THE GUARDIAN
Tropical forests could become so hot that some kinds of leaves will no longer be able to conduct photosynthesis, according to a study published in the journal Nature.
The photosynthetic machinery in tropical trees begins to fail at about 46.7C on average. The research suggests that forests may be nearing dangerous temperature thresholds sooner than expected.
Using a combination of high-resolution data from Nasa’s thermal imaging instruments on the International Space Station and ground-based experiments in tropical forests across the world, researchers found that a small fraction, approximately 0.01% of all leaves, are already exposed to temperatures beyond their functional limits.
Models predict that once we hit a global temperature increase of 3.9 C, these forests might experience mass leaf damage.
Warming leaves, even if now in low numbers, act as a “canary in a coalmine for tropical ecosystems”, said Chris Doughty, an associate professor of ecoinformatics at Northern Arizona University and the lead researcher of the study.
He said the leaf-warming experiments had revealed a nonlinear rise in temperatures. “We were really surprised that when we warmed leaves by 2, 3 or 4C, the highest leaf temperatures actually increased by 8C. This shows a concerning nonlinear feedback that we were not expecting,” said Doughty.
“If we adopt a do-nothing response to climate change and tropical forest air temperatures increase by greater than 4C, there could be massive leaf death, possible tree mortality and species turnover across all tropical forests,” he added.
In terms of global impact, “the photosynthetic response would be the tip of the iceberg in terms of effects – reduced carbon uptake, likely increased mortality and even triggering possible transitions from forest to savannah”, said Mat Disney, a professor of remote sensing at University College London.
At least 50% of global CO2 exchange occurs through forest canopies, which act as key regulators of our climate.
“The importance of this work is that it is a first look at the specific impact of this leaf-scale warming on photosynthesis in tropical forests,” Disney said. “So while it is quite specific in one sense, it also provides a really interesting look at one of the underpinning processes in this region, and what might happen to it in the near future if we don’t act fast.”
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