The most extensive land-based study of the Amazon to date reveals that the world’s vast carbon sink is losing its capacity to absorb carbon from the atmosphere because its trees are dying quickly.
By absorbing more carbon from the atmosphere than it releases, the Amazon has helped to put a brake on the rate of climate change. But that is now changing. According to lead author Dr. Roel Brienen from the University of Leeds, tree mortality rates have increased by more than a third since the mid-1980s, affecting the Amazon’s capacity to store carbon.
Initially, an increase in carbon dioxide in the atmosphere – a key ingredient for photosynthesis – led to a growth spurt for the Amazon’s trees, the researchers say. But the extra carbon appears to have had unexpected consequences. “With time, the growth stimulation feeds through the system, causing trees to live faster, and so die younger,” explains co-author Professor Oliver Phillips.
Recent droughts and unusually high temperatures in the Amazon may also be playing a role.
Their findings have an impact on climate change models that are based on continued increase of carbon storage in tropical forests, which Brienen says may be too optimistic: “Our study shows that this may not be the case and that tree mortality processes are critical in this system.”
The researchers say that we cannot rely on forests to solve our carbon problem, calling instead for deeper emissions cuts to stabilise our climate.
The study involved almost 100 scientists, many working for decades across eight countries in South America. The work was coordinated by RAINFOR, a unique research network dedicated to monitoring the Amazonian forests.
Photo credit: Peter van der Sleen