Brian Stone : There are two reasons for the increase in urban areas . Number of heat - wave days in U.S. cities has doubled since 1950s . Stone says greenhouse gases , loss of trees and grass in cityscape are to blame . Frequency of heat waves in cities a significant public health concern , he writes . He urges planting trees , making city - reflective , better sanitation systems .
Brian Stone : Number of heat - wave days in U.S. cities has doubled since 1950s . Stone says greenhouse gases , loss of trees and grass in cityscape are to blame . Frequency of heat waves in cities a significant public health concern , he writes . He urges planting trees , making city - reflective , better sanitation systems .