How can London adapt to hotter summers?

Climate change is pushing temperatures higher and, like most cities, London is full of hard surfaces that absorb heat in built-up areas. As we expect hotter and drier summers, what is being done to reduce overheating and protect Londoners?

By Lauren Hurrell

After a cold winter and wet spring, the summer heat returned to London in June. However, a season that typically sees the UK capital thrive with outdoor activities has instead brought fresh warnings about heatwaves and safety guidelines. 

Is extreme heat the new norm for London summers, and if so, how can the city adapt to become more resilient to climate change?

London in summer heatwave
A digital billboard is seen displaying the hot temperature in central London. The temperature rose to 30°C in London in the first heatwave of the year and forecasters warn more extreme weather is to come. (Photo by Hesther Ng/SOPA Images/LightRocket via Getty Images)

Climate change is turning up the thermostat in cities across the world, but some are more readily adapting to heat than others. London’s hottest temperature was recorded just last year, reaching 40.2°C on 19 July 2022. It was a summer of extreme heatwaves all across the UK, which saw the government issue a health warning as severe as a national emergency for the first time.

While warm days of alfresco dining in the sun might seem like a quaint perk of cosmopolitan living, the high-hitting temperatures present a health concern and a threat to the functioning of a city that was not planned with intense heat in mind.

The population is also rising, increasing city density and contributing to urban heat islands, which can increase temperatures in London by up to 10°C compared with neighbouring areas, as the sun’s rays are absorbed through hard surfaces and then released as heat.

Heat management strategies are therefore critical for keeping London cool if it is to adjust to this new normal, as a city that was not built for record-breaking temperatures becoming the norm.

Will London hit 40°C this summer?

Whether temperatures will reach 40°C again this year is not yet known, but it’s possible, and more heatwaves are expected across the UK. Last year’s heatwave severely impacted people’s health, transport, emergency services and power supplies all over the country, and London needs to brace itself for more.

High temperatures impact all sectors at a serious cost if stringent measures aren’t taken.

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During last year’s heatwave, Transport for London experienced high levels of customers and staff taken ill; speed restrictions on the Tube and rail; £8m loss of revenue; construction work suspended; and points, signalling and track circuit failures. Like many sectors, it aims to better manage risks in the future for more expected heatwaves.

For the elderly, young people, individuals with health conditions or chronic illness and people experiencing homelessness, the impact is far worse.

Keeping Londoners cool

In setting targets for the city to reach net zero by 2030, Mayor of London Sadiq Khan identified heat as one of the risks from extreme weather that will have greater impacts in the future. The Mayor’s Business Climate Challenge (BCC) aims to decarbonise businesses, improve energy efficiency and minimise the effects of heat islands. Emission zones and the adoption of EVs will also reduce the contributions of heat in many areas, from traffic to heat islands, while minimising air pollution in dense city areas.

The mayor is also working with London’s boroughs, public health officials, universities, community groups and others to research and reduce the risk of heat in the city. The London-specific Severe Weather and Natural Hazards Framework has been updated to include a focus on how we respond to and manage heat risk from heatwaves.

Additionally, the government’s Heat Health Alert Service outlines five levels of alert to be issued when temperatures pass certain thresholds in the summer months. The service recommends a series of steps to reduce health risks from prolonged exposure to severe heat for the NHS, local authorities, social care and other public agencies, professionals working with people at risk, and individuals and local communities.

This will put a strain on services as they struggle to handle the increased demands of care during hot periods. There is also a greater need for the UK government to outline how it accounts for these risks in its NHS funding settlement and how this will be considered going forward, to ensure services are prepared and safely well staffed to meet demands.

How hot will London summers be in 2050?

By 2050, London will expect to see wetter winters, drier summers and hotter temperatures, with an average increase of around 3°C.

London’s heat often tends to feel drier than other locations due to a lack of humidity in the air in urban areas. This comes down to there being less vegetation and the impact of heat islands caused by dark asphalted or concrete surfaces.

Nature does provide us with a natural source of moist air, which can be recreated using electricity to evaporate water, but it’s an incredibly expensive process, costing an estimated €500,000 per hectare. Increasing biodiversity in cities such as trees, plants and grass would help to regulate temperatures.

Trees aren’t only for cleaning the air, they also reduce surface and air temperatures by providing shade, with shaded areas being around 11–25°C cooler than peak temperatures of exposed areas or materials.

A greener, more resilient London

As a densely populated city, urban green infrastructure will help to minimise heat risk to reduce the negative impact seen last year, to make London safer and better adapted to managing heat.

Nearly 18% of London is covered by its 3,000 parks, more than the area of the city covered by railways and roads combined. The mayor aims to increase this to 50% by 2050, which will aid in significantly reducing overheating, through opening more parks, roof gardens and open spaces of foliage to absorb and displace heat in the hard city. This process, called evapotranspiration, adds moisture to the air like natural air conditioning.

The obvious follow-up question is why can’t air conditioning be installed all over the city? Installing air conditioning would be incredibly expensive and require significant energy usage, only contributing more negative impacts to climate change. Instead, grey infrastructure can take heed of better insulation and heat management strategies, such as using reflective surfaces on buildings to reduce the need for air conditioning inside.

While there are some limitations to this, including limited resources and reflecting heat to other surfaces, the installation of reflective surface technologies can redirect sunlight away to be absorbed by vegetation to reduce the effects of heat islands.

“The treatment of overheating at [the] design stage is fundamental in increasing the resilience of buildings in hot events, now and in the future,” says the CIBSE (Chartered Institution of Building Services Engineers).

With the implementation of green and grey infrastructure in London, it is hoped that heat will become more manageable as we see higher temperatures, while aiming to be greater prepared to meet net-zero targets.

[Read more: The cities adapting best to climate change]

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