Tropical forests may be getting too hot for photosynthesis

A small percentage of leaves on trees in tropical forests may be approaching the maximum temperature threshold for photosynthesis to work, suggests a study published in Nature. “The 4 degree C estimate is within the ‘worst-case scenario’ of climate change predictions for tropical forests and therefore it is still within our power to decide the fate of these critical realms of carbon, water and biodiversity,” the authors write. “The combination of climate change and local deforestation may already be placing the hottest tropical forest regions close to, or even beyond, a critical thermal threshold” they add. “Therefore, our results suggest that the combination of ambitious climate change mitigation goals and reduced deforestation can ensure that these important realms of carbon, water and biodiversity stay below thermally critical thresholds.” Tropical forests serve as critical carbon stores and host most of the world’s biodiversity and may be particularly sensitive to increasing temperatures. The critical temperature beyond which photosynthetic machinery in tropical trees begins to fail averages at about 46.7 degrees C. However, whether leaf temperatures experienced by tropical vegetation approach this threshold, or soon will under climate change, remains unclear.