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Siberian cave study warns of permafrost thaw tipping point

By Robert Myles     Feb 24, 2013 in Science
Evidence assembled from stalactite and stalagmite formations in frozen caves in Siberia by a team of international scientists led by Oxford University gives some clues as to what might happen if global temperatures continue to rise.
The Oxford scientific team which included researchers from the UK, Russia, Mongolia and Switzerland postulate that a global temperature rise of 1.5°C could cause a thaw to set in over the permafrost zone, those huge areas of permanently frozen ground in Siberia — and we may already have passed the point of no return. Their analysis is published this week in Science magazine.
The scientists estimate that a thaw in the Siberian permafrost could release over 1,000 gigatonnes of the greenhouse gases carbon dioxide and methane into Earth’s atmosphere. The big worry is methane which is 20 times more potent than carbon dioxide as a greenhouse gas in trapping the Sun’s heat in the Earth’s atmosphere.
The Oxford University team were studying stalactites and stalagmites along the ‘permafrost frontier,’ an imaginary demarcation line where the ground starts to become permanently frozen at depths of anything between ten to hundreds of metres in depth. Since stalactites and stalagmites only increase in size when liquid water is present, in Siberia’s case as a result of snow and ice melt, the cave formations found provided a temperature record stretching back half a million years. The growth of stalactites and stalagmites stopped during cool periods as temperatures fell and the permafrost refroze. By analysing the growth structure of the cave formations, scientists were able to gauge changing permafrost conditions and date earlier warm periods in the Earth’s climate similar to what is being experienced today.
Of particular interest to the Oxford team was a warm period known as the Marine Isotopic Stage 11 an inter-glacial period which occurred between 424,000 and 374,000 years ago. A study of this period showed that global warming of 1.5°C, compared to global temperatures in the modern era prior to the industrial revolution, was sufficient to cause a thaw in the Siberian permafrost far to the north of its present-day southern extent.
Dr Anton Vaks of Oxford University's Department of Earth Sciences, who led the work, said, “The stalactites and stalagmites from these caves are a way of looking back in time to see how warm periods similar to our modern climate affect how far permafrost extends across Siberia.”
“As permafrost covers 24% of the land surface of the Northern hemisphere significant thawing could affect vast areas and release giga-tonnes of carbon.”
“This has huge implications for ecosystems in the region, and for aspects of the human environment. For instance, natural gas facilities in the region, as well as power lines, roads, railways and buildings are all built on permafrost and are vulnerable to thawing. Such a thaw could damage this infrastructure with obvious economic implications.”
Radiometric dating techniques were used to date the stalactites and stalagmites. Data taken from the Ledyanaya Lenskaya Cave — near the town of Lensk at latitude 60° North — revealed that the only time when stalactite growth took place was around 400,000 years ago when global temperatures were 1.5°C higher than today. Other periods, when the world temperatures were in the range 0.5°C to 1°C did not show any stalactite growth meaning the permafrost remained frozen.
Dr Vaks commented, “Although it wasn't the main focus of our research our work also suggests that in a world 1.5 degrees Celsius warmer than today, warm enough to melt the coldest permafrost, adjoining regions would see significant changes with Mongolia's Gobi Desert becoming much wetter than it is today and, potentially, this extremely arid area coming to resemble the present-day Asian steppes.”
The data suggested that an increase in temperatures of 1.5°C was the tipping point at which the coldest areas of permafrost begin to thaw. If that should happen, and the point may not be far off when it does, it will have global implications.
New Scientist refers to thaw of the Siberian permafrost being a particular danger, stating that if a large region called the Yedoma begins to thaw, runaway decomposition could set in. In this process, because dormant microbes in the soil would eat carbon and produce heat, more permanently frozen soil would then start to melt in turn releasing yet more greenhouse gases.
Permafrost tipping point already reached?
As the same article highlights, we may already have reached the point of no return or at least can do nothing to stop the Earth arriving at the permafrost tipping point. New Scientist reports that between 1850 and 2005, global temperatures rose by 0.8°C according to the 2007 report of the Intergovernmental Panel on Climate Change. If Mankind were to arrest emission of all greenhouse gases today, temperatures are projected to continue to rise a further 0.2°C over the next two decades. That scenario leaves a safety margin of 0.5°C but of course the reality is that greenhouse gas emissions are not in decline. Quite the reverse, in fact.
As industrialization takes hold in large, newly emerging economies like China, India and Brazil. On top of that, despite many governments agreeing the necessity of adopting green energy sources, new fossil fuel power stations coming on stream will continue to add to the greenhouse gas mix in the atmosphere for decades to come.
The full report headed by The University of Oxford’s Department of earth Sciences is published this week in Science under the title 'Speleothems reveal 500 kyr history of Siberian permafrost'
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