Siberian Caves Reveal Advancing Permafrost Thaw
Melting of significant portions of Arctic permafrost could accelerate climate change into a catastrophe
By David Biello
... Geoscientist Anton Vaks of the University of Oxford led an international team of experts—including the Arabica Caving Club in Irkutsk—in sampling the spindly cave growths known as stalagmites and stalactites across Siberia and down into the Gobi Desert of China. Taking samples of such speleothems from six caves, the researchers then reconstructed the last roughly 500,000 years of climate via the decay of radioactive particles in the stone. When the ground is frozen above a cave no water seeps into it, making such formations "relicts from warmer periods before permafrost formed," the researchers wrote in a study published online in Science on 21 February.
The details of the study reveal that conditions were warm enough even in Siberia for these mineral deposits to form roughly 400,000 years ago, when the global average temperature was 1.5 degrees Celsius higher than present. It also suggests that there was no permafrost in the Lena River region at that time, because enough water seeped into the northernmost cave to enable roughly eight centimeters of growth in the formations.
That was, in fact, the last time the formations in the Ledyanaya Lenskaya Cave grew, although other caves further south showed multiple periods of growth coinciding with other warmer periods. "That boundary area of continuous permafrost starts to degrade when the mean global temperature is 1.5 degrees C higher than present," Vaks explains. "Such a warming is a threshold after which continuous permafrost zone starts to be vulnerable to global warming."
Since Vaks's present is the "preindustrial late Holocene," that means the planet is already more than halfway there, having experienced 0.8 degree C warming to date. Such a thaw is no small matter, given that permafrost covers nearly a quarter of the land in the Northern Hemisphere and holds roughly 1,700 gigatonnes of carbon—or roughly twice as much carbon as is currently trapping heat in the atmosphere. Much of that carbon would end up in the atmosphere if the permafrost was to thaw further ...
http://www.scientificamerican.com/article.cfm?id=siberian-caves-reveal-permafrost-thaw
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