Not Black and White: The Complications of White Roofs

Source: Jaun Carlos PE

After talking about green roofs, I was excited to laud the advantages of white roofs. They increase the albedo of the roofs allowing sunlight to bounce off of them. Which in turn keeps homes and cities cooler, so less energy is spent running the air conditioning. Unlike green roofs, they can be a cheap renovation for any building. (That's US$151 savings during installation for ever square meter!) Pack up shop, we solved the crisis with a few cans of paint!

I should have known that it might be too good to be true. A Stanford study looked at the global effects of a world filled with white roofs and found that the price for a locally cooled city was an increase in total global temperature. Their model predicted a .02^oC decrease in temperature around areas with white roofs but an increase of .07^oC worldwide. Part of the problem is soot and other air pollutants, heated from above and below, causing extra warming.

A study of the economic costs and benefits of environmental roofing found that white roof more economical for global cooling.  However, this was based on CO₂ offset by saving energy and relief of the urban heat island. Since there was no mention of the global heating caused by increased white roof, I tend to be a little skeptical.

Even if the white roof didn't warm the planet on a global scale, there are some areas where they would still not be worthwhile on the local scale. Cities with cooler climates may find that the savings from cooling in the summer are not offset by the additional heating in the winter. 

I wish I could say that a white roof is a great substitution if you can't have a green roof. However based on my reading, I'm afraid that running blindly into adapting white roofs may backfire. So for now, if it's not easy being green consider being solar. Perhaps absorbing light and using it as clean energy is better than reflection.