摘要：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
CO2 offsets would require simulations which better characterize urban surfaces and represent the
full annual cycle.
