How many trees does it take to cool a city?

New tool to set urban tree canopy goals. Allows urban planners and decision makers to set more specific and science-based city-wide goals for heat reduction. For Baltimore city-wide, a 1% tree canopy increase would reduce surface temperature by 32 degrees Fahrenheit. Co-author Steward Picket says "Trees are good at cooling because they pump a lot of water from the ground into the air, and when that water evaporates at the leaf surface, it absorbs a vast amount of heat. That's just the physics of evaporation. The shade provided by trees also helps with cooling." Read the article on the PHYSORG website here. Read the full study published Monday in Proceedings of the National Academy of Sciences.