Soil temperatures in permafrost regions around the world have increased over the past decade, according to a new study by the Global Terrestrial Network for Permafrost (GTN-P).
Warming was most apparent in Siberia, where the temperature of frozen soil increased by about one degrees Celsius.
Permafrost refers to the ground - including soil or rocks - which has remained frozen for two or more consecutive years. About one-sixth of the land area on Earth comprises permafrost regions.
Scientists believe permafrost warming could amplify global climate change, as thawing of frozen sediments would expose billions of tonnes of organic carbon to micro-organisms that would decompose the organic matter and release millions of tonnes of carbon dioxide and methane into the atmosphere.
To investigate changes in permafrost temperatures around the world, the research team measured the temperature of soil at depths greater than 10 metres in 154 boreholes in the Arctic, Antarctic and several other high mountain ranges for ten years.
Most of the 154 boreholes were drilled during the International Polar Year 2007/08, and were equipped with temperature measuring equipment.
Of all boreholes monitored, 123 boreholes enabled researchers to draw conclusions for an entire decade. The data from remaining 31 boreholes was used to update calculations on annual deviation.
The results showed that the temperature of the permafrost soil increased at 71 of the 123 measuring sites during the period from 2007 to 2016. The permafrost in five boreholes was found in the state of thawing.
Soil temperature decreased at 12 boreholes (individual sites located in southern Eurasia, eastern Canada, and on the Antarctic Peninsula).
For 40 boreholes, the temperature was observed to have remained almost unchanged.
The most significant permafrost warming was noticed in the Arctic region.
"There, in regions with more than 90 per cent permafrost content, the soil temperature rose by an average of 0.30 degrees Celsius within ten years," said Dr Boris Biskaborn, the first author of the study and a member of the research group Polar Terrestrial Environmental Systems.
For Arctic regions with less than 90 per cent permafrost, an increase of 0.2 degrees Celsius on average was noticed.
Scientists were surprised to find temperature increasing by 0.90 degrees Celsius or even higher at some boreholes in northeast and northwest Siberia.
In the Himalayas, in the Alps and in the mountain ranges of the Nordic countries, the temperature of the permanently frozen soils was up by an average of 0.19 degrees Celsius.
"All this data tells us that the permafrost isn't simply warming on a local and regional scale, but worldwide and at virtually the same pace as climate warming, which is producing a substantial warming of the air and increased snow thickness, especially in the Arctic," said Professor Guido Grosse, head of the Permafrost Research Section at the Alfred Wegener Institute in Potsdam.
The findings of the study are published in journal Nature Communications.
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