Plants could become hotter faster than the surrounding air as the climate warms, increasing pressure on ecosystems and weakening their ability to absorb carbon dioxide.
Researchers warn most climate models are underestimating the impact because they focus on air temperature rather than the heat experienced by plant leaves.
A University of Arizona-led study found canopy temperatures are projected to rise around 0.11°C more than air temperatures by the end of the century, increasing the difference between the two by 16%. The research combined satellite observations with Earth system model simulations to examine how vegetation could respond under a high-emissions scenario.
Lead author Julia Green, Assistant Professor in the university’s Department of Environmental Science, said: “Plant surface temperature has a first-order impact on plant photosynthesis, transpiration, respiration and other important processes.
“Many of the researchers studying the impact of temperature on plants are using air temperature in their modeling – but our study shows that if you’re using air temperature alone, you’re going to be underestimating the temperature effects on plants.”
Leaves can become hotter than the surrounding air because they absorb direct solar radiation. Plants normally regulate this heat through transpiration, drawing water to their leaves where it evaporates and cools the surface.
However, hotter and drier conditions can force plants to conserve water by reducing transpiration and shutting down photosynthesis. This removes a key cooling mechanism and causes leaf temperatures to rise even faster, creating a feedback loop that could intensify local drying.
The study found the gap between canopy and air temperatures could increase across around 81% of vegetated regions, with the largest changes expected in arid areas. Some locations could see plant surfaces warm by up to 0.5°C more than the surrounding air by 2100.
Tropical ecosystems could also face serious risks because their plants are less accustomed to large temperature fluctuations. Even relatively small increases could affect biodiversity, vegetation distribution and the ability of forests to store carbon.
Higher plant temperatures could reduce photosynthesis, leaving more carbon dioxide in the atmosphere and potentially accelerating climate change.
Reduced transpiration could also cut the amount of moisture entering the atmosphere, affecting cloud formation and rainfall.
Prof Green said: “The more accurate our climate change models are, the more informed our decisions can be. Having a clearer picture of what could happen is necessary to create adaptation and mitigation plans that can actually be effective.”
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