Scientists worldwide are watching temperatures rise, the land turn dry and vast forests go up in flames.
In the Siberian taiga and Canadian Rockies, in southern California and Australia, researchers find growing evidence tying an upsurge in wildfires to climate change, an impact long predicted by global-warming forecasters.
A team at California's Scripps Institution, in a headline-making report this month, found that warmer temperatures, causing earlier snow runoff and consequently drier summer conditions, were the key factor in an explosion of big wildfires in the U.S. West over three decades, including fires now rampaging east of Los Angeles.
Researchers previously reached similar conclusions in Canada, where fire is destroying an average 6.4 million acres a year, compared with 2.5 million in the early 1970s. And an upcoming U.S.-Russian-Canadian scientific paper points to links between warming and wildfires in Siberia, where 2006 already qualifies as an extreme fire season, sixth in the past eight years. Far to the south in drought-stricken Australia, meanwhile, 2005 was the hottest year on record, and the dangerous bushfire season is growing longer.
"Temperature increases are intimately linked with increases in area burned in Canada, and I would expect the same worldwide,"said Mike Flannigan, a veteran Canadian Forest Service researcher.
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Nadezda M. Tchebakova, a climatologist at Russia's Sukachev Institute of Forestry, said southern Siberia's average winter temperatures in the 1980-2000 period were 2 to 4 degrees Celsius (3.6 to 7.2 degrees Fahrenheit) warmer than the pre-1960 norm.
"Snowmelt starts much earlier in the spring,"she said by telephone from the Siberian city of Krasnoyarsk."Precipitation is decreasing. This combination of elevated temperatures and decreased precipitation should provide conditions for greater fire occurrence."
As she spoke, newly ignited blazes raced through the conifer forests of Evenkiya, a summer fishing and hunting region north of Krasnoyarsk.
The Sukachev institute's satellite data show that more than 29 million acres _ an area the size of Pennsylvania _ have been burned in Russia already this year. Orbiting cameras see a red-and-green checkerboard in Siberia, of"hotspots"among endless evergreens.
The Intergovernmental Panel on Climate Change, an authoritative U.N.-sponsored network of scientists, has long predicted that summer drying and droughts would worsen forest fires, which in many regions are primarily set by humans.
Global temperatures rose an average 1 degree Fahrenheit in the 20th century, and warming will continue as long as manmade"greenhouse gases,"mostly carbon dioxide from fossil-fuel burning, accumulate in the atmosphere, the panel says.
"The change is much more rapid than initially forecast 10 or 15 years ago,"Brian Stocks, a retired Canadian Forest Service scientist, said of the fires."It seems people are finally beginning to take a look at it."
The Scripps study, in the journal Science, was unique in collating detailed data from 34 years of U.S. western wildfires with temperature, snowmelt and streamflow records. Wildfire frequency varies widely from year to year, but the California researchers found a clear trend: The average number of large fires almost quadrupled between the first and second halves of that period.
They also looked at land-use changes and forest management practices, but concluded they were secondary factors in the upsurge of fires. There were"many more wildfires burning in hotter than in cooler years,"they reported.
Such detailed data don't exist on a global scale. Doing a similar study in Russia would be difficult because Soviet-era records are unreliable. And specialists caution that wildfires remain complex phenomena. In many regions, slash-and-burn farmers, arsonists and others start most fires, and fire professionals say modifying human behavior is key.
But although humans are the prime cause,"coupled with climate change, things are becoming worse,"said Johann Goldammer, director of the Global Fire Monitoring Center at Germany's Freiburg University.
A nonhuman cause, meanwhile, may be on the rise. Warming in high northern latitudes is expected to generate more lightning, igniting more forest fires, notes the report by Amber J. Soja of the U.S. National Institute of Aerospace, Tchebakova and other U.S., Russian and Canadian scientists.
Their paper, upcoming in the U.S. journal Global and Planetary Change, looks at how current reality compares with still other effects of climate change previously foreseen for northern, boreal regions _ Siberia, Canada, Alaska.
"The forest in Siberia is shifting northward, and the forest-steppe (mixed forest and plain) is replacing it in the south,"Tchebakova said."Those were the predictions."
In Alaska, the international team found a decline in growth of white spruce trees and a spread of forest insect infestation _ also both predicted in computerized climate-change scenarios.
Goldammer pointed out that boreal forests may be crucially linked to the fate of the global environment, since the forests and their peat soils hold about one-third of Earth's stored carbon.
Forest and peat fires release carbon dioxide into the atmosphere, adding to climate warming, which in turn will intensify forest fires, further worsening warming in a planetary feedback loop.
"This is a carbon bomb,"Goldammer said of the northern forest."It's sitting there waiting to be ignited, and there is already ignition going on."
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