Investigating the Climate Impacts of Urbanization and the Potential for Cool Roofs to Counter Future Climate Change in Los Angeles

The climate warming effects of accelerated urbanization along with projected global climate change raise an urgent need for sustainable mitigation and adaptation strategies to cool urban climates. Our modeling results show that historical urbanization in Los Angeles has increased daytime air temperature by 1.3 °C, in part due to a weakening of the onshore sea breeze circulation. We find that citywide adoption of cool roofs can meaningfully offset this warming by 0.9 °C, with residential cool roofs being responsible for 67% of the cooling. We also find that cool roof deployment could partially counter the local impacts of global climate change in Los Angeles. Assuming a scenario in which there are dramatic decreases in greenhouse gas emissions in the 21^st century (RCP2.6), mid- and end-of-century warmings are similarly reduced by cool roofs from 1.4 to 0.6 °C relative to current climate. Assuming a scenario with continued emissions increases throughout the century (RCP8.5), mid-century warming is also significantly reduced by cool roofs (from 2.0 to 1.0 °C). The end-century warming, however, is significantly offset only in small localized areas containing mostly industrial/commercial buildings where cool roofs with highest albedo are adopted. We conclude that city-wide adoption of cool roofs, with currently available technologies, on both residential and industrial/commercial buildings can play an important role in mitigating the urban heat island effect, and offsetting near-term local warming from global climate change. Large-scale reductions in greenhouse gas emissions are the only way of avoiding warming in the long-term, however. We further discuss the role of “cool photovoltaics” in climate mitigation and adaptation.