BBC: Evidence from Siberian caves suggests that a global temperature rise of 1.5C could see permafrost thaw over a large area of Siberia.
A study shows that more than a trillion tonnes of the greenhouse gases CO2 and methane could be released into the atmosphere as a result.
An international team has published details in the journal Science.
The evidence comes from analysis of stalactites and stalagmites in caves along the "permafrost frontier".
This is where ground begins to be permanently...