How do trees cool the air?

The most obvious way trees cool the air is by shading. Reducing the amount of sunlight striking buildings and pavement reduces the amount of energy that is absorbed and re-radiated into the air.  

Trees also cool the air by a process known as ‘transpiration cooling‘. As trees release water into the atmosphere from their leaves via transpiration, the surrounding air is cooled as water goes from liquid to a vapor. The process is similar to evaporation pads used to cool greenhouses — except in trees, water moves into the tree’s roots from the soil and travels through the tree’s water-conducting system, eventually being transpired from the leaves.  The water that is released in its gas vapor form has a cooling effect on the surrounding air.