Trees have long been held up as potential saviors for our overheating planet. As we overload the air with carbon pollution that traps heat, it's tempting to think our great green arboreal allies will come to the rescue despite flaws in that logic.
Too much pollution? Plant more trees. Need to save the world? Rainforests can do it — or so the thinking goes. Trees live by soaking up carbon, after all.
However, new research on the failure of tropical photosynthesis at high temperatures suggests these solutions are becoming less clear-cut.
What's happening?
Trees in tropical forests may, sooner than expected, reach critical temperatures at which they begin to fail to effectively take in carbon dioxide (and water) while outputting oxygen (and sugar), the Guardian wrote based on a paper published in the journal Nature in August.
"Tropical forests could become so hot that some kinds of leaves will no longer be able to conduct photosynthesis," the Guardian summarized.
To study current leaf temperatures, the scientists paired thermal imaging from NASA equipment on the International Space Station with on-the-ground experiments.
They found that leaves in forests' upper canopies were already above a threshold temperature for affecting photosynthesis about 0.01% of the time.
The researchers predicted that, based on models, forests might withstand up to about a 7-degree Fahrenheit increase in air temperature.
Why is a failure of photosynthesis in the tropics concerning?
Researchers noted that a 7-degree increase is "within the 'worst-case scenario'" predictions of how much tropical temperatures could rise — barely.
"If we adopt a do-nothing response to climate change, and tropical forest air temperatures increase by [more than 7.2 degrees], there could be massive leaf death, possible tree mortality, and species turnover across all tropical forests," Chris Doughty, the study's lead researcher, told the Guardian.
Even if trees survived but lost leaves, the world could lose a major carbon stabilizer, potentially worsening the overheating.
"The photosynthetic response would be the tip of the iceberg in terms of effects [including] reduced carbon uptake, likely increased mortality, and even … possible transitions from forest to savannah," Mat Disney, a University College London professor not involved in the study, told the Guardian.
What can I do to help tropical trees?
Disney suggested people take action: "Vote for politicians who are serious about addressing climate change and transitioning to low-carbon economies," he told the Guardian, adding that "we can all recognize the importance of supporting those countries and people who live in and rely on tropical forests."
The research paper rang a hopeful note: "It is still within our power to decide … the fate of these critical realms of carbon, water, and biodiversity."
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