Friday, January 16, 2009

Paint It

Kevin Anderson of the Tyndall Centre for Climate Change Research at Manchester University says while the idea may involve simple science, the reason why it won’t work involves simple science also.

"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 adds, “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.”

Akbari responds by pointing out that his plan is not intended to replace efforts to cut carbon emissions; but, to work in conjunction with them.

"We can give the atmosphere time to breathe," he says. "I just don't see a downside to this idea. It benefits everybody and you don't have to have hard negotiations to make it happen."

In technical terms, the percentage of light reflected by a surface is called its albedo. A perfectly reflective surface has an albedo of 1. So, in terms of reflectability 1 is the gold standard. That doesn’t sound too bad or does it?

Let’s look at the albedo of our most common surfaces. Dark roofs reflect about 10-20% of sunlight; white surfaces tend to reflect approximately 50%; coloured paints have an albedo of 0.1–0.3; but, white paint has an albedo of 0.5-0.9; asphalt roads with their albedos as low as 0.05 can absorb up to 95% of the sun’s energy; the albedo of concrete can be up to 0.3; and tar and gravel just 0.1.

Akbari is not expecting everyone in the world to just suddenly rush out with paintbrushes and other reflective materials and change the landscape overnight. His mission is to get individuals, local authorities, builders and communities to think about albedo alongside cost, colour and design when it comes to repairs, maintenance and new construction.

"This is not just a question of painting things white. Roofs and roads are routinely repaired and replaced and, when it comes to a householder changing their roof, we want them to look at reflective options. That's the time to target people." He says an "aggressive" program could convert all cities within 10-20 years.

While convincing flat roof owners to paint them white should not prove much of a problem since flat roofs are only seen by overhead traffic. However, sloping roofs are visible from the street. Not only does painting or converting all these roofs to white take away some individuality, streets of white-roofed houses could dazzle on a sunny day as could road surfaces that are too light in colour. Too light a colour coupled with too much light becomes glare reflected into the eyes of motorists.

“No problem,” Akbari says, “reflective materials need not be white. Lighter colours such as grey are good too. And there are other ways to increase the albedo of materials. Pigments that bounce back infrared light can raise the reflectivity of dark surfaces by 40% without any obvious change in colour. They are not as effective as white, which bounces back visible wavelengths of light too; but, they are much better than conventional materials.”

The Japanese are usually among the first when it comes to pioneering new technologies; and, once again they are in the forefront on this issue. The Public Works Research Institute in Japan has been experimenting with paints with pigments that bounce back infrared light applied to conventional asphalt surfaces. They seem to have conquered both problems.

Their prototype road reflects 86% of infrared light (keeps surface cool); yet, reflects 23% of visible light (keeps glare down). Wondering how these changes would affect pedestrians, researchers recruited volunteers in the summertime to “stand on the paint-coated pavement and conventional pavement.” The volunteers actually preferred the coated road because it kept their feet cool.

There are other benefits too. Computer simulations of Los Angeles show that by resurfacing about two-thirds of roads and rooftops with reflective surfaces, in addition to planting more trees, it is possible to cool the city by 2-3C. A reduction of 2-3C would be blessing enough; but, in addition this would reduce LA smog as much as a total ban on cars and trucks. I was in LA about 20 years ago; (I can only imagine what it is like now) and, I could see the smog miles before I could see the city. I have never been back – have no urge to go back. There’s just something about being able to actually see the air I’m breathing that I find a bit off-putting.

Home owners would reap the benefit of having a cooler roof by saving a fortune in electricity bills. On hot days in North America, up to 40% of all electricity can be consumed by air-conditioners. Air-conditioners suck energy like almost no other appliance. For each degree a city such as LA warms (pop. Approx. 3.8 m), it is estimated the air-conditioners are turned up enough to need another 500 MW. To put things in perspective, this is 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. Can we even wrap our minds around the concept of the electricity saved worldwide? That alone, will set other good things in motion.

But why should we bother with places that are more renowned for their bad weather than their days of weak sunshine and extra vitamin C? Akbari says his estimates of the global cooling potential of reflective cities are based on a global average, so, the cloudier places will be made up for by the sunnier spots. "It's absolutely worth doing in the UK," he says. “And,” he adds, “he might just have found a way to pay for it.”

His plan is brilliant. It should be presented to governments everywhere. Akbari’s plan and reasoning is this:

“Each 10 sq m of urban surface changed from dark to white has the same cooling effect as preventing the release of a ton of carbon dioxide. So why not include such resurfacing in carbon offset schemes? Just as money from green consumers and firms anxious about their carbon footprint is used to fund projects that plant trees, fit green light bulbs and develop renewable energy, in exchange for carbon credits; so, it could pay people across the world to paint, coat and resurface.”

At today's carbon prices, changing the colour of an average roof could net the householder £150 ($224 US); and, Akbari's global scheme could together generate more than £500m ($746.4 m US). "We want to target 30 to 40 cities initially; but, within a few years we hope it will mushroom around the world," he says.

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