The world’s tropical forests are far-flung places to most people. But they matter to our daily lives more than you think. When left intact they remove astonishing amounts of carbon dioxide from the atmosphere. They are what scientists call a natural carbon sink, slowing down the rate of climate change.
Yet our new research published in the journal Nature today shows that their ability to slow climate change is declining. Our research teams have measured 300,000 individual trees across African and Amazonian forests spanning 30 years, which highlight that the threat from climate change is more severe than we previously thought.
Our findings show that back in the 1990s intact tropical forests were absorbing 4.6 billion tonnes of carbon dioxide every year. This has slumped to an estimated 2.5 billion tonnes each year over the last decade. To put these colossal numbers in context, the decline of 2.1 billion tonnes each year is equivalent to five times the annual carbon dioxide emissions of the UK. Tropical forests have been helping us, but that help is starting to wane.
These remote forests act as a carbon sink when the amount of carbon gained through tree growth is larger than the amount lost through tree mortality. What is happening today is that tree deaths are rising as a result of periodic droughts and heat-waves.
For many decades the increasing levels of carbon dioxide in the atmosphere causing climate change increased the rate of tree growth by a process known as carbon fertilisation, but this is increasingly being outweighed by the rising negative climate change impacts causing tree deaths.
Today, standing tropical forests are still a major brake on the rate of climate change, and of course, if they are cut down and burnt then all the carbon stored in the trees is released into the atmosphere. We need to keep tropical forest standing and to urgently slow climate change if we are to avoid a grim future, where nature turns against us and forests start releasing carbon and accelerating the problem.
Stabilising tropical forest carbon stocks means stabilising the climate. To stabilise the climate requires carbon dioxide emissions to go to zero. Fast. We can still emit some carbon, but if we do, then what we emit needs to be removed from the atmosphere, so the result is net zero emissions. The good news is more and more countries are following the UK and legislating for net zero carbon emissions.
But far-off targets like “net zero in 2050” are easy to make. What the world also needs is near-term strategies including a series of concrete commitments to fund a global transition to clean energy in the lead-up to the UK convening crucial UN climate change talks in Glasgow in November, known as COP26. This will require countries to come together in a spirit of cooperation and mutual support.
Africa will be one key region. One surprising finding in our new study is how important the forests of the Congo Basin are. Despite covering a much smaller area than the Amazon they currently absorb almost as much carbon dioxide each year. The African carbon sink is proving to be more resilient to climate change than the Amazon.
This week Gabon is chairing the African Group of Climate Change Negotiators, who are clear that Africa needs its forests, as well as a clean energy revolution. And the world needs Africa’s forests: Gabon, 88% covered by rain forest, absorbs twice as much carbon dioxide than it emits.
It is vital that the world comes together at COP26 in Glasgow to agree how to implement and strengthen the Paris Agreement. We need to see emissions declining fast, by almost half by 2030, in order to avoid reaching that feared point where critical carbon sinks become carbon sources and climate change begins to run out of control.
Simon Lewis is Professor of Global Change Science at University College London, and Lee White is the government of Gabon’s Minister for Water, Forests, the Sea and Environment
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