Urban Heat Islands, White Roofs and Climate Change

Image via Wikipedia

Effects of Urban Surfaces and White Roofs on Global and Regional Climate (Abstract, Mark Z. Jacobson, John E. Ten Hoeve, Journal of Climate, Sep. 12, 2011)

From the meteorological modelling community comes an article today examines the significance of urban heat islands as a factor in climate change- turns out that it is not. It also tests the hypothesis that painting roofs white would reduce the amount of warming of the atmosphere and thereby delay climate change. The model shows that the converse is true because there would be less heating at the surface resulting in less convection and less cloud which globally would allow more sunlight to warm the atmosphere.

Key Quotes:

“The urban heat island effect is caused mostly by replacing soil and vegetation with paved roads, sidewalks and buildings. Paving prevents evaporation of water from the soil and plant leaves. Since evaporation is a cooling process, reducing evaporation warms cities”

"Between 2 and 4 percent of the gross global warming since the Industrial Revolution may be due to urban heat islands.. compare this with the greenhouse gas contribution to gross warming of about 79 percent and the black carbon contribution of about 18 percent."

“if all the roofs in urban areas were painted white, it would increase, not decrease, global warming…A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ~0.02 K but to warm the Earth overall by ~0.07 K…largely because they reduced cloudiness slightly by increasing the stability of the air, thereby reducing the vertical transport of moisture and energy to clouds”

"Cooling your house with white roofs at the expense of warming the planet is not a very desirable trade-off,"

Related articles

• White roofs are not a silver bullet for cooling planet, study finds (guardian.co.uk)
• Urban 'heat-islands' only a small factor in global warming (summitcountyvoice.com)
• White Roof Project Helps NYC Beat The Heat (shareable.net)
• Painting Your Roof White Doesn't Work (fastcompany.com)
• The Moscow Warming Hole (realclimate.org)
• Cool roofs really can be cool (physorg.com)