Simple trick could cut city temperatures by 3.6F, London study suggests

Painting London’s rooftops white could help reduce outside temperatures by up to 2 degrees Celsius, according to a new study examining the most effective ways to cool the UK’s capital.

Climate change is expected to lead to warmer and drier summers in Londonand the average summer day will be around 5.4 F (3 C) warmer by 2050. New findings suggest painting roofs white could be one way the British city could respond to the problem.

“We have extensively tested a range of methods that cities like London could use to adapt to and mitigate rising temperatures. We found that cool roofs are the best way to keep temperatures down on extremely hot summer days,” said the lead author. Oskar Broussea lecturer at University College London specializing in urban meteorology and environmental modeling, said in statement“Other methods had various important side benefits, but none were able to reduce external urban heat to nearly the same level.”

Like many large cities, London is in a precarious position as global temperatures rise because it is built to absorb heat. Dark buildings, tarmac roads and underground rail networks make it an “urban heat island”, where urban areas are significantly warmer than the surrounding rural areas. City planners are now looking at ways the city can adapt to ever-rising temperatures.

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In a study published July 4 in the journal Geophysical Research ListsScientists have been looking for the most effective ways to cool the city in the face of climate change. They analyzed the impact of various strategies, including adding solar panels to roofs, painting roofs white or covering them with a reflective coating (known as “cool roofs”), covering roofs with vegetation, planting more vegetation at street level and massively deploying air conditioning.

By 2050, summer temperatures in London are predicted to rise by 5.4 F (3 C). (Photo source: SHansche/Getty Images)

To do this, they created a 3D computer model of London and ran 11 different climate simulations using different techniques to cool the city on the two hottest days of summer 2018, when temperatures reached 95 degrees Fahrenheit (35 degrees Celsius). All simulations assumed widespread adoption of each technique.

The results showed that “cool roofs” painted white or covered with a reflective coating, when widely adopted, lowered outside temperatures by an average of 2 F (1.2 C), and in some areas by 3.6 F. Extensive street vegetation and solar panels caused temperatures to drop by about 0.5 F (0.3 C), while green roofs had a negligible effect. Air conditioning may keep homes cool, but it raises outside temperatures by as much as 1.8 F (1 C) in central London.

The study authors wrote that the study had several limitations, including that the researchers only took into account outdoor temperature and did not consider the costs or benefits of other interventions, such as increasing biodiversity and lowering indoor temperatures.

“Despite these limitations, we expect our results to be at least indicative and to indicate which interventions could have the greatest cooling effect in London on hot summer days,” they wrote.