Continued heatwaves in London could cost capital more than £25 billion over next decade, Mayor warns as he urges global action at COP31

• City Hall estimates continued heatwaves in London could cost capital more than £25 billion in lost productivity over next decade, as analysis reveals London’s 2026 heatwaves alone cost around £2.5 billion
• Health impacts similarly stark as more than 50,000 people died from heat-related causes in European urban areas this summer.
• Recent figures from Imperial College London estimate that there were over 4,000 excess deaths across 135 urban areas in the UK this summer, following unprecedented temperatures.
• Representing London at COP31, Sadiq will become the first Mayor of London to speak at the World Leaders’ Summit as he calls for investment to protect lives and livelihoods as cities face hotter summers, warning that, if we do nothing, the long-term economic costs of the climate emergency will be “astronomical”.
• Mayor highlights action to make London more resilient, including cooler buildings, more shade and greener spaces

The Mayor of London, Sadiq Khan, is calling directly on global leaders to step up action to tackle the climate emergency and protect cities from extreme heat, as new City Hall analysis estimates that London’s heatwaves could cost the capital more than £25 billion in lost productivity over the next decade – more than the Mayor’s entire annual budget for London.

Representing London at COP31, the United Nations Climate Conference in Antalya, Türkiye, Sadiq will warn that rising temperatures are already taking a heavy toll on people’s health, businesses and public services, with thousands of vulnerable people also losing their lives to heat-related causes.

The historic gathering will see Sadiq become the first Mayor of London to speak at the World Leaders’ Summit at COP. He will directly address global leaders from the main stage, an honour usually reserved for Heads of State and government leaders.

As elected Mayor of London and Co-Chair of the C40 network of global cities, the Mayor will urge leaders to match the scale of the challenge with investment, highlighting how cutting emissions and protecting people from climate change can strengthen economies as well as improving public health and saving lives. 

The new analysis, which estimates the 2026 heatwaves cost the capital around £2.5 billion in lost productivity, underlines the economic consequences of extreme heat, as high temperatures make it harder for people to work effectively. It draws on research into London’s 2022 heatwaves, updated using this summer’s temperature data and adjusted for inflation.[1] 

For working families, the impact can extend beyond the workplace. Earlier research found that heat-related school closures during the 2022 heatwaves resulted in nearly 60,000 lost working days for parents and an estimated £9.4 million in lost earnings.[2] 

This summer also showed the pressure extreme heat places on London’s emergency services. London Ambulance Service experienced its busiest summer on record, with extreme heat driving up demand. Crews attended 300 heat-exposure incidents between June and August, more than three times the five-year summer average.[3] 

The consequences are being felt across the globe. Research from Imperial College London and the London School of Hygiene & Tropical Medicine 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. Recent figures from Imperial College London estimate that there were over 4,000 excess deaths across 135 urban areas in the UK this summer, following unprecedented temperatures. [4] Additional figures from The Lancet estimate that heat contributed to the deaths of over 700,000 people globally in 2023, and the frequency and intensity of extreme heat in 2026 mean the death toll is likely to exceed that figure this year – as a Super El Niño causes fires, flooding, and storms around the world. [5] 

Attending the Early Warnings For All event at COP31, convened by the UN Secretary-General and gathering together Heads of State, multilateral development banks, and philanthropic leaders, Sadiq will argue that these findings make the case for urgent action to protect communities from the heat they already face, alongside continued efforts to tackle the causes of the climate crisis.

In his speech to the World Leaders’ Summit, the Mayor of London 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.” 

In London, the Mayor is working with boroughs and other partners to prepare the capital for hotter summers and protect those most at risk. London has already taken world-leading action, putting in place comprehensive early warning systems for heat and air quality, and under the Mayor’s leadership more than 640,000 trees have been planted across the capital, shading our streets from the summer sun.

More than 2,000 football pitches’ worth of green space has also been created and improved, providing natural drainage to prevent flooding, and the Mayor has prioritised cleaning up London’s rivers and creating safe swimming sites for Londoners to cool off.

Heat Ready London, produced with London Councils and published this summer, is a plan that takes things further - setting out priorities including reducing overheating in homes and essential public buildings, protecting frontline workers and creating more shade. Greener spaces can also help communities find relief from high temperatures. 

The work brings together health services, emergency responders, transport providers and utilities to improve how London prepares for and responds to extreme heat. 

