SCIENCE:

IPCC expert sees greenhouse gas buildup accelerating

SAN FRANCISCO -- A leading biologist says global warming may advance faster than expected if higher temperatures start fires in the tropics and melt the Arctic tundra.

In remarks delivered in Chicago, Intergovernmental Panel on Climate Change scientist Chris Field on Saturday warned that future dry conditions in the tropics could ignite long-held carbon repositories and release tons of greenhouse gas emissions into the atmosphere.

This effect could be replicated in the Arctic, he said, where an acceleration of permafrost thawing could mean increased amounts of CO2 and methane.

"There is a real risk that human-caused climate change will accelerate the release of carbon dioxide from forest and tundra ecosystems, which have been storing a lot of carbon for thousands of years," said Field, who teaches at Stanford University and was among the group of IPCC scientists awarded the Nobel Peace Prize in 2007 along with former Vice President Al Gore.

Field's comments were delivered before the American Association for the Advancement of Science. His speech was meant to be an interim update since the IPCC's fourth assessment on the effects of climate change. A fifth assessment is upcoming.

The fourth assessment concluded that the Earth's temperature is likely to increase 2 to 11.5 degrees Fahrenheit by 2100.

'Large and destructive' fires in the tropics?

But Field said the fourth assessment underestimated the potential severity of climate change, mostly because China and India are building more and more coal-fired power plants to meet surging electric demand.

Looking ahead, of particular concern to Field are the tropics, which he said could start to ignite if higher temperatures lead to dry conditions.

"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."

Loss of tropical forests to wildfires and deforestation could lead to higher atmospheric CO2 concentrations of 10 to 100 parts per million by the end of the century, he said.

In the Arctic, Field said, the release of CO2 from decaying organic matter "that has been frozen for millennia" is a more pressing short-term concern.

"The new estimate of the total amount of carbon that's frozen in permafrost soils is on the order of 1,000 billion tons," he said. "By comparison, the total amount of CO2 that's been released in fossil fuel combustion since the beginning of the Industrial Revolution is around 350 billion tons. So the amount of carbon that's stored in these frozen soils is truly vast."

Much of this carbon is trapped in plants that have been frozen for 25,000 to 50,000 years, Field said. The frozen plants are susceptible to decomposition when the tundra thaws, making the melting of permafrost a danger.

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