Melting permafrost is emerging as a new factor in climate change, allowing long-frozen carbon to be released into the air and accelerating global warming, the UN Environment Programme (UNEP) said on Tuesday (UNEP).

In a report issued as the annual round of UN climate talks entered their second day, UNEP said scientists had already pronounced thawing permafrost to be a worry but the issue remained off politicians' radar.

"Its potential impact on the climate, ecosystems and infrastructure has been neglected for too long," warned UNEP excutive director Achim Steiner.

"This report seeks to communicate to climate-treaty negotiators, policy makers and the general public the implications of continuing to ignore the challenges of warming permafrost."

Permafrost covers huge tracts of northern Siberia and Canada, as well as parts of China and the United States.

It comprises an "active" layer at the surface, up to two metres (6.5 feet deep), which melts in summer and refreezes in winter, and beneath it is permanently frozen soil.

If warming penetrates this under-layer, it could release vast amounts of carbon dioxide (CO2) and methane from vegetation deposited thousands of years ago but which until now have been safely locked up in ice.

These greenhouse gases would enter the atmosphere, adding to warming, which then accelerates the permafrost melt -- a vicious circle known in scientific parlance as a feedback.

The UNEP report said that the feedback scenario, first sketched by ice scientists about a decade ago, is becoming a real source of concern.

Arctic and alpine air temperatures are expected to increase at roughly twice the global rate.

So an average worldwide temperature increase of three degrees Celsius (5.4 degrees Fahrenheit) would translate into a massive 6 C (10.8 F) rise in the far north, resulting in loss of anywhere between 30 to 85 per cent of near-surface permafrost.

Warming permafrost could emit 43-135 gigatonnes of CO2-equivalent by 2100 and 246-415 gigatonnes by 2200, a warming that would persist for centuries, the study said.

By way of comparison, some 375 billion tonnes of carbon have been released into the atmosphere since the start of the industrial age in about 1750, mainly through the burning of coal, oil and gas, according to the World Meteorlogical Organisation (WMO).

"The release of carbon dioxide and methane from warming permafrost is irreversible," said the report's head author, Kevin Schaefer, from the University of Colorado's National Snow and Ice Data Center.

"Once the organic matter thaws and decays away, there is no way to put it back into the permafrost."

The report suggests the Nobel-winning Intergovernmental Panel on Climate Change (IPCC) draw up a special report on how permafrost emissions could affect climate policy.

It also recommends creating "national permafrost monitoring committees" that would regularly scrutinise permafrost levels, expand coverage and standardise their measurements.

Politicians eyeing a worldwide treaty on climate "need to account for these emissions or we risk overshooting the 2C (3.6 F) maximum warming target," said Schaefer at a press conference.

The 12-day talks in Qatar seek to stride towards a new global pact on climate that would be sealed in 2015 and take effect in 2020.

But they take place against a backdrop of surging carbon emissions as emerging giants, led by China, burn coal to power their rise out of poverty and the switch to cleaner fuels in rich countries slows because of budget constraints.