Heat waves push tropical forests past photosynthesis limits across 57 million hectares

On July 9, 2026, a new study from Ecole Polytechnique Federale de Lausanne reveals that heat waves are pushing tropical forests beyond their photosynthesis limits, affecting over 57 million hectares. This alarming trend threatens the forests' ability to absorb carbon dioxide and could have severe implications for global warming.

Critical temperatures and photosynthesis

As temperatures rise, trees face a critical threshold for photosynthesis, the process by which they produce nutrients and oxygen while absorbing CO₂. According to Charlotte Grossiord, a lead researcher, plants possess a safety margin of about 15°. However, due to ongoing global warming and extreme weather events, this margin is rapidly diminishing.

The study, published in the Proceedings of the National Academy of Sciences, combines species-specific thermal thresholds with satellite observations to assess the extent of heat stress affecting tropical forests. As a result, trees' ability to perform photosynthesis declines, leading to reduced growth and increased mortality rates.

Impacts on biodiversity and ecosystem resilience

The consequences of rising temperatures extend beyond individual plant species. Changes in forest composition can disrupt ecosystem functions, leading to reduced animal biodiversity and weakened resilience against future heat waves and droughts. As tropical forests are vital carbon sinks, their declining capacity to absorb CO₂ could accelerate global warming.

• 43 million hectares: Area of tropical forest exceeding critical temperatures in 2001
• 57 million hectares: Current area affected as of 2026
• 83 million hectares: Expected area by 2050
• 160 million hectares: Projected area by the end of the century

Alongside these changes, tropical forests will also release less water vapor, increasing the risk of droughts and extreme weather events worldwide.

Future research and adaptation strategies

Although the study primarily focuses on tropical forests, the impacts of heat waves are also evident in regions like Switzerland, where local trees and crops are similarly affected. The methodology developed by Grossiord and her team could be crucial for identifying plants under thermal stress and determining necessary intervention measures such as irrigation.

Future studies aim to expand the range of species analyzed beyond the 200 species currently included. Understanding how rare species contribute to ecosystem functions is essential, as these species can play disproportionately important roles. Researchers also plan to extend their investigation to other regions, particularly in Europe, where heat waves have severely impacted Mediterranean forests.