Painting roofs white and creating lighter coloured pavements and roads are recognised as ways to reflect heat in urban areas and help combat global heating. However, a new study shows that this geoengineering technique unexpectedly causes temperatures to rise in the surrounding region.
Scientists have previously used large-scale climate models to assess the climate impacts of increasing albedo (reflectivity) on land, but these do not pick up changes in small-scale atmospheric circulation. Yu Cheng and Kaighin McColl from Harvard University simulated the localised changes and found that increasing albedo resulted in increased convection at the boundary of the high-albedo area – similar to the breezes found where sea meets land.
Their results, published in Geophysical Research Letters, show that the increased convection altered cloud cover, resulting in less rain and higher temperatures in the surrounding region, negating the cooling achieved in the high-albedo area.
The researchers point out that this could exacerbate climate inequity if wealthy neighbourhoods adopt this geoengineering technique and push additional warming into surrounding poorer neighbourhoods. For example, if a region the size of Trafford, Greater Manchester, installed white roads and roofs then the 1km strip around this region – home to approximately 300,000 people in an urban area – would experience excess heating.
