Plants play a vital role in combating climate change by absorbing carbon dioxide (CO₂). However, groundbreaking research warns that extreme heat could disrupt this process, potentially transforming plants from carbon absorbers into carbon emitters—a shift that might worsen global warming.
The Hidden Leak in Plant Defenses
Dr. Sean Michaletz, a botanist at the University of British Columbia, challenges longstanding assumptions about how plants lose water. While scientists previously believed plants release most water through leaf pores (stomata), which close during heatwaves to conserve moisture, Michaletz’s team discovered a critical flaw: plants increasingly lose water through their cuticle, a waxy outer layer that cannot close.
“Thinner cuticles mean more water escapes as temperatures rise,” explains Michaletz. “This forces plants to shut their pores to survive, blocking CO₂ intake and halting photosynthesis.” Without photosynthesis, plants stop absorbing CO₂ and may even release stored carbon when stressed—flipping their role in the climate system.
When Do Plants Reach Their Breaking Point?
In a study of 200 plant species, photosynthesis began failing between 40°C and 51°C. During British Columbia’s 2021 heat dome, temperatures hit 49.6°C, pushing plants to their limits. While some desert species survive up to 60°C, most plants face catastrophic cell damage beyond this threshold.
Globally, researchers warn vegetation could transition from carbon sink to source at average temperatures near 30°C—a looming risk as Earth’s current average is 16°C and rising. “Microclimates and water access might delay this shift, but we’re closer than we think,” Michaletz adds.
Lessons from Biosphere 2’s Artificial World
Michaletz’s work at Arizona’s Biosphere 2—a failed 1990s experiment to create a sealed ecosystem—highlighted how extreme heat disrupts plant function. Though the project famously faltered due to CO₂ spikes and human conflict, its rainforest biome provided critical data on temperature stress.
A Race Against Time
Plants have adapted to past climate shifts, but today’s rapid warming tests their limits. If global temperatures surge unchecked, forests could unravel into carbon emitters, triggering irreversible feedback loops. “Understanding these thresholds isn’t just academic,” says Michaletz. “It’s key to predicting whether Earth’s ecosystems will help—or hinder—our fight against climate change.”
