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Field said that if the tropics became dry enough for fires to break out, tropical forests would pass a "tipping point" from absorbing carbon dioxide from the atmosphere to releasing it. "Tropical forests are essentially inflammable. You couldn't get a fire to burn there if you tried. But if they dry out just a little, the result can be very large and destructive wildfires. It is increasingly clear that as you produce a warmer world, lots of forested areas that had been acting as carbon sinks could be converted to carbon sources," he said. The result could lead to runaway warming.

The wildfires blazing through North Myrtle Beach, S.C., today are hardly an anomaly in a warming world. According to a landmark report that will be published tomorrow in Science, fires are not just a result of a changing climate, they're also contributing to the overall warming trend much more than imagined, the authors report. As vegetation burns, it releases stored-up carbon into the atmosphere, speeding global warming and thereby exacerbating conditions that may generate a greater incidence of wildfires in the coming years.

"What Australia showed us is that things can happen faster than we think," said study co-author Katharine Hayhoe, an atmospheric scientist and associate professor of geosciences at Texas Tech University. "Although we cannot say whether climate change played a role in the February fires in Australia, we do know that climate change will increase the risk of conditions conducive to such devastating wildfires in the near future."

Scientists have been warning for years that climate change will bring higher temperatures and lower rainfall to Australia, increasing the likelihood of deadly wildfires. Some questioned whether Saturday's fire was a sign of things to come. "It's a sobering reminder of the need for this nation and the whole world to act and put at a priority our need to tackle climate change," said Bob Brown, the leader of Australia's minor Greens Party.

Holdren said temperatures should be kept from rising more than 3.6 degrees. To get there, he said the U.S. and other industrial nations have to begin permanent dramatic cuts in carbon dioxide pollution by 2015, with developing countries following suit within a decade. Those efforts are racing against three tipping points he cited: Earth could be as close as six years away from the loss of Arctic summer sea ice, he said, and that has the potential of altering the climate in unforeseen ways. Other elements that could dramatically speed up climate change include the release of frozen methane from thawing permafrost in Siberia, and more and bigger wildfires worldwide.

From Colorado to Washington state, an unprecedented, years-long epidemic of mountain pine beetle has killed 2.6 million hectares (6.5 million acres) of forest. The insect has struck even more devastatingly to the north, in British Columbia, where clouds of beetles have laid waste to 14 million hectares (35 million acres) - twice the area of Ireland. It is expected to kill 80 percent of the Canadian province's lodgepole pines before it's finished. Farther north, in the Yukon, the pine beetle isn't endemic - yet. Here it's the spruce bark beetle that has eaten its way through 400,000 hectares (1 million acres) of woodland, and even more in neighboring Alaska, in a 15-year-old epidemic unmatched in its longevity and extent.