Salem, Oregon – November 14: Andrew Koyaanisqatsi installs solar panels on his home hot water system … [+]
To protect an entire city’s residents from the summer heat, simply painting all its roofs white or using a reflective coating could reduce outdoor temperatures by 1.2 degrees Celsius across the city, according to a new study published in 2010. Geophysical Research Letters. Additionally, widespread rooftop solar panels could lower temperatures by 0.5 degrees.
“After a comprehensive test of multiple methods that cities like London can use to adapt to and mitigate global warming, we found that cool roofs are the best way to reduce temperatures on the hottest summer days. While other methods offered a range of important side benefits, none were able to reduce outdoor heat in urban areas to anywhere near the same levels,” lead study author Oskar Bruce from the Bartlett School of Environment, Energy and Resources, University of London, said in a press release.
Most cities are concrete jungles, with natural land covered primarily by pavement, buildings, and other asphalt/concrete surfaces that absorb and retain heat, creating a common phenomenon known as the “urban heat island.” This makes urban areas significantly warmer than the countryside, and each summer the urban heat island makes city dwellers more susceptible to heat exhaustion and heat stroke.
“Passive urban cooling strategies that are often proposed to directly reduce temperatures include increasing urban vegetation, incorporating vegetation into roofs (green roofs), or introducing highly reflective roofs known as cool roofs, which can be constructed from a variety of materials (e.g., concrete, metal, or single-ply membranes),” the authors write in their study. “Roof modifications can reduce indoor temperatures and cooling needs within buildings. When implemented at a city scale, they can also reduce outdoor temperatures and associated heatstroke mortality.”
Studies have shown that green roofs make no contribution to overall city cooling when compared to cool roofs and rooftop solar panels.
“Although rooftop photovoltaic panels are primarily thought of as a source of electricity, they can also be considered as a passive-active strategy to influence outdoor and indoor temperatures by increasing the roof’s albedo (the proportion of light reflected by a surface) and converting incoming solar radiation into electricity that can be used to run air conditioning systems,” the authors explain. “The impact of interventions at a city scale is reduced when applied to smaller areas or fewer buildings. In the case of cool roofs, we see a larger impact when applied to low-rise residential areas in London, but we have already found that when applied to mid-rise buildings in the city center, they can reduce temperatures in surrounding residential areas.”
In 2023, the UK reported 2,295 deaths believed to be attributable to heatwaves in the summer of England. Heatwaves are known as one of the most deadly extreme weather events globally. Climate scientists say the summer of 2023 was the hottest in human history. Studies have linked heatwaves to rising air pollution levels. Prolonged exposure to heat can make people more susceptible to death from cardiovascular disease, chronic kidney disease, and respiratory distress.
