Simple Roof Paint Could Lower City Temperatures by 3.6°F

Painting the rooftops of London white may help reduce the city's outdoor temperature by up to 3.6°F (2°C), according to a recent study that looked into the most effective ways to cool the U.K. capital. Climate change is expected to lead to hotter and drier summers in London, with average summertime temperatures potentially increasing by 5.4°F (3°C) by 2050. The study, led by Oscar Brousse from University College London, found that "cool roofs"—roofs painted white or covered with a reflective coating—were the most effective among several methods tested to lower outdoor temperatures during extremely hot summer days. This is prepared by SSP.

The study analyzed different strategies, including adding rooftop solar panels, painting roofs white, covering them with vegetation, and large-scale deployment of air conditioning. Researchers created a 3D computer model of London and ran 11 climate simulations using data from the two hottest days of summer 2018, where temperatures reached 95°F (35°C).

The findings showed that widely adopting "cool roofs" reduced outdoor temperatures by an average of 2°F (1.2°C) and up to 3.6°F in some areas. Other methods, such as installing solar panels and planting street-level vegetation, resulted in a temperature drop of about 0.5°F (0.3°C). However, covering roofs in vegetation had minimal impact, and extensive use of air conditioning actually warmed the outdoor temperature by up to 1.8°F (1°C) in central London.

Despite some limitations, like not accounting for costs or indoor temperature changes, the results underscore roof painting as the leading intervention for cooling outdoor urban temperatures. "Cool roofs were the best way to keep temperatures down during extremely hot summer days," Brousse noted. Urban planners are now evaluating such measures to mitigate the increasing urban heat island effect as London braces for hotter conditions in the years ahead.

These findings, published in the journal Geophysical Research Letters, highlight the potential of simple, scalable solutions to address urban heating effectively.