As the temperature climbs, so too does the rate of evaporation. At some point the leaf closes its stomata—its mouths—and holds its breath. This stops water loss, but also halts photosynthesis, because the leaf can no longer inhale CO2. Leaves regularly stop photosynthesis during the hottest hours of the day. But rising temperatures could force them to do this more frequently and for longer periods, reducing the trees’ food supply.
