Trees provide ultraviolet-B protection.

• Position: Climate

A method to estimate the amount of protection trees provide against ultraviolet-B radiation that may influence how communities are built and the incidence of skin cancer has been developed at Purdue University, West Lafayette, Ind. "We now have a model to predict how much UV-B radiation people receive under different amounts of tree cover," indicates agronomy professor Richard Grant. "If you're in what most people consider shade, you're still getting 40% to 60% of the UV-B exposure that would hit you in direct sunlight." Grant and his research team created a three-dimensional model that can predict how much UV-B radiation exposure exists under trees affording varying amounts of shade. The scientists then used the model to estimate how much exposure people received in residential suburban areas beneath cloud-free skies.

Experts consider UV-B to be the most-damaging part of Earth atmosphere-penetrating solar radiation, which also includes UV-A. More than 1,000,000 cases of skin cancer--either basal, squamous, or melanoma--are expected to occur in the U.S. this year, according to the Centers for Disease Control and Prevention. Several factors influence the amount of UV-B exposure. These include altitude, latitude (distance from the Equator), time of day, and amount of tree cover. The researchers used all of these elements in their calculations. At...