Extreme heat is the silent killer of climate change: How can cities beat it?

As fires rage and droughts blight communities around the world, cities have been sweating. Temperatures have reached record highs in Paris (France), London (UK), and Lisbon (Portugal), and have topped 50°C in Nawabshah (Pakistan), Phalodi (India), and Basra (Iraq).

There is agreement among experts that heatwave deaths are preventable. But extreme heat led to 1,700 “needless” deaths in Spain and Portugal during the July 2022 heatwave. A recent study of nine countries found that 356,000 deaths were linked to extreme heat in 2019. Temperature increases are also projected to reduce working hours by 2.2% and global GDP by USD 2.4 trillion by 2030, due to the dangerous working conditions caused by extreme heat.

Feeling the heat sink

The effects of extreme heat are frequently more severe in cities. Cities generate “urban heat islands” due to population density and a concentration of structures and materials that retain heat and a lack of natural surfaces that dissipate it.

The centres of London and Paris, for example, regularly record temperatures of around 4°C higher than rural surroundings at night. In Athens, this difference can reach 10°C during the summer. In Sydney (Australia), surface temperatures of the built environment can grow up to 16°C warmer in the sun than in shaded areas.

Surface temperatures in major European cities were much warmer than surrounding rural areas during 2019 heat wave due to their density and built environment

The poor often suffer most from extreme temperatures.

The poorest neighbourhoods are often higher density, and lack shade, green space and ventilation, leading to higher peaks. During heatwaves, governments issue public health warnings advising citizens to stay home and away from the sun, but workers who lack flexible schedules or the ability to work remotely do not have this luxury.

Access to affordable energy also comes into play. City medical officials in Portland (US) reported that many of the 64 residents who died from the 2021 heatwave were found in their homes without a fan or air conditioner.

The hottest neighbourhoods in Los Angeles, California are also the poorest

The melting city

Rising temperatures do not only affect people, but also key infrastructure. In the UK, Luton airport restricted flights after its runway melted during the July 2022 heatwave. Fort Worth, Texas (US) has seen a drastic increase in water main breaks due to extreme heat drying out and shifting the ground, depriving residents of access to water.

In China, increased use of air conditioning during heatwaves has overloaded power grids and caused blackouts. Conventional pavement materials can reach temperatures up to 67°C, and roof material up to 90°C.

Heat beaters: how are cities cooling off?

Cities can implement cost-effective measures to help tackle the heat. The city of Los Angeles (US), 10% of which is blanketed in black asphalt, is covering its roads with a white-coloured sealant with high reflectivity. This is reducing temperatures by a range of 10-23°F.

New York (US) has covered more than 500,000 square metres in heat-absorbent roof material with reflective coating, reducing emissions from cooling by nearly 3,000 tonnes per year. By reducing the need for cooling buildings, such initiatives also assist the decarbonisation of buildings and transport, combatting climate change.

Cities can also make fundamental changes to their design, trading out the concrete jungle for natural green space to cool down. Paris (France) is “greening” the congested Champs-Elysées, swapping car traffic for trees, pedestrian and cycling space, as part of a wider green transformation of the city.

Through its “City Champions for Heat Action” initiative, the Adrienne Arsht-Rockefeller Foundation Resilience Centre is working with Freetown (Sierra Leone) and Athens (Greece) on innovative ways to reduce temperatures as well. Freetown is implementing “Freetown the Treetown”, an initiative to plant one million trees to provide shade. Athens is restoring an ancient aqueduct to irrigate newly created green spaces that will cool down the city. Athens recently appointed Europe’s first Chief Heat Officer to address the issue directly.

“Hotspot” cities must keep it cool 

Cities’ exposure to extreme temperatures will nearly triple in the coming decades. By 2070, 1.6 billion urban residents will be heavily affected by heat, exacerbating existing challenges and vulnerabilities. But every heat-related death is preventable. Cities must take action now if we are to beat the heat.

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