Part 5 in the Series: ‘Solving the Problem with Roofs’

In the fight against global warming, one basic but highly effective method often gets ignored – painting rooftops white. This is known as a ‘Cool Roof’, and it reflects the suns rays back into the atmosphere rather than absorbing them.

Ordinary rooftops in New York City have been measured at temperatures over 80 degrees celcius, or 180 fahreneheit, which heats the building and increases the need for air conditioning. In buildings where cool roofing has been employed, the amount of energy used for cooling has dropped significantly, reducing bills by between 20 and 70 percent.

So why aren’t white rooftops a common sight? Perhaps we are resistant to this change because dark roofing is so prominent. With this in mind, MIT have created the Thermeleon Tile, which is normally black, but turns white when hit by sunlight.  It works by placing a common polymer between two plastic layers, with a black one at the back. When cold, the polymer is dissolved and the black back shows through, but when it heats up the solution forms light-scattering droplets which turn the tile white and reflect sunlight. These tiles can reduce cooling bills in the summer by 20%

Cool Roofing is so efficient, that if 80% of American homes converted to cool roofs, it would be the equivalent of taking 1.2 million cars off the road, annually. And if all rooftops in the tropical and temperate regions of the world were equipped with cool roofs, the energy savings would be the equivalent of taking all 600 million of the worlds cars off the road for 18 years.

The science behind Cool Roofs can apply to more than just roofing. Roads and paving are similarly unreflective, returning only a fifth of the sunlight that hits them. There are hundreds of millions of miles of hard surfaces in the world, with the majority being black. America has 2.5million miles of unreflective hard surfaces, which, if turned white, would reflect 5 trillion watts of sunlight back into the atmosphere ever year. To give that some perspective, NASA estimates that 2 trillion watts of continuous global heating will cause the Greenland ice sheet to melt. Essentially, the impact of turning roads and rooftops white is immense.

So… where’s the paint?

Image courtesy of Lornette’s Pics on flickr