The mighty Amazon rainforest is rapidly losing its ability to absorb carbon from the atmosphere, a major study has shown.
Since the 1990s, when two billion tons of carbon dioxide greenhouse gas were removed from the atmosphere each year by the forest, net uptake has halved, said scientists.
For the first time, the rate of carbon absorption by the Amazon is being overtaken by fossil fuel emissions in Latin America.
Trees dying younger as a result of soaking up too much carbon is to blame for the trend, experts believe.
Lead scientist Roel Brienen, from the School of Geography at the University of Leeds, said: “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.”
The findings are from a 30-year survey of the Amazon by an international team of almost 100 researchers − the most extensive land-based study of the forest ever conducted.
Forests are doing us a huge favour, but we can’t rely on them to solve the carbon problem
It revealed a huge surge in the rate of trees dying across the Amazon, which historically has acted as a vital ‘carbon sink’ putting a brake on climate change.
Plants depend on carbon dioxide for photosynthesis and initially increasing levels of the gas in the atmosphere led to a growth spurt in the Amazon, said the researchers. But the extra carbon appears to have had an unexpected and unwelcome side effect.
Co-author Oliver Phillips, said: “With time, the growth stimulation feeds through the system, causing trees to live faster and so die younger.”
Recent droughts and unusually high temperatures in the Amazon may also be playing a role. The study found that apart from the effects of carbon, drought has killed millions of trees.
Brienen added: “Regardless of the causes behind the increase in tree mortality, this study shows that predictions of a continuing increase of carbon storage in tropical forests may be too optimistic.
“Climate change models that include vegetation responses assume that as long as carbon dioxide levels keep increasing, then the Amazon will continue to accumulate carbon.”
The study, published in the journal Nature, involved the long-term monitoring of 321 forest plots across the Amazon’s six million square kilometres. Scientists identified and measured 200,000 trees, recording tree deaths as well as new growth since the 1980s.
Phillips said: “All across the world even intact forests are changing. 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.”