Since measurements began in 1959, night-time temperatures in the tropics have had a strong influence over year-to-year shifts in the land's carbon-storage capacity or "sink".

Earth's ecosystems absorb about a quarter of carbon from the atmosphere, and tropical forests account for about one-third of land-based plant productivity.

During the past 50 years, the land-based carbon sink's "interannual variability" has grown by 50 to 100 percent, the researchers found. "When you heat up a system, biological processes tend to increase.

At hotter temperatures, plant respiration rates go up and this is what's happening during hot nights. Plants lose a lot more carbon than they would during cooler nights," explained associate research scholar William Anderegg.

This suggests that tropical ecosystems might be more vulnerable to climate change than previously thought, risking crossing the threshold from a carbon sink to a carbon source," Anderegg added in a paper appeared in the journal Proceedings of the National Academy of Sciences.


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