Heatwaves Could Cost London £25bn in a Decade, Mayor Warns

This summer’s heatwaves cost London around £2.5 billion in lost productivity, and if summers like it become the norm the bill could pass £25 billion over the next ten years, City Hall estimated on Wednesday 11 November. That is more than the Mayor’s entire annual budget for London.

The Mayor of London, Sadiq Khan, is taking the figures to COP31, the United Nations climate conference in Antalya, Türkiye. City Hall says he will be the first Mayor of London to speak at the World Leaders’ Summit, a slot usually kept for heads of state and government leaders.

What it meant in Haringey

Some of the sharpest heat this summer was felt by people working in it. Arriva bus drivers at garages including Tottenham and Wood Green walked out over temperatures in their cabs, and the dispute only ended in September when drivers accepted a deal to fit air conditioning to Arriva London North buses by May 2027 (our report on the settlement).

Protecting frontline workers is one of the priorities in Heat Ready London, the plan City Hall produced with London Councils and published this summer. It also sets out reducing overheating in homes and essential public buildings and creating more shade, and brings together health services, emergency responders, transport providers and utilities to improve how the capital prepares for and responds to extreme heat.

Making buildings cooler will cost money. City Hall says public funding, private investment and support from national government will all have a role to play. Locally, community groups have until 11.59pm on Sunday 29 November to bid for up to £50,000 from Haringey’s Community Carbon Fund (how to apply).

What the heat cost

City Hall’s estimate draws on research into London’s 2022 heatwaves, updated with this summer’s temperature data and adjusted for inflation. High temperatures make it harder for people to work effectively, which is where the lost productivity comes from.

Families felt it too. Earlier research found that heat-related school closures during the 2022 heatwaves cost parents nearly 60,000 working days and an estimated £9.4 million in lost earnings, according to the Mayor’s office.

The emergency services had one of their busiest summers on record:

• London Ambulance Service had its busiest summer on record. Crews attended 300 heat-exposure incidents between June and August, more than three times the five-year summer average.
• London Fire Brigade firefighters and control officers responded to nearly 100,000 emergency calls between May and August.

Jason Killens, chief executive of London Ambulance Service, said: “This was a record-breaking summer for both the UK and London Ambulance Service. As the capital sweltered, our colleagues across the organisation worked tirelessly to respond to more 999 calls and Category 1 incidents than during any previous summer.”

He added: “We are now preparing for winter and already planning for next summer, including how we put additional ambulance crews on the road to respond to the surge in demand that extreme weather brings and ensure the sickest patients continue to get the care they need.”

London Fire Commissioner Jonathan Smith said investment from the Mayor had paid for new training and equipment to help the Brigade predict, prevent and tackle wildfires. “As the impacts of climate change become more frequent and severe, the risk of wildfires across the capital will continue to grow,” he said. “It is critical that the fire and rescue service is adequately resourced to enable us to continue to respond and keep our communities safe.”

The death toll

Research from Imperial College London and the London School of Hygiene & Tropical Medicine, cited by City Hall, estimates that more than 50,000 people died from heat-related causes in European urban areas this summer, with around two-thirds of those deaths attributed to human-induced climate change. Imperial College London also estimates there were more than 4,000 excess deaths across 135 urban areas in the UK this summer.

Dr Tom Coffey, the Mayor’s health adviser and a London GP, said: “Extreme heat now presents the greatest risk to health from climate change in the UK, and as a GP, I’ve seen first-hand that its impacts are widespread, not just on those we traditionally think of as vulnerable, such as those with mental and physical health conditions, but any of us.”

What the Mayor will tell world leaders

In his speech to the World Leaders’ Summit, Sadiq Khan is expected to say: “Climate disaster is no longer the stuff of some distant dystopia. It’s killing people, harming communities and impacting our economies right now. And failing to protect ourselves from the perils we face, or prepare ourselves for worse to come, would be a dereliction of duty.”

On the cost of acting, he is expected to say: “The climate sceptics argue that these investments are unaffordable. But the only thing we cannot afford is to do nothing. Because, even if you can see past the devastating implications for human health, the long-term economic impact of extreme heat alone will be astronomical. If the scenes we saw this summer became the standard, it could cost London’s economy more than £25 billion over the next ten years.”

City Hall points to work already done: early warning systems for heat and air quality, more than 640,000 trees planted across London under the current Mayor, more than 2,000 football pitches’ worth of green space created or improved, and work to clean up rivers and create safe swimming sites. Through the C40 network of almost 100 cities, which the Mayor co-chairs, London aims for every member city to have an early warning system by the end of 2027.

Emma Howard Boyd, chair of the National Heat Risk Commission, said: “This summer’s heatwaves showed extreme heat is a defining risk to our health, our economy and the public services we rely on. The capital has shown what practical preparation looks like, but no city can do this alone. The UK needs a heat ‘circuit breaker’: a national response that protects people now and invests in homes, workplaces and public buildings fit for a hotter future.”

The figures come from a Mayor of London press release issued on 11 November 2026.