Hashem Akbari from LBNL discusses some of the benefits of increasing urban 
albedo.  He notes that roofs on average last around 20 years, but it's 
important to note that with the varied lifetime of CO2 in ambient air, any 
carbon credit scheme based on roof whitening will have to amortize the benefit 
over the percentage of the CO2 lifetime.  Example:  if half the CO2 emitted 
today is gone in 30 years, then only 20/30 of the radiative forcing from that 
half could be offset partially by whitening a particular roof that lasts 
exactly 20 years.  Similar lifetimes of surfaces vs. CO2 have to be established 
for pavement and other surfaces to be considered.  How homeowners or cities 
could receive credits and have the roof whiteness verified over such long 
periods of time requires further study.  The potential for fraud is great, 
especially in developing nations.


 Play 
Cooling the Earth, One Roof at a Time AP - Tue Apr 7, 7:33 PM ET 
Scientists are suggesting that homeowners replicate the reflective power of sea 
ice with roofs that reflect the sun's rays to help reduce carbon emissions. 
(April 7)

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