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Friday, February 19, 2010

Surabi Menon et al., Environ. Res. Lett., 5 (2010), Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets

Environmental Research Letters, 5 (2010) 014005 (11 pp.); doi: 10.1088/1748-9326/5/1/014005

Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets

Surabi Menon1, Hashem Akbari1,3, Sarith Mahanama2, Igor Sednev1 and Ronnen Levinson1

1Lawrence Berkeley National Laboratory, Berkeley, CA, USA
2Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, MD, USA
3Present address: Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, QC, Canada


The two main forcings that can counteract to some extent the positive forcings from greenhouse gases from pre-industrial times to present day are the aerosol and related aerosol-cloud forcings, and the radiative response to changes in surface albedo. Here, we quantify the change in radiative forcing and land surface temperature that may be obtained by increasing the albedos of roofs and pavements in urban areas in temperate and tropical regions of the globe by 0.1. Using the catchment land surface model (the land model coupled to the GEOS-5 Atmospheric General Circulation Model), we quantify the change in the total outgoing (outgoing shortwave+longwave) radiation and land surface temperature to a 0.1 increase in urban albedos for all global land areas. The global average increase in the total outgoing radiation was 0.5 W m−2, and temperature decreased by ~0.008 K for an average 0.003 increase in surface albedo. These averages represent all global land areas where data were available from the land surface model used and are for the boreal summer (June–July–August). For the continental US the total outgoing radiation increased by 2.3 W m−2, and land surface temperature decreased by ~0.03 K for an average 0.01 increase in surface albedo. Based on these forcings, the expected emitted CO2 offset for a plausible 0.25 and 0.15 increase in albedos of roofs and pavements, respectively, for all global urban areas, was found to be ~57 Gt CO2. A more meaningful evaluation of the impacts of urban albedo increases on global climate and the expected COoffsets would require simulations which better characterize urban surfaces and represent the full annual cycle.

Received 14 July 2009, accepted for publication 5 January 2010, published 21 January 2010.

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