Tuesday, November 29, 2005

I'm doing my bit...

Would it be possible to reduce the impact of the greenhouse effect by painting roofs of buildings white to reflect sunlight in the same way the polar icecaps do? Does a paint exist that would mimic the reflective properties of snow?

Painting roofs white would reflect more sunlight and it might also compensate for global warming. The Global Rural Urban Mapping Project (GRUMP), undertaken by the Earth Institute at Columbia University in New York, shows that roughly 3 per cent of the Earth's land surface is covered with buildings.

The Earth has an albedo of 0.29, meaning that it reflects 29 per cent of the sunlight that falls upon it. With an albedo of 0.1, towns absorb more sunlight than the global average. Painting all roofs white could nudge the Earth's albedo from 0.29 towards 0.30. According to a very simple "zero-dimensional" model of the Earth, this would lead to a drop in global temperature of up to 1 °C, almost exactly cancelling out the global warming that has taken place since the start of the industrial revolution. A zero-dimensional model, however, excludes the atmosphere and, crucially, the role of clouds. It would be interesting to see if more sophisticated models predict a similar magnitude of cooling.

Hey, all that looking into the thermal efficiency of types and colours of roofing may be a good thing, not just for me, but for the planet. I found a chart somewhere that compared the heat transmission of different roofing types, here is a quick summary:
  • Zincalume - 5% heat transmission
  • Colourbond (Off-white) - 10% heat transmission
  • Colourbond (Other colours) - 19%+ heat transmission
  • Clay/concrete tiles (Any colour) - 25%+ heat transmission


I'm doing my bit...

New Scientist Back Page - Snow laughing matter

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