Plants on Roof Tops
Name: Claudia L.
Date: July 2004
Can you please tell me if their would be a benefit to the environment
by planting trees on skyscrapers or using reflective surfaces as roof
tops on those same buildings?
Yes, there would be a benefit if either of your suggestions were adopted.
Planting trees would shield the building from the direct rays of the sun
(especially if the building is not very tall). Further, due to the water
emitted by the trees which is evaporated, especially on warm days, the top
of the building would be further cooled. One could, of course, put water
tanks on the roof; the evaporation of the water would cool the building
without the trees being needed.
Reflective surfaces could work well also. The sunlight could be returned to
space without heating the building or, in fact, any part of the earth.
Further, if the light is reflected specularly -- without change of
wavelength -- there would not be a greenhouse effect. The greenhouse effect
works if sunlight is incident on the earth and warms the earth, which then
radiates the heat energy at a longer wavelength (characteristic of the
temperature of the earth and not of the sun). The longer wavelength
electromagnetic radiation is efficiently trapped by the atmosphere,
especially if it contains significant amounts of carbon dioxide and other
Best, Dick Plano, Professor of Physics emeritus, Rutgers University...
I do not see any harm provided the roof is strong enough to support the
plants and their soil. Dirt is pretty heavy.
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Update: June 2012