Tropical forests can get so hot that some types of leaves will not be able to photosynthesize, according to a study published in the journal Nature.
The photosynthesis mechanism in tropical trees begins to fail at an average temperature of 46.7°C. The research indicates that forests may be approaching dangerous temperature thresholds sooner than expected.
Using a combination of high-resolution data drawn from NASA’s thermal imaging instruments on the International Space Station and ground-based experiments in tropical forests around the world, the researchers found that a small fraction, about 0.01% of all foliage, is actually exposed to temperatures beyond its functional limits.
Models predict that once we hit a global temperature increase of 3.9°C, these forests could experience significant leaf damage.
Foliage warming, even if it is now in low numbers, acts as “a canary in the coal mine for tropical ecosystems,” said Chris Doughty, associate professor of environmental informatics at Northern Arizona University and the study’s principal investigator.
He said that leaf-warming experiments revealed a nonlinear rise in temperatures. “We were really surprised that when we warmed the leaves by 2, 3 or 4°C, the highest leaf temperatures went up by 8°C. This shows troubling nonlinear feedback that we weren’t expecting,” said Doughty.
“If we adopt a do-it-yourself response to climate change and increase tropical forest air temperatures by more than 4°C, there could be massive leaf death, potential tree death, and species turnover in all tropical forests,” he added.
In terms of global impact, “the photosynthetic response will be the tip of the iceberg in terms of impacts – reduced carbon uptake, potentially increased mortality and even triggering potential shifts from forests to savannas,” said Matt Disney, professor of remote sensing at UCLA. University College London.
At least 50% of global carbon dioxide2 Exchange takes place through forest canopieswhich act as the main regulators of our climate.
“The significance of this work is that it represents the first look at the specific impact of this leaf-scale warming on photosynthesis in tropical forests,” Disney said. “Although it’s quite specific, it also provides a really interesting look at one of the fundamental processes in this region, and what might happen to it in the near future if we don’t act quickly.”
Avoiding high emissions in the first place was key to achieving temperature stability. “We have to do everything we can to avoid high-emission scenarios. Under low-emission scenarios, almost all leaves of trees in tropical forests could avoid death from warming and trees would still survive,” said Simon Lewis, Professor of Global Change Science at University College London. Alive”.
“However, what the study doesn’t look at are heat waves. We still might see tree death due to warming for limited periods during heat waves under low emissions scenarios. Given that trees are so long-lived, mass death has occurred,” Lewis added. Isolating trees could have significant impacts on the rest of the plants and animals that depend on these large trees in the rainforest canopy.”
The researchers point out that the damage is not yet irreversible. “Our model projections are not destiny. It suggests that with some basic mitigation of climate change, the tropics could avoid this fate,” Doughty said. “Furthermore, it helps identify some key areas that need more research, such as Whether tropical trees can alter upper temperature thresholds.”
Disney urged people to take action. “Vote for politicians who are serious about tackling climate change and transitioning to low-carbon economies,” he said. More generally, we can all recognize the importance of supporting those countries, and the people who live in and economically depend on tropical forests, to help these transitions.
“But the serious changes to tropical forests that this work hints at don’t just affect local populations — it’s a global issue.”
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