ten or fifteen meters deep, and can in some cases be thousands of years old.

But the study, sampling high Arctic sites in Russia, Alaska, and Canada based on both field studies and satellite observations, found that across the Arctic, the tops of these wedges are melting, as the top layer of permafrost soil — which itself lies beneath a so-called “active layer” of soil that freezes and thaws regularly — also begins to thaw.  “Landscape-wide ice-wedge degradation was observed at ten out of eleven sites,” the paper reported.
The problem is that as these frozen soils thaw, even for part of the year, microorganisms living within them can begin to break down dead but preserved plant life from eons past, and release their carbon in the form of carbon dioxide or methane.  Co-author Vladimir Romanovsky says he thinks that the Earth’s atmosphere already contains more greenhouse gases than it might otherwise due to this thawing.

It has been estimated that Arctic permafrost contains roughly twice as much total carbon in its frozen depths as the entire planetary atmosphere does, because these landscapes have slowly stored it up over vast time periods.
There have been at least some arguments that there may be other factors that offset permafrost carbon emissions.  Some have suggested, for instance, that more plants will grow in the warmer Arctic, sequestering more carbon, and that this will help offset permafrost losses.

But in the second study, just published in Environmental Research Letters, an expert assessment of nearly 100 Arctic scientists found little reason to believe there will be any factor that offsets permafrost emissions enough to reduce the level of worry.

The expert assessment led to the conclusion that, as the paper puts it, “Arctic and boreal biomass should not be counted on to offset permafrost carbon release and suggests that the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario.”

These studies of permafrost are critical because of the underlying math of the climate change problem.  There is a hard limit to how many greenhouse gases can be emitted if we want to avoid a given level of warming — say, 1.5 degrees Celsius or 2 degrees Celsius above pre-industrial levels.
Permafrost has the potential to upend all of that.  The last thing the world needs, as it creaks into action to reduce emissions, is the emergence of a major new source of them, brought on by warming itself.  Yet that’s exactly what we’re talking about here.

Granted, precisely how much carbon permafrost can emit and how fast that can happen remain big uncertainties.  But given current scientific understanding, it could easily be well over 100 gigatons of carbon dioxide by the end of the century, or one tenth of the remaining carbon budget. In fact, it could be more than that.

Read more at The Arctic Is Thawing Much Faster than Expected, Scientists Warn

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