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 per cent 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 now have data showing that from 2000 to 2007, greenhouse gas emissions increased far more rapidly than we expected," said Chris Field, who was a co-ordinating lead author of the report.
This is "primarily because developing countries like China and India saw a huge upsurge in electric power generation, almost all of it based on coal," Field said in a statement ahead of a presentation to the American Association for the Advancement of Science.
Without decisive action to slow global warming, higher temperatures could ignite tropical forests and thaw the Arctic tundra, 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 and estimated 350 billions tons of carbon dioxide (CO2) has 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 tons. 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 store carbon by altering wind patterns in the Southern Ocean.
"As the Earth warms, it generates faster winds over the oceans surrounding Antarctica," Field explained.
"These winds essentially blow the surface water out of the way, allowing water with higher concentrations of CO2 to rise to the surface. This higher-CO2 water is closer to CO2-saturated, so it takes up less carbon dioxide from the atmosphere."
Field is co-chair of the group charged with assessing the impacts of climate change on social, economic and natural systems for the IPCC's fifth assessment due in 2014.
The 2007 fourth assessment presented at a "very conservative range of climate outcomes" but the next report will "include futures with a lot more warming," Field said.
"We now know that, without effective action, climate change is going to be larger and more difficult to deal with than we thought."
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