Heat Ready London makes economic case to prepare for hotter summers

In the summer of 2022 London recorded temperatures above 40°C for the first time, leading to hundreds of heat-related deaths, damage to infrastructure, and the busiest day for the London Fire Brigade since the Second World War.

At the time it was considered an anomaly, but, over the next few decades, that level of heat is projected to become normal. It’s no longer a matter of whether London will face more extreme heat, but whether it is adequately prepared.

In 2026 we’ve had the hottest May on record, and the record for the hottest day in June broken multiple times under a rare red warning for heat, all contributing to what is likely to be the hottest summer on record. It was amidst these sweltering conditions that the Mayor of London Sadiq Khan, launched Heat Ready London, as part of Climate Action Week in June.

Working alongside the Greater London Authority and London Councils to develop the city-wide vision for London, it is clear that actions are needed to build resilience across six sectors: built environment, business and economy, emergency preparedness and response, green space and nature, health and care, and infrastructure.

A new study produced in support of Heat Ready finds London’s 2022 heatwaves are estimated to have cost the city £1.5 billion, That figure captures known impacts on health and wellbeing, lost productivity, impacts on infrastructure, school closures, and reduced activity as people stayed indoors. And yet, this figure is likely to underestimate the costs because not all the impacts in some sectors, including health, are well characterised.

It is a figure that should change how we think about heat. It is not just an environmental challenge or a public health concern, but an economic risk for one of the world’s leading cities.

Without action, climate change is projected to reduce London’s GDP by up to 3% in the 2050s (£16-36bn  annually depending on how London’s economy grows) according to the London Climate Resilience Review from 2024. As London’s population ages, impacts will intensify.

Analysis reveals one million London homes may be at high risk of overheating, with more than 1,300 schools, 60 hospitals and 351 care homes located in high heat risk areas. However, compared to other climate and economic challenges, heat risk has been under-prioritised.

Heat Ready London refocuses that priority, and the economic case for doing so is compelling. Retrofitting homes, one of the vision’s central pillars, is expected to cost up to £45bn over 25 years, roughly £2bn per year. It’s a significant sum, but it needs to be considered alongside the cost of inaction.

London is projected to have twice as many days above 30°C by 2050, and heatwaves will continue to inflict damage. There are already around one million London homes classified as being at high or very high risk of overheating.  This underlines the case for investment in climate adaptation, which begins to pay for itself relatively quickly. The choice is to invest steadily now or absorb repeated shocks that compound over time.

The benefits of action outweigh the costs, particularly if implemented early. Delay, by contrast, locks in higher mortality, places greater strain on public services, and allows productivity losses to escalate.

Retrofitting homes and buildings with relatively straightforward measures such as shading, ventilation improvements, and targeted cooling will reduce health risks, and the burden on healthcare systems and emergency services. This is particularly critical for older residents, infants, and those with pre-existing health conditions.

Similar considerations apply to critical infrastructure, as heat disrupts transport networks, strains electricity systems, and increases water demand. Impacts to infrastructure and buildings can close schools, disrupt businesses, and lead to services becoming less reliable. These should not be seen as isolated incidents, as taken together they ripple through the economy.

This makes it essential to strengthen infrastructure to maintain economic and operational continuity in a hotter climate, whether that’s power networks capable of handling higher cooling demand or resilient water supplies and networks.

Heat Ready London is not simply a public spending programme but represents a real opportunity for private capital. As we have seen from our own research into funding infrastructure last autumn there is growing appetite among investors for long-term, stable returns tied to sustainable infrastructure and retrofit programmes. Heat resilience can fit that profile if the right financial frameworks are in place.

Our work alongside Pengwern Associates has explored potential funding and financing models ranging from green bonds for green infrastructure, to blended finance retrofit programmes, where upfront investment can be repaid over time.

With the right policy support, including risk-sharing from central and local government, private finance can play a major role in scaling delivery. Given the size of the challenge, public finances alone cannot deliver the transformation required, and nor should they need to, when action delivers both public and private benefits.

There is also a broader return on investment as a more heat-resilient London is a more liveable city which attracts talent, supports businesses, and remains competitive globally. Measures such as improved public spaces, access to drinking water and public toilets, and better urban design make the city more inclusive and more productive.

The debate about managing heat in London should not focus solely on affordability but must also consider value. We are already paying for heat through disrupted services, strained healthcare systems, lost economic output, and avoidable loss of life. The question is whether we continue to pay for that reactively, at increasing cost each year, or choose to invest proactively in resilience.

The evidence suggests that investing now reduces long-term costs. It also saves lives and creates opportunities for innovation and green jobs along the way. Extreme heat is a big test for a globally important city like London, but we have the data, the tools, and the economic case to act.

This article was first published in July by New Civil Engineer