Making buildings more resilient will require investment. Public funding, private investment and support from national government will all have a role to play.[5] 

Speaking at the summit, the Mayor is expected to warn:

“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.”

Through C40, London is also sharing experience with other cities responding to the climate crisis. Barcelona combines climate shelters with energy advice services to help residents facing extreme heat and energy poverty. Los Angeles is involving workers and communities in shaping its move away from dependence on fossil fuels.[6] 

At COP31, the Mayor will call for cities to receive the funding and support they need to go further, protecting communities today and building stronger economies that can withstand the hotter summers ahead, at the same time as taking strong action to tackle the root causes of the climate crisis. 

Sadiq is expected to add: 

“Right now, there are billions of people around the world without basic protections from climate catastrophe, forced to count the cost of a crisis they did not create and do not control. That’s why, through C40 cities – a global network of almost 100 cities with a population close to one billion people -  we’re working to ensure that all our members have early warning systems by the end of 2027. But these systems can never be a substitute for tackling the root causes of the climate crisis.

“Contemplating the sheer scale of the challenge ahead, it can be hard to stay optimistic. But we owe it to the world to hold on to hope. Indeed, rather than sacrificing the planet and its people on the altar of passivity and pessimism, we must follow the example of hope set by our cities – pushing harder than ever towards net zero, even as we adapt to the reality of a warmer world. And we must do so in the belief that a fairer, greener, healthier, and more prosperous future is possible for everyone.”

London Fire Commissioner, Jonathan Smith, said: “This summer was one of the busiest on record for the Brigade, with firefighters and Control Officers responding to nearly 100,000 emergency calls between May and August.

“In preparation for the heatwaves of 2026, we built on lessons learned from previous years to strengthen our resilience and improve our response. Thanks to investment from the Mayor of London, we have introduced new training and equipment to help us better 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. It is critical that the fire and rescue service is adequately resourced to enable us to continue to respond and keep our communities safe.”

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. I welcome the Mayor taking London's experience to COP31. 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.” 

Dr Tom Coffey OBE, Mayoral Health Adviser and London GP, said: “The last six months have shown us what lies ahead if we don’t take global action to tackle the climate crisis. In London and other cities across Europe, we saw the devastating human consequences of extreme heat, as more than 50,000 people are estimated to have died from heat-related causes in European urban areas this summer. Our emergency services saw unprecedented demand, with increased callouts to Londoners struggling in the heat.

“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. 

“This makes the work we are doing with health services, local government, communities and partners through the Mayor’s Heat Ready London vision even more important. The time to act is now. We must work together – across our cities and globally too – to tackle the root cause of the climate crisis, ensure our health systems are resilient, and protect the lives of our populations.” 

Jason Killens KAM, 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.

“The extreme heat placed additional pressure on our services, but thanks to the extra resources and planning we put in place, we were ready to support those affected.

“I would like to thank all of our people for their incredible efforts over the warmer months. Their professionalism, dedication and resilience have helped keep Londoners safe throughout a challenging summer. 

“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. We are also cutting our emissions by introducing more electric vehicles, creating the UK’s largest electric ambulance fleet.”

Lilli Matson, Chief Safety, Health and Environment Officer at TfL, said: “As hot summers and heatwaves become more common and no longer a rare exception, we know that the impacts of such extreme weather will only continue to increase unless we work together to take action. This is why we are working with other agencies, including Network Rail, the Greater London Authority and others to develop a coordinated approach and manage the adverse impact of higher temperatures on our network, from track and road surface resilience to customer comfort and staff safety.

“Alongside this, we're continuing to invest in making London's transport network more resilient and comfortable for customers. This includes introducing new air-conditioned trains on the Piccadilly line and DLR, expanding our fleet of air-conditioned buses and improving cooling and ventilation across the wider network. This work complements the measures we already have in place, such as almost 25,000 street trees providing shade, and wider action including our transition to renewable energy. 

“We are committed to playing our part in making London a climate-resilient city, ensuring that the capital’s transport network can operate safely and reliably as we continue to adapt to climate change.” 

Dr Alan Dangour, Director of Climate & Health at Wellcome, said: “Climate change is bringing hotter summers and more frequent heatwaves, and cities are where people are most exposed to the danger. Without action, the health impacts of climate change will only intensify - with groups like pregnant women, children, outdoor workers and older people most at risk. The Mayor’s call to action at COP31 must galvanise world leaders to act together to save lives and keep people safe.”