If you’ve ever crossed a hot car park in summer, you know about albedo. Dark colours absorb heat, while lighter colours reflect it. That’s one of the principles behind the idea that a melting arctic may be a self-reinforcing feedback loop: relective ice melts and is replaced by dark water, which holds heat better and melts the remain ice even faster.
We can also use this principle to our advantage however, by increasing albedo in places where we have a little more control of the environment than we do in the Arctic – cities. Cities are prone to the urban heat island effect, being warmer than surrounding areas by 1-3C. They lack the green spaces that serve to cool the air, are full of activity and machinery, and they’re covered in acres of dark and baking tarmac.
It’s those man-made surfaces that offer us an opportunity to increase reflectivity. Using whiter concrete could reduce the heat absorption of roads and car parks, lowering the temperature in the immediate vicinity. Roofs constitute about 20-25% of urban areas, and pavements about 40%, so it’s a lot of space to work with and it could be a useful adaptation tool as cities warm. Painting the roofs of buildings white offers a double reward. It lowers external temperatures, but it also cools the building by up to 30% and reduces carbon emissions from air conditioning.
There are a number of projects at work painting roofs white. NYC cool roofs encourages New Yorkers to paint their roofs as part of the city’s plan to reduce its carbon emissions by 30% by 2030. According to their estimate, every 1,000 square feet of roof painted cuts one tonne of CO2.