Atlanta , Georgia ( CNN ) -- Extreme heat in major U.S. cities this week signals more than the arrival of the dog days of summer . City dwellers have long endured hot summer afternoons , but the frequency of extremely hot days -- when admissions to hospital emergency rooms for heat-related illnesses spike -- has increased substantially over the past several decades . An analysis of weather records at Georgia Tech reveals that the average number of heat-wave days in large U.S. cities each year had increased from nine in the mid-1950s to 19 by the mid-2000s . The news is even worse for the country 's most sprawling cities , such as Atlanta , Georgia ; Tampa , Florida ; and Raleigh , North Carolina : The number of heat-wave days in these cities has nearly tripled during the same time . There are two reasons for the increase in urban areas . First , temperatures in cities are rising because of the global greenhouse effect , which is intensifying as the vehicles we drive and the energy we consume emit more and more greenhouse gases . Second , and more important , cities are warming because of the loss of trees and other natural land cover to make way for buildings , streets , and parking lots , which are composed of materials that absorb far more thermal radiation than the natural landscape . Because of these two effects -- one global , the other local -- most large American cities are warming at more than twice the rate of their outlying rural areas and the planet as a whole , and this accelerated pace is at the root of the increasing frequency of heat waves . Much more than a source of discomfort , the growing frequency of heat waves in cities poses a significant public health threat . This was made clear by an intense and prolonged heat wave in Europe during the summer of 2003 , when it 's estimated more than 70,000 residents of France , Italy , Great Britain and other nations died from exposure to extreme heat . The majority of people who died lived in cities . With a death toll exceeding that of any other weather-related natural disaster in the developed world -- including hurricanes , tornadoes and floods -- the European heat wave attests to the growing risk of climate-related health threats , even in the most affluent and medically advanced societies . Yet the global response to this climate event -- one that reveals more about the profoundly changing environment in which we live than any other yet endured -- has largely been one of indifference . Less than a decade after the deadly heat wave , many outside of Europe do not even recall hearing of it . And fewer appreciate its central lesson : The extremity of the heat was greatly amplified and so made more dangerous by the cities themselves . So , as cities prepare over the coming days for the potential health impacts of a heat wave , it is imperative that urban governments look ahead and take aggressive action over the coming years to address the root causes of rising temperatures in cities . The good news is that cities do n't have to wait for the U.S. Congress or the global community to adopt highly effective programs . Programs already under way in New York , Los Angeles and other cities to plant millions of trees can measurably cool the air and dampen the extremity of heat waves over time . The preservation and restoration of greenspaces within and around urban areas are a critical first line of defense against climate change . Coupled with enhancing greenspace is the need to make built surfaces more highly reflective , to offset the absorption of solar energy . The use of lightly hued or whitewashed roofing and paving materials , as found in Mediterranean cities , is a proven tool for moderating summer temperatures . Finally , a long-term transition from sprawl and highways toward more compact urban development , featuring walkable neighborhoods and transit systems , can reduce the emission of waste heat from vehicles and buildings . This summer shows climate change is neither a theoretical problem nor one to be addressed by future generations : It is on display this week in major U.S. cities . The opinions expressed in this commentary are solely those of Brian Stone .
Brian Stone : Number of heat-wave days in U.S. cities has doubled since 1950s . Stone says greenhouse effect , loss of trees and grass in cityscape are to blame . Comment: He urges planting greenery , making city surfaces reflective , better transit systems .