When we consider the many actions we may take to fight global warming and become more responsible citizens of earth, do we often think of our roofs?  At most, green roofs are the topic of impassioned discussion, but other alterations aren’t mentioned or considered.

The discussion of altering roofs first became a heated (ha) topic in the U.S. when the U.S. Secretary of Energy, Steven Chu, a Nobel prize-winning scientist, brought the concept of white roofs to the table in 2009. He proposed that, though it may seem a silly action to suggest, if we could make all of the roofs and dark paved surfaces white, we would be able to save emissions equal to taking all the cars off of the roads for eleven years.

Using white surfaces to fight warming works because the white roofs reflect the Sun’s rays before they are absorbed; after absorption the rays are only emitted by the receiving material (e.g. a black roof, black pavement, etc.) as heat (long-wave radiation or infrared), which has a hard time getting back out through the atmosphere. The shortwave (UV) rays that the sun sends in are much more capable of penetrating the atmosphere, in both directions. As a result, the white roofs effectively send the heat back out the way it came, before it’s turned into heat!

Keith Oleson, a National Center for Atmospheric Research scientist, performed a study released in January of this year that found that white surfaces could reduce the urban heat island as much as 33% in some cities.

This concept continues to be relevant; a study came out last month that suggests that urban areas are warming at accelerated rates when compared to rural areas. The study also found that areas that have the highest potential for increased urban heat island effects, have the most potential for increased populations within the next 50 years, meaning more people in smaller spaces, including many without access to air conditioning. While daytime temperatures may warm equally, the nights in urban areas are expected to grow much warmer, resulting in a smaller difference between day and night temperatures as global warming accelerates; city residents will say goodbye to the relief of a cool night after a sweltering sunny day. Since this is expected to be a significant and near-future impact, several actions were suggested within the study, including usage of green spaces, strategic architecture, and white roofs.

Additionally, the aspect of home heating comes into play. Dr. Chu insisted that the white roofs not only reflect sunlight to keep homes cool in the summer, but that they would actually reflect heat back into homes in the winter, effectively reducing costs (and emissions) in both seasons. This was disputed by Keith Oleson, who suggests that in winter, the effects of white roofs would be the same, cooling by reflection. This conclusion illustrates the point that the world is not uniform; white roofs may be a perfect tactic for urban areas in locations that do not experience cold, but perhaps a less ideal choice for locations with less-than-mild winter months.

Here’s a video of Secretary Chu’s explanation that is posted on the US Department of Energy’s official YouTube page (also a great source for high quality video of the oil leaking into the Gulf of Mexico, presently…).