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Increasing the ability of urban roofs and pavements to reflect the Sun's heat would decrease the average global temperature by less than 0.1 °C over the next 300 years, according to climate simulations.
Hashem Akbari and his colleagues at Concordia University in Montreal, Canada, used a global climate model, along with estimates of the extent of the world's urban areas, to predict what would happen if urban solar reflectivity rose from roughly 15% to 25%. Depending on which set of urban data they used, the researchers found that the resulting global cooling ranged from 0.01 to 0.07 °C by 2300.
Although this temperature decrease is small relative to natural climate variability, the authors say that cities should promote the use of white or light-coloured surface materials because these can reduce air-conditioning usage and counteract the urban 'heat island' effect at minimal extra cost.
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Cooling effects of white roofs. Nature 485, 419 (2012). https://doi.org/10.1038/485419e