If forests absorb less CO2, then effects of climate change will be worse than past models had predicted
By Chris Arsenault
ROME, July 30 (Thomson Reuters Foundation) - The world's forests are taking longer than expected to recover from increasingly frequent droughts, meaning their ability to store climate-changing carbon dioxide is smaller than previously thought, Utah University researchers said on Thursday.
If forests are absorbing less carbon dioxide, then the effects of climate change will be worse than past models had predicted, the Utah study published in the journal Science said.
"This really matters because in the future droughts are expected to increase in frequency and severity due to climate change," William Anderegg, the study's lead author, said in a statement.
"Some forests could be in a race to recover before the next drought strikes."
The Utah study showed that trees took an average of two to four years after the end of a drought to return to normal growth rates and store greater amounts of carbon dioxide.
Trees grew nine percent more slowly than expected during the first year of post-drought recovery, and five percent slower in the second year, the scientists said.
Multiplied across the world's forests, and considering the increasing frequency of droughts, these seemingly small figures have a major impact on how much carbon dioxide stays in the atmosphere.
Over a century, reduced carbon storage capacity in forests in semi-arid regions results in an extra 1.6 million gigatonnes of carbon dioxide - more than all energy-related CO2 emissions produced annually in the United States - entering the atmosphere, the study showed.
The scientists studied 1,300 forest sites worldwide using data on severe droughts beginning in 1948.
In the western United States, for example, scientists expect more frequent and more severe droughts due to climate change, which will substantially reduce forests' ability to remove carbon from the atmosphere, accelerating global warming.
"In most of our current models of ecosystems and climate, drought effects on forests switch on and off like a light. When drought conditions go away, the models assume a forest's recovery is complete and close to immediate," Anderegg said.
"That's not how the real world works."
(Reporting By Chris Arsenault, editing by Tim Pearce. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, corruption and climate change. Visit www.trust.org)
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