NEW YORK, April 16 (Reuters) - The world's forests are at risk of becoming a source of planet-warming emissions instead of soaking them up like a sponge unless greenhouse gases are controlled, scientists said.
Deforestation emits 20 percent of the world's carbon dioxide when people cut and burn trees, but standing forests soak up 25 percent of the emissions.
If the Earth heats up 2.5 degrees Celsius (4.5 degrees F) or more, evaporation from the additional heat would lead to severe droughts and heat waves that could kill wide swaths of trees in the tropics of Africa, southern Asia and South America. And emissions from the rotting trees would make forests a source of global warming.
"If temperatures are growing at the current pace definitely this would happen at the end of this century or before," said Risto Seppala, chair of a report by the International Union of Forest Research Organizations, a nonprofit network of scientists.
The IUFRO will present the report to the U.N.'s Forum on Forests in New York next week.
Not all areas of the world would suffer immediately and pine forests in northern parts of the world could benefit at first.
"In the beginning it would mean some very positive consequences," for boreal forests such as those found in Northern Europe and Canada, said Seppala by telephone from his home in Finland north of the Arctic Circle. He said timber and paper industries in the North could prosper as warmer weather pushes growth of spruce and other trees.
Even forests found in more temperate parts of the world, such as the United States and Western Europe, could grow faster at first.
"Those who live in industrialized countries in the Northern Hemisphere won't suffer too much at first," he said.
People in many developing countries with forests tend to rely more on forests for food, clean water and other basic needs.
But eventually tree pests and parasites that until now have not appeared much in forests in colder parts of the world are likely to spread north as temperatures warm, the report said.
An example of pests already moving to the North is the pine beetle, which has devastated large parts of forests in British Columbia over the past decade and has moved into the province of Alberta. The pest can be killed by periods of extreme cold, but the 2007-2008 winter did not kill off the insects in Alberta.
Much depends on exactly how much temperatures will warm. A Reuters poll earlier this month of scientists showed that global warming is like to overshoot a 2 degrees Celsius (3.6 F) rise above pre-industrial levels seen by many countries as the maximum to avoid the worst of rising sea levels, floods, droughts and heat waves. Temperatures have already risen 0.7 Celsius. See [ID:nL7444674 ]
Steps can be taken to protect forests and help them adapt to warmer temperatures, such as sustainable harvesting, the IUFRO report said. Perhaps even more important is cutting global emissions of greenhouse gases, said Seppala. (Editing by Christian Wiessner)
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