Green cities have higher evapotranspiration and superior ground shading, which significantly reduces energy usage in cooling. Green space is also potentially more conducive to walking and cycling, so the carbon and albedo benefits of white cities have to be set against these factors.
A On Apr 13, 2012 2:10 PM, "Hashem Akbari" <[email protected]> wrote: > The offset is only for emission of all the cars (not the entire emission). > > I agree the delay in global warming is about 2-3 years. > > Greener cities do not have a higher solar reflectance. > > Best, > Hashem > > On 13/04/2012 9:00 AM, Ken Caldeira wrote: > > *sorry .. I just woke up (6 AM here) and am pre-coffee. Didn't seen it > was cars only.* > > On Fri, Apr 13, 2012 at 5:57 AM, Ken Caldeira < > [email protected]> wrote: > >> *The scientists estimated that urban areas make up roughly 1% of the >> total land area in these regions; increasing albedo by 0.1 only in urban >> areas would be equivalent to a global change in land-surface albedo of >> 0.001.* >> *"Increasing albedo of urban areas by about 0.1 – increasing flat roof >> albedo by 0.4, increasing sloped roof albedo by 0.25, and pavement albedo >> by 0.15 – cools the globe equivalent to offsetting over 100 Gigatonnes of >> carbon dioxide emissions," said Akbari. "This is equivalent to offsetting >> the emissions for all the cars in the world for the next 20–30 years."* >> >> A global change in land surface albedo of 0.001 is a change in global >> surface albedo of 0.0003. >> >> If half the land is under clouds this might lead to a global >> top-of-atmosphere albedo change of something like 0.00018. >> >> A doubling of CO2 can be compensated by a global albedo change of >> 0.018, which suggests that an urban albedo change 0.01 would have a result >> that is about 100 times smaller. >> >> If a doubling of CO2 occurs in a century, this suggests this approach >> could delay warming by 1 year, not 20 to 30 years as claimed in this news >> report. >> >> Perhaps Damon or Hashem can shed some light on this apparent >> discrepancy. >> >> Another question is the relative benefits of greening cities versus >> whitening cities. >> >> >> _______________ >> Ken Caldeira >> >> Carnegie Institution Dept of Global Ecology >> 260 Panama Street, Stanford, CA 94305 USA >> +1 650 704 7212 [email protected] >> http://dge.stanford.edu/labs/caldeiralab @kencaldeira >> >> *Currently visiting * Institute for Advanced Sustainability Studies >> (IASS) <http://www.iass-potsdam.de/> >> *and *Potsdam Institute for Climate Impact Resarch >> (PIK)<http://www.pik-potsdam.de/> >> *in Potsdam, Germany.* >> >> >> >> On Fri, Apr 13, 2012 at 5:37 AM, Andrew Lockley <[email protected] >> > wrote: >> >>> Increasing albedo - why we should paint the roof white to reduce energy >>> use in summer http://environmentalresearchweb.org/cws/article/news/49268 >>> >>> Replacing roofs and pavements with more reflective versions when they >>> wear out could cut global temperatures by up to 0.07 °C, equivalent to a >>> reduction in carbon-dioxide emissions of around 150 billion tonnes. That's >>> according to researchers in Canada who used a global climate model to look >>> at the effects of albedo changes in urban areas. >>> >>> "Scientists have been proposing novel ideas – mostly untested –for >>> geoengineering of global climate," Hashem Akbari of Concordia University >>> told environmentalresearchweb. "Humans have had experience with white >>> buildings and reflective pavements for thousands of years without any >>> unknown negative side-effects. Hence cool urban surfaces should be our >>> geoengineering 101." >>> >>> Akbari and colleagues from Concordia used the University of Victoria >>> Earth System Climate Model (UVic ESCM) to investigate the effect of albedo >>> increases of 0.1 until 2300 over all land between latitudes of + and –20° >>> (i.e. roughly from Mexico City and Hanoi in the north to Bulawayo, Zimbabwe >>> in the south), and between + and –45° (approximately from Lyon, France and >>> Portland, US to Dunedin in New Zealand). The team used both a >>> business-as-usual emissions scenario and an aggressive mitigation scenario. >>> >>> The albedo increase on all land between + and –20 ° latitude would >>> decrease temperature by roughly one degree over 20 years, while the 45° >>> latitude case would double this decrease. After 200 years, the decreases >>> would be 1.3 K and 3 K. >>> >>> The scientists estimated that urban areas make up roughly 1% of the >>> total land area in these regions; increasing albedo by 0.1 only in urban >>> areas would be equivalent to a global change in land-surface albedo of >>> 0.001. >>> >>> "Increasing albedo of urban areas by about 0.1 – increasing flat roof >>> albedo by 0.4, increasing sloped roof albedo by 0.25, and pavement albedo >>> by 0.15 – cools the globe equivalent to offsetting over 100 Gigatonnes of >>> carbon dioxide emissions," said Akbari. "This is equivalent to offsetting >>> the emissions for all the cars in the world for the next 20–30 years." >>> >>> To firm up their calculations, the researchers employed two estimates of >>> urban area – from the Global Rural and Urban Mapping Project (GRUMP) and an >>> analysis based on MODIS satellite data. The GRUMP results suggest that >>> global urban areas are more than five times larger than the MODIS data set >>> indicates. >>> >>> The climate model revealed that increasing albedo by 0.1 only in >>> GRUMP-designated urban areas would produce long-term cooling of 0.07 K, >>> equivalent to 130–150 Gigatonnes of carbon. Using the MODIS data for urban >>> areas, in contrast, would cool the Earth by 0.01 K, equivalent to 25–30 >>> Gigatonnes of carbon. >>> >>> According to Akbari, albedo increases could lead to air-conditioning >>> savings of about 20% for space under the roof. "This is about $50 bn >>> savings per year and carbon dioxide savings of about 0.4 Gigatonnes per >>> year; over the next 100 years that is an emission reduction of 40 >>> Gigatonnes," he said. "The direct cooling of the Earth by reflecting >>> radiation back to space is an added bonus that actually counters global >>> warming while putting dollars in our pocket." >>> >>> The researchers found that the effect of albedo change did not depend to >>> a large extent on the carbon-dioxide emissions scenario. That said, >>> aggressive mitigation appeared to produce a roughly 10% larger temperature >>> decrease, which the team ascribed to stronger snow-albedo feedback. >>> >>> "We should develop policies for no-regret no-cost global cooling >>> measures," said Akbari. "Cool cities will save all the people in the world >>> equally and the value of the dollar saved is significantly higher in >>> developing countries than the developed country (e.g. $1 saved in the US >>> pays for 10 minutes of a labourer in the US; in the developing countries >>> that pays for a day of labourer)." >>> -- >>> 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. >>> >> >> > > -- > Hashem Akbari > Department of Building, Civil and Environmental Engineering > Concordia University > 1455 de Maisonneuve Blvd. West EV006.409 > Montreal, Quebec, Canada H3G 1M8 > Tel: 514-848-2424 X3201 > Fax: 514-848-7965 > Email: [email protected] > ----------------------------------------------- > Hashem Akbari > Departement de genie du batiment, civil et de l’environnement > Universite Concordia > 1455 boul. de Maisonneuve ouest EV006.409 > Montreal (Quebec) Canada H3G 1M8 > Tel: 514-848-2424,poste 3201 > Telec: 514-848-7965 > Coumel: [email protected] > ========================================== > > -- 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.
