Climate change: 'Feedback' triggers could amplify peril

New studies have warned of triggers in the natural environment, including a greenhouse-gas timebomb in Siberia and Canada, that could viciously amplify global warming.

Thawing subarctic tundra could unleash billions of tonnes of gases that have been safely stored in frosty soil, while oceans and forests are becoming less able to suck carbon dioxide (CO2) out of the atmosphere, according to papers presented this weekend.

Together, these phenomena mean that more heat-trapping gases will enter the atmosphere, which in turn will stoke global warming, thrusting the machinery of climate change into higher gear.

Researchers in Finland and Russia discovered that nitrous oxide is leaking into the air from so-called "peat circle" ecosystems found throughout the tundra, a vast expanse of territory in higher latitudes.

CO2 and methane account for the lion's share of the gases that have driven global temperatures inexorably higher over the last century.

Nitrous oxide, or N2O, is far less plentiful in volume, but 300 times more potent as a greenhouse gas than CO2. It accounts for about six percent of total global warming, mainly due to a shift toward chemical-intensive agriculture.

In experiments near the Russian city of Vorkuta, Pertti Martikainen of the University of Kuopio in Finland and colleagues found that N2O leaked as a result of cryoturbation, a process that occurs when frozen soil is thawed and then refreezes.

"There is evidence that warming of the Arctic will accelerate cryoturbation, which would lead to an increased abundance of peat circles in the future," said their paper, published on Sunday in the journal Nature Geoscience.

"This would increase N20 emissions from tundra, and therefore a positive feedback to climate change."

Research presented Saturday at a meeting of the American Association for the Advancement of Science (AAAS) in Chicago suggested that the frozen soil of the tundra stored far more greenhouse gas that previously thought.

"Melting permafrost is poised to be a strong foot on the accelerator pedal of atmospheric CO2," said Chris Field, a professor at Stanford and a top scientist on the United Nation's Intergovernmental Panel for Climate Change (IPCC).

"The new estimate of the total amount of carbon that's frozen in permafrost soils in on the order of 1,000 billion (one trillion) tonnes," he said.

By comparison, the amount of CO2 that has been released through the burning of fossil fuels since the beginning of the Industrial Revolution is around 350 billion tonnes.

The greenhouse gases in the tundra, which also includes methane, come from the decayed remains of vegetation that died long ago.

Meanwhile, new research on the Southern Ocean surrounded Antarctica suggest that the sea, a vital "carbon sink," is sucking up less CO2 than before.

Nicolas Metzl, a researcher at the French National Research Institute, said fierce winds -- aggravated by climate change and gaps in the ozone layer -- were churning the sea, which brought CO2 to the surface and released it into the air.

This adds to previous research that points to the sea's drooping effectiveness as a carbon sponge, he said.

"Today, human activity injects about 10 billion tonnes of CO2 per year into the atmosphere, compared to around six billion in the early 1990s," said Metzl.

"Before we had an ocean that captured some two billion tonnes -- about a third. Today we are below two billion tonnes," less than a fifth of the total, he added.