An international team of scientists said that the Arctic went through ice-free periods of extreme warmth over the past 2.8 million years, based on a new analysis of sediment in Russia.

The team led by Martin Melles of the University of Cologne, Germany, drilled into an iced-over lake formed by a meteorite impact on the Chukchi Peninsula in Siberia for the longest sediment core ever collected.

Since the meteorite struck an area of Lake El’gygytgyn that was not eroded by glaciers, the sediment record reaches back nearly 30 times further in time than ice cores from Greenland that cover the past 110,000 years.

The sediment reveals periods of extreme warmth that show the polar regions are much more vulnerable to change than previously thought and are difficult to explain by greenhouse gases alone, said the study in the journal Science.

Scientists have long known that the Arctic went through climate cycles but the latest research shows some of these warm phases were “exceptional”, with temperatures 4°C to 5°C warmer and 30 centimetres wetter than during normal interglacials, the study said.

Two of these “super-interglacials” happened about 400,000 years ago and 1.1 million years ago, and the data suggests it was virtually impossible for Greenland’s ice sheet to have existed in its present form at those times.

But just what caused these extreme changes remains a mystery.