According to the study, photosynthesis in tropical trees begins to fail at about 46.7 degrees C (116 degrees F)

In a typical year, only around 0.01 percent of the leaves in the upper canopies surpass the temperature at which photosynthesis starts to fail. The global temperature increase that is associated with these changes is around 4 degree Celsius, which is currently in line with worst-case scenario projections.