Increasing the reflectivity or albedo of roofs and pavements in urban areas could offset greenhouse gas emissions by a significant amount, according to an open access paper published last month in the IOP journal Environmental Research Letters. The research performed by scientists at Lawrence Berkeley National Laboratory and NASA’s Goddard Space Flight Center shows that a 25% and 15% increase in the albedos of roofs and pavements, respectively, in urban areas, could lead to an offset of approximately 57 billion tonnes of carbon dioxide.
Surfaces with high albedo reflect more solar radiation, preventing the radiation from heating the surface and the atmosphere. Introducing “cool roofs” and more reflective paving materials could replace some of the albedo that has been lost through the melting of Arctic sea ice.
Based on the radiative forcing obtained in this study, the potential emitted CO2 offset for a 0.25 and 0.15 increase in albedos of roofs and pavements in urban areas is about 57 Gt of CO2. If the annual cycle was considered in this work, the offset may be lower. Both studies indicate a qualitatively similar response of a reduction in radiative forcing or an increase in total outgoing radiation for an increase in urban albedo and the values indicate an approximate range in potential emitted CO2 offset that may be expected if urban albedos were increased.—Menon et al.
Increasing urban albedo is something that should be done now to buy time for implementing other near-term and long-term climate mitigation strategies. Although it does not solve the root of the climate change problem—substantial reductions in CO2 and other climate forcers are essential for that—urban albedo can delay the onset of more severe climate impacts, and reduce the risk of passing the thresholds for abrupt and irreversible climate changes.—Durwood Zaelke, President of the Institute for Governance & Sustainable Development (IGSD)
In addition to increasing urban albedo, other fast mitigation measures that will result in significant near-term reductions to avoid passing the tipping points for abrupt climate change include reducing emissions of black carbon soot, methane, and tropospheric ozone, as well as using the Montreal Protocol ozone treaty to phase down hydrofluorocarbons, which could prevent the emissions of more than 100 billion tonnes of CO2-eq. by 2050.
Carbon-negative measures such as better forest management and production of biochar will also be necessary to bring atmospheric concentrations of CO2 back down to safe levels, according to IGSD.
Surabi Menon, Hashem Akbari, Sarith Mahanama, Igor Sednev and Ronnen Levinson (2010) Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets. Environ. Res. Lett. 5 014005 doi: 10.1088/1748-9326/5/1/01400