Forests reached the Arctic Ocean at the time, the scientists conclude, and permafrost was not widespread. Picture: k-ozeru.ru

They found from analysis of sediments that 3.6 million years ago this crater lake - formed by a meteor - was in a zone of forests with temperatures a full 8C warmer than today. At the time, when there was no industrial pollution, greenhouse gases were at much the same levels as today.

'The Arctic was a very different place', Julie Brigham-Grette of the University of Massachusetts Amherst, the lead US scientist on the study, told RIA Novosti.

There was in all probability no Arctic ice sheet at the time, said reports of the study which also involved Russian and German experts.

Drilling into the sediment of the lake, they obtained a unique time capsule of conditions above the Arctic Circle spanning millions of years.

The US academic singled out partners Pavel Minyuk of Russia's Northeast Interdisciplinary Scientific Research Institute in Magadan and Martin Melles of the University of Cologne in Germany, stressing there was 'fabulous international collaboration' in research where the findings about the past may be a guide to the future.

Lake Elgygytgyn, formed in a crater with an 18km diameter rim, lies almost 100 km north of the Arctic Circle in the region of Chukotka.

Some 3.6 million years ago 'it was almost eight degrees Celsius warmer in summer than it is now', she said.

Global warming sensation: Arctic land masses were once warm, forested and the North Pole had no ice cover. Pictures: The Siberian TImes, University of Massachusetts Amherst, Lake Elgygytgyn Drilling Project

Forests reached the Arctic Ocean at the time, the scientists conclude, and permafrost was not widespread.

Conditions were far milder than today's extremes, and - significantly - greenhouse gases appear to have been at similar levels.

'We're learning a lot of new things from it about how sensitive the Earth's system, and particularly the Arctic, is to really small changes in carbon dioxide and other parameters,' she said.

She was quoted saying: 'Our best estimates for CO2 that we have for the Pliocene era, which was from about 5 million to 1.8 million years ago, is in the range of what we have today, 320 to 400 parts per million.

'We're going to hit 400 parts per million later this year.'

Which means that today's global warming is a return to conditions that used to prevail in the Pliocene era.

'What's happening today with our increasing CO2 is that global temperatures are rising and, some people would argue, we're heading to a situation like what was going on in the Pliocene - we see tree lines marching further north, permafrost starting to decay, the Greenland ice sheet starting to melt away quickly, sea surface temperatures rising,' she said.

'Just as Earth took a while to cool down after the end of the Pliocene era, one of the implications of the study is that Earth today is trying to catch up to the level of warming that we've put into the atmosphere.

'So there's a lag between how fast the earth's system can respond and the extremely rapid way humans are increasing CO2.

International researchers have gleaned these extraordinary hidden scientific secrets by drilling 318 metres into a unique lake in northeastern Siberia. Pictures: google maps

Previous findings from the study have suggested that extreme warm periods in the Arctic correspond closely with times when parts of Antarctica were also ice-free and warm, suggesting a strong connection between Northern and Southern Hemisphere climate.

The lake was formed 3.6 million years ago when a huge meteorite hit Earth, leaving an 11-mile-wide crater. It's been collecting layers of sediment ever since.

The lake is of interest to scientists because it has never been covered by glaciers. That has allowed the uninterrupted build-up of sediment at the bottom of the lake, giving a treasure trove of previously undiscovered information on climate change.

Researchers drilled three holes, obtaining a more perfect time chart than in Greenland.

At the time one journal headline read: 'The thrill to drill in the chill'. But it is clear their findings are attracting serious scientific interest.

The samples were extracted in 2009 and flown by special cargo plane from Siberia to St Petersburg and then to a laboratory in Germany.

'Studying high-latitude systems is of great importance to an understanding of Earth's climate at all latitudes,' said Paul Filmer, programme director in the National Science Foundation (NSF)'s Division of Earth Sciences in America, which co-funded the expedition to the Siberian lake.

'Of primary interest is determining why and how the Arctic evolved from a warm forested ecosystem to a cold permafrost ecosystem between two and three million years ago'.



All pictures below courtesy University of Massachusetts Amherst, Lake Elgygytgyn Drilling Project