1 White Roofs to Cool the World---- Update and Recommendations Rosenfeld Symposium UC Davis EE Center March 9, 2010 Arthur H. Rosenfeld, Former Commissioner California Energy Commission Home-Office Phone: (510)

2 Global Cooling: Increasing World-wide Urban Albedos to Offset CO 2 July 28, 2008 Hashem Akbari and Surabi Menon Lawrence Berkeley National Laboratory Tel: (510) Arthur Rosenfeld California Energy Commission Tel: (510) Published in Climatic Change (2009) A first step in geo-engineering which saves money and has known positive environmental impacts Albedo = reflectivity to sunlight

3 White is ‘cool’ in Bermuda

4 and in Santorini, Greece

5 and in Hyderabad, India …and widely in the State of Gujarat, India

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7 Cool Roof Programs around the World U.S. Europe Asia Middle East China India (Hyderabad demos; see graph at right. White roof saved 15%).

8 Congratulations to UC Davis

9 White roofs are popular in Tucson, AZ

10 Punta Gorda, FL

11 Washington, DC (Federal) has problems

12 Cool roof technologies flat, white pitched, white pitched, cool & colored Old New

13 Reflective roofs have lower temperatures in sunlight Temperature Rise (°C) Galvanized Steel IR-Refl. Black Black Paint Green Asphalt Shingle Red Clay Tile Lt. Red Paint Lt. Green Paint White Asphalt Shingle Al Roof Coat. Optical White White Paint White Cement Coat. Solar Absorptance

14 Solar reflective surfaces also cool the globe Source: IPCC

15 A small house, 1000 ft 2, of white roof, replacing a colored roof, offsets the emission of 10 tonnes of CO 2

16 Global Cooling: Increasing World-wide Urban Albedos to Offset CO 2 July 28, 2008 Hashem Akbari and Surabi Menon Lawrence Berkeley National Laboratory Tel: (510) Arthur Rosenfeld California Energy Commission Tel: (510) Published in Climatic Change (2009) A first step in geo-engineering which saves money and has known positive environmental impacts Albedo = reflectivity to sunlight

17 Akbari et al. now confirmed by general circulation model runs Akbari et al. (2009) was a calculation based on current knowledge and some crude estimates that the cloud cover over all cities averaged 50% all year. This corresponds to 10 tonnes of CO 2 offset per 1000 square feet of white roof (vs. dark roof). Menon et al. (Jan 2010) in Environmental Research Letters ran a Global Land Surface Model (part of GCM). They corroborate Akbari et al. In fact they get 30% larger cooling, e.g. 13 tonnes of CO 2 offset per 1000 square feet of white roof (vs. dark roof).

18 And Oleson et al. agree with Menon et al. Oleson et al. (2010) have run NCAR’s GCM and urban climate models. They also corroborate Menon et al. and also get ~13 tons of CO₂ offset by 1000 sqft of white roof. Sources: –Oleson et al., National Center for Atmospheric Research, Boulder, CO, Geophysical Research, in press –private communication with Keith Oleson

19 How much CO 2 is offset if we whiten all eligible urban flat roofs world-wide? Answer: 15 gigatonnes (Gt) –half a year’s worldwide emission –gigatonne = billion metric tons If implemented over 15 years (the life of a roof or a program) this is ~1 Gt/year. 1 Gt/year is equivalent to offsetting the emissions of 250 million cars for 15 years. –There are about 600 million passenger cars world wide, and they each emit ~4 t CO 2 /year.

20 California “Title 24” building energy efficiency standards Title 24, 2005, effective 2007 –Commercial Buildings –If roof is “flat” and building has a/c, then white is “prescribed.” Title 24, 2008, effective 2010 –Residential: if roof is flat, white is prescribed statewide –If sloped, in 5/16 hottest climate zones, white or cool colored roofs are prescribed. Georgia and Florida credit white roofs ASHRAE credits white and cool roofs. IEEC, next cycle, will probably credit cool colors & white roofs

21 Changes proposed for Title When calculating economic optimum design, internalize the complete CO 2 externality, so include non-air conditioned buildings. Apply this externality also to pavements, automobile roofs; indeed roofs of all passenger vehicles including trains. Photo of twin towers in Hyderabad where white roof saved 15% of a/c load of top floor.

22 Dr. Anthony Eggert, Commissioner California Energy Commission (916)