In Some Forests, Photosynthesis May Just Stop Working. It Would Be a Disaster.
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The photosynthetic machinery in tropical trees hits a critical failure point when the temperature skyrockets.
The leaves of the upper canopies in tropical rainforests suffer the most stress.
Scientists say that there’s still time to protect rainforests from a sweltering fate.
It’s not good to be a leaf in the upper canopy of tropical forests right now. It’s getting too hot for photosynthesis to work, which could have a catastrophic impact if extreme temperatures continue to sear the forests.
A new study published in the journal Nature highlights how extreme heat reaches a tipping point for photosynthesis, shutting the process down and potentially spiraling entire forests into a struggle to survive. We haven’t reached a catastrophic state yet, the authors wrote, but a few pockets of forest have already reached peak temperatures. And models are predicting that number will only increase.
“Even though a small percentage of leaves are currently doing this, our best guess is that a 4 degrees Celsius increase in temperature could cause some serious issues for certain tropical forests,” Christopher Doughty, study lead and associate professor of ecoinformatics at Northern Arizona University, said in a press conference, according to Live Science.
The study notes that the “average critical temperature” at which photosynthetic machinery in tropical trees starts to fail due to heat is 116°F. While a minuscule fraction of leaves hit this threshold currently—we’re talking just.01 percent—it doesn’t take much for that number to rise.
Currently, average peak temperatures in these regions hover around 93°F, though sections of forest have already been averaging 104°F.
According to Doughty, trends show that the air temperature bumping up just 3.6°F to 5.4°F causes the actual temperature of the leaves to jump more than 14°F. That could spell disaster for tropical forests teetering on temperature thresholds, sending waves of destruction over a lack of photosynthesis.
“While the number is small it has large implications,” Joshua Fisher, study co-author and associate professor of environmental science at Chapman University in California, said in a press conference, according to Live Science. “It’s not going to go.01 to.02. It’s going to jump nonlinearly. It’s going to increase potentially much faster.”
The team took data from the Ecosystem Spaceborne Thermal Radiometer Experiment on the International Space Station (ISS) to map the world’s tropical forest temperatures, and combined it with ground readings to reach the study’s conclusions. Then, through experiments in Brazil, Puerto Rico, and Australia, the team discovered how much hotter it needed to get to really start to impact entire forests.
And with the leaf temperature—especially in the canopy—pushing the limits of extreme heat faster than the air itself, it may not take long for us to start seeing a negative impact on the trees.
“There’s all sorts of potential feedbacks once you start losing bits of forest,” Doughty says, according to ABC.
During the photosynthesis shutdown, scientists say that the hottest portions of a tree will have their water-carrying stomata closed off, which kills them. That changes the tree’s canopy, bringing yet another layer into contact with the sweltering conditions—a potential compounding impact that could eventually wipe out entire branches and trees.
“If you have 10 percent of the leaves dying, the whole branch is going to be warmer because a critical part of that branch can no longer cool the broader branch,” Doughty said. “Likewise, you can make that assumption across the whole forest when a tree dies.”
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