Painting world's roofs white would save $1 trillion in energy costs
Black is the most effective colour for trapping the sun's heat, while white is the best at repelling it. Black pavement accounts for 40% of urban surfaces while roofs -- typically covered with black or dark shingles --account for 20% to 25%.
As a result, city dwellers live in an "urban heat island" where summer temperatures are up to 6.7 degrees higher than in the surrounding countryside. That's because, as Joni Mitchell said, we've "paved paradise and put up a parkin' lot."
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Commentaires
LEED standard is a little flawed on this issue
I design, and sell buildings for a living. I have been very encouraged by the increasing emphasis in the marketplace on LEED buildings, energy and resource efficiency, and controlling operating costs in recent months. It has always irked me though that LEED offers a point for installing a roof system which is highly reflective, and reduces emmisivity, irrespective of location. I recently designed a LEED project for Fort McMurray. In this instance, the urban heat island effect is minimal, while the Heating costs are really high. There was still a LEED point for installing an expensive roof that will demonstrably increase the energy consumption of the building, while having a negligible impact, on a negligible problem. I guess that this is an example of the difficulty of mandating one size fits all solutions, rather than implementing broader based energy taxes and incentives. The good news is that there is a huge demand for cleaner, leaner construction, and there will be a significant impact on new construction efficiency over the next year or two. We can thank local municipal initiatives for the majority of these savings that we will all enjoy the shared benefits from.
Changing colors..
I'm pretty sure the technology exists so that shingles would get get lighter in color as they get hotter, and darker as they get colder.
If this can't be done passively, it certainly can be done actively (ie, using electricity or mechanically). The energy savings probably make sense in some climates.
The dumbest way you can achieve this is to put a bunch of rollers on a roof, and the rollers could just rotate around picking a warm or cold side as the case may be.
Has anyone thought of asking a local university to work on this kind of project?