Forests that today soak up a quarter of carbon pollution spewed into the atmosphere could soon become a net source of CO2 if Earth's surface warms by another two degrees Celsius (3.6 degrees Fahrenheit), cautions a report to be presented Friday at the UN.
Plants both absorb and exhale carbon dioxide, but healthy forests -- especially those in the tropics -- take up far more of the greenhouse gas than they give off.
When they are damaged, get sick or die, that stored carbon is released.
"We normally think of forests as putting the brakes on global warming," said Risto Seppala, a professor at the Finnish Forest Research Institute and head of the expert panel that produced the report.
"But in fact over the next few decades, damage induced by climate change could cause forests to release huge quantities of carbon and create a situation in which they do more to accelerate warming than slow it down."
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