Hashem Akbari, head of the Heat Island Group at LBNL interviewed by NPR's Ira Flato on Science Friday. Much of this discussion has been presented here before, but some new information.
Akbari is also a professor at Concordia U. in Montreal, where he is advising the province of Quebec on how to adopt Calif. cool roofs and roads energy policies. Akbari says the goal is not to paint or cover existing roofs or roads with a white surface material, because the incremental cost wouldn't be worth it, but instead, to make this change when the surfaces would normally be replaced, about 20 years for a house. For each 100 SF of roof area, a conversion from black to white (most roofs in the U.S. on residential buildings are gray or even black), 1 ton of CO2 emissions would be offset and for an average roof area of 2000 SF, 20 tons of CO2. Note that as I've mentioned before, that calculation only holds as long as the roof is white and is in place, since the CO2 lifetime in the atmosphere is variable and only half of what is emitted today will be gone after 30 years. Thus, it's important that regulators, builders and the public not overcount the benefits of doing this. Akbari says that lightening (need to be clear exactly how light--realize this was a 12-min interview, but there are fine points to this) of all roofs in the tropics and temperate regions would offset 24GtCO2, almost the same as today's human emissions of 25GtCO2. Again, need to be clear that this is a one time offset. It wouldn't offset 24GtCO2 in 2009 and then another 24Gt in 2010. It's the same 24Gt over and over again. He also used the example of how this compares with vehicle emissions, stating that of the 600 million passenger vehicles in the world, each emitting 4 tons of CO2 per year, the cool/white roofs program if implemented maximally would offset the CO2 emissions from 300 million cars for 20 years, again the same 24Gt CO2. Flato then asked about the impact of solar panels on roofs vs. making the roofs lighter in color. Akbari said that since only 20-30% of the roof is typically covered in solar panels, both could be used. The discussion then turned to asphalt and other paved surfaces like driveways and sidewalks. Akbari said one alternative is to use "grasscrete" a mixture of concrete and grass where the grass grows in the spaces in this cinderblock-like material. Water is a problem, so it shouldn't be used where ponding occurs. Lighter colored aggregates for road paving could also be used, especially low traffic roads where the aggregate can be sprayed on the surface. Concrete roads, driveways and sidewalks are more reflective than black asphalt. The reflectivity of aged concrete is about 0.15 vs that of black asphalt and is around 15 degrees F cooler. I've made this same measurement myself. The goal, says Akbari is to get the 100 largest cities in the world, the so-called megacities, to adopt these policies. Energy Sec'y Chu made this a goal some time ago. So far, cities showing an interest include NYC, Taipei, Sao Paulo, Osaka, Hyderabad and Delhi. http://www.npr.org/templates/story/story.php?storyId=106733879&ft=1&f=1007&sc=YahooNews Paint The Town White Listen Now [11 min 57 sec] add to playlist | download Talk of the Nation, July 17, 2009 · Light-colored clothing is cooler in the sun, and the same goes for cities. Hashem Akbari has studied the advantages — in reduced energy use and lower carbon dioxide emissions — of switching dark-colored roofing and pavement materials for lighter, more reflective alternatives. Comments C valhad (NPRCapeCod) wrote: This was an interesting discussion, but how about delving a little deeper. Given the potential for lighter & reflective surfaces to offset carbon emmissions and reduced heat island affect- What is the consequence of a proliferation of rooftop solar panels and commercial solar energy installations? The panels are dark to absorb heat and energy...yet smooth and reflective. Is there an un-discussed global climate change penalty to solar thermal and/or electricity? Saturday, July 18, 2009 4:57:58 PM --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
