Climate records from Siberian caves suggest an impending permafrost thaw and a resulting global warming acceleration.
Permafrost regions cover 24% of the northern hemisphere land surface, and hold an estimated 17,000 Gt of organic carbon. Thawing releases CO2 and CH4, creating positive feedback during greenhouse warming.
The researchers, led by Gideon Henderson at the University of Oxford’s Department of Earth Sciences, studied speleothem records from the caves to identify periods where temperatures were above freezing. Speleothems, such as stalactites and stalagmites, form when water seeps through cracks in cave walls, dissolving minerals which precipitate in the air filled cave.
‘Cave temperatures usually approximate the local mean annual air temperature’ says Anton Vaks, the paper’s lead author. ‘When they drop below 0 degrees, the rock above and around the cave freezes, and speleothem growth stops.’
By dating the speleothems and comparing their ages to existing climate records, it is possible to identify the degree of warming which caused the permafrost to melt. New results from Ledyanaya Lenskaya Cave, Eastern Siberia, extend previous records to one million years, and show major deposition of speleothems at around one million years and 400,000 years ago.
‘Both episodes occurred when global temperatures increased 1.5°C ± 0.5 above the pre-industrial level’ says Vaks, ‘showing that this degree of warming is a tipping point for continuous permafrost to start thawing.’
Global temperatures are currently around 0.7 degrees above pre-industrial level, with current models suggesting that a warming of 1.5°C ± 0.5 will be achieved within 10-30 years.
This paper will be presented at the Geological Society’s forthcoming William Smith Meeting, held on 25-27 June, – a meeting that celebrates the 100th anniversary of the beginning of modern dating methods used in the earth sciences. (From: The Geological Society of London. “Siberian caves warn of permafrost meltdown.”Alpha Galileo Foundation, 19 Jun. 2013. Web. 21 Jun. 2013.)