Study of Siberian permafrost caves shows global warming of just 1.5C 'would pump out a TRILLION tonnes of methane and CO2'

U.N. studies show global temperatures have already risen by 0.7C



Huge increase in levels of CO2 could accelerate global warming



Infrastructure built on top of permafrost across the world would collapse

Governments currently committed to no more than 2C climate change



A temperature rise of just 1.5C is likely to release vast amounts of greenhouse gas into the atmosphere from melting permafrost, new evidence suggests.

In Siberia alone, the mighty thaw would liberate more than 1,000 gigatonnes of carbon dioxide and methane, experts warn.

The extra levels of greenhouse gas are potentially enough to accelerate global warming. Natural ecosystems and human infrastructure would also be seriously disrupted.

Frost crystals at the entrance of Ledyanaya Lenskaya Cave: In Siberia alone, a thaw spurred by global warming of just 1.5C would liberate more than 1,000 gigatonnes of carbon dioxide and methane, experts warn

Governments around the world have set themselves the goal of pegging global warming at less than 2C higher than pre-industrial levels.

Above this point, it is feared climate change could become impossible to control.

But the new research suggests the tipping point at which large frozen regions of the Earth start to thaw may be a warming of just 1.5C.

A global rise of 1.5C above late 19th century temperatures could bring a substantial thaw as far north as 60 degrees latitude, it warns.

Sixty degrees girdles the world through Siberia, the Nordic nations, the southern tip of Greenland, Canada and south Alaska. U.N. studies show that temperatures have already risen by about 0.7C since the 19th century and are still rising.

The permafrost frontier: Here the ground is permanently frozen in a layer tens to hundreds of metres thick

The evidence comes from a study of stalactites and stalagmites in caves along the 'permafrost frontier' of Siberia. Here, the ground starts to become permanently frozen in a layer tens to hundreds of metres thick.

The mineral formations that hang from the roofs of caves or rise from their floors only grow in the presence of liquid water. They form as liquid rainwater or melting snow and ice drips into the caves.

In Siberia, the formations record 500,000 years of changing permafrost conditions.

The evidence showed that 400,000 years ago, a temperature 1.5C warmer than it is today was enough to cause substantial thawing of the permafrost.

Dr Anton Vaks, from Oxford University, led the international team, whose work is reported in the latest online version of the journal Science.

He said: 'The stalactites and stalagmites from these caves are a way of looking back in time to see how warm periods similar to our modern climate affect how far permafrost extends across Siberia.

'As permafrost covers 24 per cent of the land surface of the northern hemisphere significant thawing could affect vast areas and release gigatonnes of carbon.

'This has huge implications for ecosystems in the region, and for aspects of the human environment.

'For instance, natural gas facilities in the region, as well as power lines, roads, railways and buildings are all built on permafrost and are vulnerable to thawing.

'Such a thaw could damage this infrastructure with obvious economic implications.'

An ice hall in the Ledyanaya Lenskaya Cave: Stalactites and stalagmites only grow in the presence of liquid water. By dating them researchers worked out when they last grew and what the global temperatures were The team measured the radioactive decay of minerals to date the growth of stalactites and stalagmites in the caves. Results from Ledyanaya Lenskaya Cave in the northernmost and coldest region, near the town of Lensk, showed that stalactite growth only took place there 400,000 years ago when the temperature was higher by 1.5C. Periods when the world was 0.5 - 1C warmer than it is today did not see any stalactite growth in the cave. This suggested that 1.5C was the 'tipping point' at which the coldest permafrost regions began to thaw. The United Nations Environment Programme (UNEP) estimates that permafrost contains about 1,700billion tonnes of heat-trapping carbon - twice the amount currently in the atmosphere. A UNEP report said in December that permafrost had already begun to thaw in some areas and could release between 43 and 135billion tonnes of carbon dioxide, the main greenhouse gas, by 2100.

An environment under threat: A view of the frozen Lena River from the entrance of Ledyanaya Lenskaya Cave

Almost 200 nations agreed to the 2C limit on global temperatures above pre-industrial times - comparable to late 19th century temperatures - to avert more floods, storms and rising sea levels.

More than 100 poor nations want a tougher ceiling of 1.5C. But it is slipping out of reach because greenhouse gas emissions are rising, especially in emerging nations led by China and India, while some rich nations are not making promised cuts.