Making urban roofs and pavements more reflective could cool Earth's climate slightly but measurably at little or no cost, researchers say. Altogether, urban and suburban areas between the latitudes of 45°N and 45°S—a swath that stretches from near Minneapolis, Minnesota, to south-central Chile—cover about 2 million square kilometers, an area slightly larger than Mexico. Because roofs and pavements account for more than 60% of urban surfaces (see image), using lighter-colored roofing materials (concrete versus asphalt, for example) could boost average albedo, or reflectivity, enough to drop global average temperature by as much as 0.07°C, the researchers report online today in Environmental Research Letters. Achieving the same amount of cooling by slashing carbon dioxide emissions would require taking every automobile on the planet off the road for about 50 years, the researchers estimate. Although brightening all of the roofs and pavements in every urban and suburban area worldwide sounds like a Herculean task, it could be done rather easily and relatively quickly with little added expense: Roofs are typically replaced or resurfaced every 20 to 30 years, and streets and roads are repaved every 10 years or so, with brighter alternatives often costing little or no more than the materials now in place, the researchers claim.
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