SINGAPORE The world's forests can play an even greater role in fighting climate change than previously thought, scientists say in the most comprehensive study yet on how much carbon dioxide forests absorb from the air.
The study may also boost a U.N.-backed program that aims to create a global market in carbon credits from projects that protect tropical forests. If these forests are locking away more carbon than thought, such projects could become more valuable.
Trees need large amounts of planet-warming carbon dioxide (CO2) to grow, locking away the carbon in the trunks and roots.
But scientists have struggled to figure out exactly how much CO2 forests soak up in different parts of the world and a global total for how much is released when forests are cut down and burned.
The study released on Friday in the latest issue of the U.S. journal Science details for the first time the volumes of CO2 absorbed from the atmosphere by tropical, temperate and boreal forests. The researchers found that forests soak up more than 10 percent of carbon dioxide from human activities such as burning coal, even after taking into account all of the global emissions from deforestation.
"This analysis puts forests at even a higher level of importance in regulating atmospheric CO2," said Pep Canadell, one of the authors and head of the Global Carbon Project based at the Commonwealth Scientific and Industrial Research Organization in Australia.
"If you shut them down, you're not only losing the carbon stock into the atmosphere, you're losing a very active sink which removes the carbon dioxide," he told Reuters from Canberra.
Canadell and an international research team combined data from forest inventories, models and satellites to construct a profile of forests as major regulators of atmospheric CO2.
Greenhouse gas emissions from burning fossil fuels and deforestation are rising rapidly, with growth being largely driven by surging coal, oil and gas consumption in big developing nations.
Emissions grew 5.8 percent last year to 33.16 billion tonnes, as countries rebounded from economic recession, a BP report said in June. China's emissions totaled 8.33 billion tonnes, up 10 percent from the year before.
The researchers found that in total, established forests and young regrowth forests in the tropics soaked up nearly 15 billion tonnes of CO2, or roughly half the emissions from industry, transport and other sources.
But the scientists calculated that deforestation emissions totaled 10.7 billion tonnes, underscoring that the more forests are preserved the more they can slow the pace of climate change.
A major surprise was the finding that young regrowth forests in the tropics were far better at soaking up carbon than thought, absorbing nearly 6 billion tonnes of CO2 -- about the annual greenhouse gas emissions of the United States.
"This is huge and the relevance for REDD is here you have a huge sink that is bigger than the established tropical forests," said Canadell, referring to the U.N.-backed scheme reducing emissions from deforestation and degradation.
REDD aims to reward poorer nations that preserve their carbon-rich rainforests with a market-based scheme in which carbon credits are given for every tonne of carbon locked away. Many REDD projects currently being developed focus on peat-swamp forests because these contain the most carbon.
Tropical regrowth forests could represent a new investment opportunity, Canadell said.
"Unfortunately, some countries have not looked on forest regrowth as a component of REDD, and so are missing a very important opportunity to gain even further climate benefits from the conservation of forests," he said.
(Editing by Ed Lane)