urbanheatisland

GLOBAL WARMING – URBAN HEAT ISLANDS

About half the global population lives in urban areas. This figure is expected to rise in the near future, reaching approximately 70 % by the year 2030. Among other things this will lead to a dramatic increase of built-up areas in towns and cities and the respective decrease of natural areas. It is these natural areas and the vegetation that collect solar radiation (photosynthesis) and produce shade,
which contributes to the reduction of heat release in cities. The decrease of large green areas also reduces atmospheric cooling. Built-up areas on the other hand
mainly consist of non-reflecting and water-resistant materials which release a signifi cant portion of the sunlight as heat, thus creating the so-called. „Urban
Heat Islands“.

URBAN HEAT ISLANDS

Cities are heat islands: at present the average annual temperature in cities is already between one and three degrees Celsius higher than in the surrounding areas. This so-called „urban heat effect“ is caused by the sun, which particularly heats up dark buildings and streets during the day. In the night this heat is only slowly released again, so that around the clock it is significantly warmer within the city than outside of urban areas.

GREENING OR REFLECTING

As early as October 2008, the American Environmental Protection Agency (EPA) issued a compendium of short-, medium- and long-term options to counteract further global warming titled „Reducing Urban Heat Islands”. Among other things, various possibilities of cooling the roofs of buildings are described and a general distinction is made between „Cool (reflecting) Roofs“ and „Green Roofs“. Cool Roofs are characterized by good reflective properties and low heat storage.

COOL ROOFS

Calculations by the American Department of Energy showed that large quantities of energy could be saved if all roofs all over the world were painted white. Whereas dark roofs only reflect 20 % of the sunlight, white roofs reflect signifi cantly more radiation back into space: buildings would require less air conditioning and vast quantities of carbon dioxide could be saved – an amount equal to the emissions by all the cars in the world in eleven years.

WHITE ROOFS REDUCE THE HEAT OF THE CITY

Meanwhile a team of scientists around Keith Oleson of the National Center for Atmospheric Research (NCAR) has established the effect of light-coloured paint on the climate. Alongside studying the effects on world climate, particular focus was also put on the climate of cities. “Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat,“ writes Oleson. „It remains to be seen if it is actually feasible for cities to paint their roofs white, but the idea certainly warrants further investigation.”

santorini