Tropical forests matter to each and every one of us. They suck colossal quantities of carbon out of the atmosphere, providing a crucial brake on the rate of climate change. Yet, new research we have just published in Nature shows that intact tropical forests are removing far less carbon dioxide than they used to.
The change is staggering. Across the 1990s intact tropical forests – those unaffected by logging or fires – removed roughly 46 billion tonnes of carbon dioxide from the atmosphere. This diminished to an estimated 25 billion tonnes in the 2010s. The lost sink capacity is 21 billion tonnes of carbon dioxide, equivalent to a decade of fossil fuel emissions from the UK, Germany, France and Canada combined.
How did we reach such an alarming conclusion, and how is it that nobody knew this before? The answer is that we – along with 181 other scientists from 36 countries – have spent years tracking individual trees deep in the world’s rainforests.
The idea is simple enough: we go and identify the tree species and measure the diameter and height of every individual tree in an area of forest. Then a few years later we return to exactly the same forest and re-measure all the trees again. We can see which grew, which died and if any new trees have grown.
These measurements allow us to calculate how much carbon is stored in a forest, and how it changes over time. By repeating the measurements enough times and in enough places, we can reveal long-term trends in carbon uptake.
