Permafrost climate tipping point threshold at 1.5 degrees - Siberian caves reveal

At what point might we trigger a permafrost tipping point? New research from the caves of Siberia points to a threshold temperature of just 1.5 degrees celsius. At that temperature we could see large swathes of permafrost across Siberia melting resulting in the release of more than 1,000 gigatons of carbon and methane. This would be a substantial climate feedback resulting in even greater global warming. There would also be substantial damage to natural and human environments and structures.

And we are already halfway there to warming the world by 1.5C, with an estimated global temperature rise since the Nineteenth century of between 0.7 and 0.8 degrees C. There is already enough inertia in the climate system to carry us over this threshold. Which makes every attempt to reduce carbon emissions, and the use of fossil fuels, as worthwhile to limit the permafrost thaw.

Related: Methane and CO2 in thawing Arctic permafrost a climate tipping point | "We do have an emergency" - Arctic Methane Feedback amplifying warming | Arctic Permafrost thawing raising CO2 levels


The study lead by scientists from Oxford University examined stactites and stagmites in caves in a north south transect. These stalagmite and stalagtite structures only grow when there is liquid rainwater and snow melt drips through the caves. The formations in the caves document permafrost conditions over the last half a million years, through warmer periods and ice ages.

An example from a particularly warm period about 400,000 years ago suggest that global warming of 1.5°C triggers substantial permafrost thaw.

"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," said Dr Anton Vaks of Oxford University's Department of Earth Sciences, who led the work. "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."

Cave formations were dated using radiometric dating techniques. According to data from the Ledyanaya Lenskaya Cave - near the town of Lensk latitude 60°N - in the coldest region showed that the only period when stalactite growth took place occurred about 400,000 years ago, during a period with a global temperature 1.5°C higher than today. Periods when the world was 0.5-1°C warmer than today did not see any stalactite growth in this northernmost cave. This suggests that around 1.5°C is the 'tipping point' at which the coldest permafrost regions begin to thaw, said the scientists.

The scientists say they need to find more caves further north in Siberia.

Dr Vaks said: "Although it wasn't the main focus of our research our work also suggests that in a world 1.5°C 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."

Note: At the head of this story I have embedded a video by Peter Sinclair, an informative video published on youtube. for the Yale Forum on Climate Change and the media which includes an interview with Dr Anton Vaks, as well as featuring other climate scientists. Some of this footage was included in my December 2012 post: Methane and CO2 in thawing Arctic permafrost a climate tipping point.

Sources:

• Oxford University media release, 22 Feb 2013 - Caves point to thawing of Siberia
  
• A. Vaks, O. S. Gutareva, S. F. M. Breitenbach, E. Avirmed, A. J. Mason, A. L. Thomas, A. V. Osinzev, A. M. Kononov, G. M. Henderson, Speleothems Reveal 500,000-Year History of Siberian Permafrost (abstract), in Science 21 Feb 2013, Science DOI: 10.1126/science.1228729