In periods with higher tempatures, the permafrost retreats further north. The Lenskaya Ledyanaya Cave lies at 40 degrees north latitude, in an area currently on the border of continuous permafrost. If the temperatures rise another one or two degrees, to approach something like what they were in the interglacial period 400,000 years ago, the situation would most likely look differently. "That is probably the threshold where continuous permafrost becomes vulnerable," says Vaks.
The research is "well-argued and conclusive, the data is great, and it's very diligent," says Hanno Meyer, at the Alfred Wegener Institute for Polar and Marine Research (AWI) in Potsdam, outside Berlin. It was the first time that speleothems have been used to prove the changing areas of southern permafrost borders, he says.
Meyer also said the is currently little information about older warm periods in this region. However, he adds, the research method used by the Oxford University team is not appropriate for other permafrost landscapes because these areas have been frozen for longer than 500,000 years and are therefore too old for the dating method to measure.
The frozen earth varies in thickness from a couple of meters to 1.5 kilometers, depending on the area. And a large portion of the permafrost areas lie farther north than Vaks and his team have studied until now, with pieces even in the ocean floor. So what does this newly released research now mean for these areas in the high Arctic? "We understand that we must go further to the North," admits Vaks. Over the next two years, Vaks and his team will look for more northern caves -- and for speleothems that can be dated.