Radiative forcing and temperature response to changes in urban albedos and associated CO ₂ offsets

Abstract

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 CO 2 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 CO 2 . A more meaningful evaluation of the impacts of urban albedo increases on global climate and the expected CO 2 offsets would require simulations which better characterize urban surfaces and represent the full annual cycle.

Citywide Impacts of Cool Roof and Rooftop Solar Photovoltaic Deployment on Near-Surface Air Temperature and Cooling Energy Demand

“…Many studies reveal that the large-scale deployment of roofing technologies is an effective means of reducing energy consumption (e.g., Akbari et al 2009;Oleson et al 2010;Menon et al 2010;Salamanca et al 2012a;Cotana et al 2014;Georgescu et al 2014). Cool roofs, by virtue of increased reflectivities, absorb less incoming shortwave radiation than dark roofs, thereby promoting a lower skin temperature.…”

Evaluating the Role of Snow Cover in Urban Canopy Layer on the Urban Heat Island in Sapporo, Japan with a Regional Climate Model

“…As a result, a local climate, known as the urban heat island, forms in urban areas in which the local air temperature is higher than that of the surrounding rural area (e.g., Oke 1987;Gartland 2008;Synnefa et al 2008;McCarthy et al 2010;Menon et al 2010;Jacobson and Ten Hoeve 2012). Urban heat island intensity (UHI) or the urban-rural temperature difference depends on the scale of urban areas (population and energy consumption) and urban morphology (Oke 1987;Fujibe 2011).…”

“…It is also well known that the higher albedo of urban surfaces results in reduced surface air temperature (Synnefa et al 2008;McCarthy et al 2010;Menon et al 2010;Olsen et al 2010;Jacobson and Ten Hoeve 2012). However, few studies have quantitatively evaluated the effects of snow at an urban scale.…”

Soiling of building envelope surfaces and its effect on solar reflectance—Part I: Analysis of roofing product databases

“…Widespread use of reflective roofs can also cool outside air, helping mitigate the urban heat island effect [2] and potentially slowing global warming [3][4]. However, the solar reflectance (fraction of incident sunlight reflected) of an initially reflective building envelope surface is often reduced by soiling and weathering [5].…”