Frozen CO2, methane a time bomb: experts

Massive volumes of carbon dioxide and methane frozen in the earth's soils are a "time-bomb ticking under our feet", soil scientists say.

The thawing of vast areas of frozen soils and the decay of peatlands under higher global temperatures could release massive volumes of carbon dioxide and methane into the atmosphere - potentially doubling the amount of atmospheric greenhouse gases.

The World Congress of Soil Scientists in Brisbane has been told that frozen soils and peatlands in the northern hemisphere are estimated to store up to 50 per cent of the world's organic soil carbon.

University of Wisconsin-Madison soil scientist Dr James Bockheim said global warming threatens to thaw these soils, some of which have been frozen for thousands of years.

"Atmospheric temperatures have increased by 3 (degrees) C over the past decades in the Arctic and Antarctic regions and this continued warming may cause carbon stored in the surface permafrost to be released to the atmosphere as carbon dioxide," he said.

The potential release of greenhouse gases from frozen soils is not currently taken into account in the Intergovernmental Panel on Climate Change (IPCC) calculations as it is not known exactly how thawing will impact on greenhouse gas emissions.

Rising global temperatures will also increase decomposition of old carbon stored in peatlands, many of which also are underlain by permafrost.

Dr Merritt Turetsky, from the University of Guelph in Canada, is studying peatlands and describes them as a time-bomb ticking under our feet.

"Peatlands represent only 1-3 per cent of the world's land surface, but play a major role in the global carbon cycle," Dr Turetsky said.

"Peatlands have served as a long-term sink of carbon dioxide but today also represent one of the largest natural sources of methane.

Dr Turetsky said that, under climate change, northern regions are also becoming more vulnerable to large-scale disturbances such as fire.

Fires in remote northern regions can burn hundreds of thousands of hectares over several months, and Dr Turetsky's research has shown that when fires burn into peatlands, emissions of carbon and toxic metals such as mercury can surpass industrial levels.