The ability of the world's tropical forests to absorb carbon from the atmosphere is decreasing - decades ahead of predictions, researchers have warned.
The finding that tropical forests are absorbing less of the extra carbon dioxide caused by human activities makes efforts to cut emissions to curb rising global temperatures even more urgent, scientists said.
Existing undisturbed tropical forests are a crucial global carbon store or "sink", which slow the impacts of emissions by removing carbon dioxide from the air and storing it in trees.
But a new study suggests a feared switch in the world's tropical forests from a carbon sink to being a source of extra carbon dioxide - putting out more of the gas from the death of trees than living trees absorb - has begun.
The study, published in the journal 'Nature', suggests the overall uptake of carbon by intact tropical forests peaked in the 1990s.