It has long been assumed that forests will be the "get out of jail free card" we need to help soak up spiralling carbon dioxide emissions.

Now measurements from the Smithsonian Tropical Research Institute (STRI) on Barro Colorado Island, and from other sites around the world are starting to suggest quite the opposite. Trees in these areas are starting to grow more slowly - a sign that they may already be suffering from climate change

It has long been known that warmer temperatures will stunt tree growth, but no one imagined it had already begun"

Across 18 forest plots, the dominance of quickly growing tree species increased over 20 years, while the dominance of slow-growing species decreased.

On the face of it, this sounds like a good thing. However, fast-growing trees produce wood that is up to 60 per cent less dense than in some slow growers. So a major shift from slowly to quickly growing trees across the Amazon could drastically reduce the carbon stored in wood.