Huge Amazon carbon sink is failing
If a tree falls: The Amazon rainforest has lost much of its ability to absorb climate-altering greenhouse gases from the atmosphere, scientists report.
In the 1990s, the great forest was able to store as much as 2 billion tonnes of carbon dioxide (CO ) each year, they said this week.
Now, though, the uptake has halved and, for the first time ,is being outstripped by fossil-fuel emissions from Latin America.
The evidence, reported in the journal Nature, comes from a 30-year survey that brought together nearly 100 researchers working in eight countries.
They looked at 321 forest plots, measuring 200,000 trees and recording tree deaths and growth and new trees. The scientists found a worrying surge in the rate of trees dying across the Amazon.
‘‘Tree mortality rates have increased by more than a third since the mid-1980s, and this is affecting the Amazon’s capacity to store carbon,’’ said Roel Brienen of the University of Leeds, in northern England, who led the probe.
The work runs counter to hopes that higher levels of atmospheric CO are good for ‘‘sinks’’ – the technical term for forests that soak up the principal greenhouse gas.
As CO is a key ingredient in photosynthesis, more of the gas should spur tree growth, according to this theory.
But faster growth seems to have translated into faster death.
‘‘With time, the growth stimulation feeds through the system, causing trees to live faster, and so die younger,’’ said Brienen’s colleague, Oliver Phillips.
There might be additional causes, the researchers said. Spells of drought and exceptionally high temperatures might have killed off millions of trees.
Counting on forests to be a reliable buffer against global warming was a risky assumption, the scientists said.
‘‘All across the world, even intact forests are changing,’’ said Phillips. ‘‘Forests are doing us a huge favour, but we can’t rely on them to solve the carbon problem.
‘‘Instead, deeper cuts in emissions will be required to stabilise our climate.’’