White Roofs to Cool the World—Update and Recommendations

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) 527 -1060 Art. Rosenfeld@gmail. com 1

Global Cooling: Increasing World-wide Urban Albedos to Offset CO 2 July 28, 2008 Hashem Akbari and Surabi Menon Lawrence Berkeley National Laboratory H_Akbari@lbl. gov Tel: (510) 486 -4287 • • • 2 Arthur Rosenfeld California Energy Commission Arosenfe@energy. state. ca. us Tel: (510) 527 -1060 Published in Climatic Change (2009) A first step in geo-engineering which saves money and has known positive environmental impacts Albedo = reflectivity to sunlight

White is ‘cool’ in Bermuda 3

and in Santorini, Greece 4

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

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

Congratulations to UC Davis 8

White roofs are popular in Tucson, AZ 9

Punta Gorda, FL 10

Washington, DC (Federal) has problems 11

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

Temperature Rise (°C) 13 20 10 0 0. 0 40 30 0. 2 IR-Refl. Black 0. 4 0. 6 0. 8 Solar Absorptance Black Paint Green Asphalt Shingle White Asphalt Shingle Red Clay Tile Lt. Green Paint Lt. Red Paint 50 Al Roof Coat. White Cement Coat. White Paint Optical White Reflective roofs have lower temperatures in sunlight Galvanized Steel 1. 0

Solar reflective surfaces also cool the globe Source: IPCC 14

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

Global Cooling: Increasing World-wide Urban Albedos to Offset CO 2 July 28, 2008 Hashem Akbari and Surabi Menon Lawrence Berkeley National Laboratory H_Akbari@lbl. gov Tel: (510) 486 -4287 • • • 16 Arthur Rosenfeld California Energy Commission Arosenfe@energy. state. ca. us Tel: (510) 527 -1060 Published in Climatic Change (2009) A first step in geo-engineering which saves money and has known positive environmental impacts Albedo = reflectivity to sunlight

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 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). 17

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 18

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 about 600 million passenger cars world wide, and they each emit ~4 t CO 2/year. 19

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 20

Changes proposed for Title 24 -2011 • 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. 21

Dr. Anthony Eggert, Commissioner California Energy Commission (916) 654 -4930 Aeggert@Energy. State. CA. US 22