By Adam Vaughan
Forests in the Amazon are losing the ability to absorb carbon
Amazon rainforest, Ecuador
Scientists have warned the world will have to reduce carbon emissions to net zero sooner than 2050, after they found that tropical forests are losing their ability to remove CO2 from the atmosphere.
Climate change models predict that forests in Africa and the Amazon will act as a sink for carbon emissions well into the second half of this century, but now Simon Lewis at the University of Leeds, UK and his colleagues have found that the Amazon could flip into a net emitter of carbon in as little as 15 years.
Its grim, so grim. Its the most worrying paper Ive written, says Lewis.
The team looked at ground surveys of 300,000 trees over 30 years in the two regions and found that CO2 absorption in the Amazon has already shrunk significantly, with Africa set to follow.
Intact forests across the regions removed just 6 per cent of humanitys CO2 emissions in the 2010s, or around 25 billion tonnes of CO2. In the 1990s, when the carbon sink was found to be at its peak, they removed around 17 per cent. The change was down to forests shrinking, the remaining trees growing less and so absorbing less CO2, and huge growth in human emissions.
Using these observations to model the future, the team found the Amazon could become a source of carbon by 2035. The tipping point for Africa was far enough in the future that the researchers did not project a date, but by 2030 its sink is expected to be 14 per cent lower than 2010-15.
Globally, the amount of humanitys CO2 emissions removed by forests is actually increasing, because higher CO2 concentrations and temperatures have led to more tree growth in temperate regions which, for now, has offset losses in the tropics.
In recent years, there have been growing calls to cut global emissions to net zero by 2050 to avoid temperature rises of more than 1.5°C. But this deadline is based on climate models that assume tropical forests will remain a carbon sink in the second half of this century. As that no longer appears likely, Lewis says we will need faster and greater cuts to get to net zero sooner than 2050.
Stopping deforestation, which has exploded to a 10-year high in Brazil, will also be key, because disrupted forests have more chance of drying out and releasing CO2.
Erika Berengeur at the University of Oxford, who was not involved in the analysis, says it provides a good estimate of tropical forests carbon sinks, but their diminished capability to absorb CO2 should not be used as an excuse to chop them down.
She notes the study only focuses on intact forests and points out that even though large areas of the Amazon forest have been disturbed by human activities, those parts still play a vital role in absorbing CO2.
Journal reference: Nature, DOI: 10.1038/s41586-020-2035-0
Sign up to our free Fix the Planet newsletter to get a weekly dose of climate optimism delivered straight to your inbox
More on these topics:
By Adam Vaughan