San Gabriel Valley

NO SWEAT: After months of measuring environmental moisture and air temperatures, researchers reached a disappointing conclusion about the relationship between greenery and humans: Tree sweat doesn’t cool people off.

The study, conducted during the summers of 1993 and 1994, was expected to find that the moisture given off by trees--called transpiration--acts as a communitywide air conditioner. With that in mind, Indiana University climatologist Sue Grimmond and U.S. Forest Service researchers measured temperatures and humidity in a tree-lined Arcadia neighborhood and in a building-packed area near the San Gabriel Mission.

The idea behind the study was that much as perspiration cools humans, the gallons of water given off by trees might allow an entire neighborhood to turn air conditioners down a bit--which was why Rosemead-based Southern California Edison Co. funded the study. But results of the experiment indicate that trees don’t cool neighborhoods and might in fact warm them slightly.

Temperatures in the greener area turned out to be equal to or up to 1 degree warmer than the asphalt-dominated area.