Cooling Cities by Painting Roofs and Roads White

The Guardian (UK)
wrote about a plan by a scientist, Hashem Akbari, at the Lawrence Berkeley National Laboratory in California, to re-paint all urban roads and rooftops with white paint, which would cause significantly more sunlight to be reflected back into space, and help buy time to cut carbon emissions and address climate change. Akbari hopes a dozen large cities will re-paint their roads and rooftops with reflective, lighter paint.

The Guardian contends that “study after study has shown that buildings with white roofs stay cooler during the summer. The change reduces the way heat accumulates in built-up areas – known as the urban heat island effect (UHIE)- and allows people who live and work inside to switch off power-hungry air conditioning units.”  Reflective paint colors, such as white, or even light grey can help cool urban temperatures. “Computer simulations of Los Angeles show that resurfacing about two-thirds of roads and rooftops with reflective surfaces, as well as planting more trees, could cool the city by 2-3C.” Cooler cities also means less energy use for air conditioning. “On hot days in North America, up to 40% of all electricity can be consumed by air-conditioners, and each degree a city such as LA warms is reckoned to see the air-con turned up enough to need another 500MW – the output of a decent sized nuclear power station. Akbari estimates that widespread use of cooler rooftops could slash $1bn from electricity bills in the US alone.”

A few states and cities in the U.S. have already bought into the plan. In 2005, California has mandated that warehouses and other commercial premises with flat roofs re-paint them white.  U.S. cities, such as Houston, Chicago, and Salt Lake City, are considering his plan.

At the global level, roads and roofs cover more than half of surfaces in urban areas. Urban areas spread over 2.4% of the Earth’s land. If a majority of roofs in urban areas were re-painted a lighter, reflective shade, the amount of sunlight bounced off our planet would increase by 0.03%, enough to cool the Earth and cancel the warming caused by 44bn tonnes of CO2 pollution. However, critics note that the plan won’t stop many of the adverse effects of climate change. Kevin Anderson of the Tyndall Centre for Climate Change Research at Manchester University, said to The Guardian: “It won’t tackle global warming because carbon emissions are still rising,” he says. Like all geo-engineering schemes, it will need to be kept up indefinitely, he says, and does not address the growing acidification of the oceans, caused as extra CO2 dissolves. The cooling effect and energy savings in cities would be welcome though.”

Read the article

4 thoughts on “Cooling Cities by Painting Roofs and Roads White

  1. Lynn Stevens 03/20/2009 / 11:03 am

    Rooftops, yes. Roads, I’m not so sure.

    I think it could be a safety issue. White roads that reflect the sun will create additional glare for drivers. Think of the albedo rate of snow or water.

    I think it could also be a cost issue. How long will white roads stay white? How often would you have to paint them.

  2. , 03/21/2009 / 8:57 pm

    roofing, yep. this makes sense just for the owner. yet a charcoal black comp shingle seems to be a recent ‘trendy’ color.

    also, lighter surface exteriors suffer less sun-induced shrink/expansion damage. and interiors (walls, cabinets, etc) need lower lighting lumens.

    white roads would “show dirt” (eek!) 🙂
    perhaps asphalt can be tinted paler, to lightness level of concrete roads?

  3. Brute 10/17/2009 / 7:18 am

    Ah, just one small comment. About my solar panels… they’re black. And on my roof. And were very expensive to buy and install. I don’t think I’ll be painting them white any time soon…

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