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.

earlier related report
Climate change could be even worse than feared
It seems the dire warnings about future devastation sparked by global warming have not been dire enough, top climate scientists warned Saturday.

It has been just over a year since the Nobel-winning Intergovernmental Panel on Climate Change (IPCC) published a landmark report warning of rising sea levels, expanding deserts, more intense storms and the extinction of up to 30 percent of plant and animal species.

But recent climate studies suggest that report significantly underestimates the potential severity of global warming over the next 100 years, a senior member of the panel warned.

"We are basically looking now at a future climate that is beyond anything that we've considered seriously in climate policy," said Chris Field, who was a coordinating lead author of the report.

"Without effective action, climate change is going to be larger and more difficult to deal with than we thought."

Fresh data has shown that greenhouse gas emissions have grown by an average of 3.5 percent a year from 2000 to 2007, Field told reporters at a meeting of the American Association for the Advancement of Science.

That's "far more rapid than we expected" and more than three times the 0.9 growth rate in the 1990's, he said.

While increased economic activity could have contributed to the growth in emissions, Field said it appears as though the bulk of the growth is "because developing countries like China and India saw a huge upsurge in electric power generation, almost all of it based on coal."

Further complicating the problem is that higher temperatures could thaw the Arctic tundra and ignite tropical forests, potentially releasing billions of tons of carbon dioxide that has been stored for thousands of years.

That could raise temperatures even more and create "a vicious cycle that could spiral out of control by the end of the century."

"We don't want to cross a critical threshold where this massive release of carbon starts to run on autopilot," said Field, a professor of biology and of environmental Earth system science at Stanford University.

The amount of carbon that could be released is staggering.

Since the beginning of the Industrial Revolution an estimated 350 billion tonnes of carbon dioxide (CO2) have been released through the burning of fossil fuels.

The new estimate of the amount of carbon stored in the Arctic's permafrost soils is around 1,000 billion tonnes. And the Arctic is warming faster than any other part of the globe.

Several recent climate models have estimated that the loss of tropical rainforests to wildfires, deforestation and other causes could increase the concentration of carbon dioxide in the atmosphere from 10 to 100 parts per million by the end of the century.

The current level is about 380 parts per million.

"Tropical forests are essentially inflammable," Field said. "You couldn't get a fire to burn there if you tried. But if they dry out just a little bit, the result can be very large and destructive wildfires."

Recent studies have also shown that global warming is reducing the ocean's ability to absorb carbon by altering wind patterns in the Southern Ocean. Faster winds blow surface out of the way, causing water with higher concentrations of carbon dioxide to rise to the surface.

Sea levels are also rising faster than previously estimated as ocean temperatures warm and melting ice in mountain glaciers and at the poles flows into the ocean, warned Anny Cazenave, of France's Centre National d'Etudes Spatiales.

Fresh analysis using satellite imaging has shown that in the past 16 years, average sea levels have risen at a rate that is twice as fast as the last century: more than three millimeters a year.

Some regions have seen levels rise as much as one centimeter a year, Cazenave told reporters.

The expanding use of biofuels could also contribute to global warming because farmers are cutting down and burning down tropical forests to plant crops, said Holly Gibbs of Stanford University.

"If we run our cars on biofuels produced in the tropics, chances will be good that we are effectively burning rainforests in our gas tanks," she warned.