Heat Ready London Technical Report identifies 37 priorities for protecting the capital as 2026 delivers five heatwaves and preliminary data links extreme heat to 2,877 deaths across England in May and June alone
London faces annual economic damage of between £16 billion and £36 billion by the 2050s if the capital does not significantly accelerate its adaptation to rising temperatures, according to a major new technical report published today by the Mayor of London and London Councils.
The Heat Ready London Technical Report provides the detailed evidence base behind Heat Ready London — the capital’s first city-wide climate adaptation strategy, unveiled by Mayor Sadiq Khan in June 2026. It examines how extreme heat is already affecting Londoners’ health, homes, public services, infrastructure, and economy, and sets out 37 specific priorities for reducing the risk.
What the £36 Billion Figure Means
The report’s headline figure requires careful interpretation. The £36 billion annual damage estimate — equivalent to approximately three percent of London’s economy — is not a single projected bill but a composite assessment of economic losses that would accumulate across multiple sectors without further action.
The components of this estimated damage include:
- Lost working hours and reduced workforce productivity during high-temperature periods
- Increased pressure on NHS and emergency services from heat-related illness
- Disruption to businesses caused by infrastructure failure and worker absence
- Physical damage to essential transport, energy, water, and communications networks
- Costs associated with greater demand for cooling, emergency response, and recovery
The range between £16 billion and £36 billion reflects uncertainty in future economic growth projections rather than uncertainty about the underlying climate science — the physical risks are the same under both scenarios, but their economic value scales with the size of the economy they affect.
The Costs Already Being Recorded
The report makes clear that heat-related economic damage is not a future risk — it is already measurable in London’s current accounts.
Lost productivity linked to high temperatures is currently estimated to cost London £577 million annually. This figure alone accounted for approximately 90 percent of the estimated £1.5 billion total cost of London’s three heatwaves in 2022.
The 2022 heatwaves also produced specific infrastructure failures that illustrate the systemic nature of heat risk:
- Buckled rails caused widespread train cancellations and speed restrictions across the London network
- Two data centres at Guy’s and St Thomas’ NHS Foundation Trust failed during the extreme heat, disrupting patient care and requiring £1.4 million in unplanned emergency spending
- London’s water consumption rose by 50 percent during the peak heat period, placing significant strain on Thames Water’s supply infrastructure
These were not worst-case scenarios — they occurred during a heatwave that, while record-breaking at the time, is expected to become increasingly common under projected climate trajectories.
The 2026 Summer Context
The report is published against the backdrop of another exceptional summer. London broke temperature records in May, June, and August 2026 and had entered its fifth official heatwave of the year by mid-August — an unprecedented frequency for the capital.
Preliminary analysis from the UK Health Security Agency estimates that 2,877 heat-associated deaths occurred across England during May and June 2026 alone. This figure will be refined as fuller data becomes available, but it already indicates that the human cost of the 2026 summer is substantial.
The report highlights a counterintuitive finding about heat mortality risk: approximately 90 percent of heat-related deaths in London occur when temperatures are between 24°C and 32°C — a range that is far more common than the extreme peaks that attract public attention. This means heat risk is not primarily a problem of exceptional days but of sustained warm periods that accumulate health harm over time.
Evidence also indicates that Londoners aged between 45 and 65 face a greater risk of dying during hot weather than people of the same age nationally — a disparity that may reflect London-specific factors including urban heat island effects, housing stock characteristics, and the higher proportion of people living alone in the capital.
The 37 Priorities of Heat Ready London
The technical report underpins 37 specific adaptation priorities organised across six areas:
Buildings
Adapting homes and public buildings to remain cooler during high temperatures, including improved insulation, shading, and ventilation. The report notes that many of London’s older housing stock was built for heat retention rather than heat management — a design characteristic that becomes a health risk as summer temperatures rise.
Business
Supporting London’s commercial sector to adapt operations, protect workers during heat periods, and build resilience into supply chains and business continuity planning.
Emergency preparedness
Strengthening London’s coordinated emergency response to extreme heat events, ensuring that the health, social care, and emergency services response is better prepared than it was during the 2022 heatwaves.
Green space
Expanding access to shade, cooling green spaces, and drinking water across the capital, with particular focus on areas currently deficient in tree canopy and green infrastructure. London’s parks and green spaces are estimated to provide more than £90 billion in benefits over 30 years — approximately £27 of benefit for every £1 invested.
Health and care
Protecting the most vulnerable Londoners — older adults, young children, those with pre-existing conditions, and residents in poorly insulated homes — through targeted health and social care interventions during heat periods.
Infrastructure
Strengthening transport, energy, water, and communications networks to withstand higher operating temperatures, reducing the risk of the cascading failures seen during the 2022 heatwaves.
Who Is Most at Risk
Heat does not affect all Londoners equally. The report identifies specific groups facing disproportionate risk:
- Older adults, particularly those living alone or in care settings with poor ventilation
- People in poorly insulated homes, including those in the private rented sector with limited ability to make modifications
- Workers in outdoor or non-air-conditioned environments, including construction, agriculture, and delivery sectors
- Londoners aged 45-65, who face greater heat mortality risk than their national peers
- Residents in deprived areas with less access to green space, shade, and cooling resources
- People with pre-existing cardiovascular, respiratory, or renal conditions
The geographic dimension of heat inequality is also significant. London’s urban heat island effect — where the dense built environment retains heat more than surrounding rural areas — is most intense in inner London, where many of these vulnerable populations are concentrated.
The Economic Case for Acting Now
The report makes an explicit economic argument for early investment in adaptation. The estimated £90 billion in 30-year benefits from London’s green spaces against £27 of benefit per £1 spent illustrates a broader principle running through the document: the cost of adaptation is substantially lower than the cost of the damage it prevents.
This framing positions Heat Ready London not primarily as an environmental programme but as an economic risk management strategy — one that protects London’s productivity, public finances, and infrastructure investment from mounting climate-driven losses.
Deputy Mayor for Environment and Energy Mete Coban said the report provides the evidence and priorities needed to accelerate action, and that adapting homes and buildings, creating greener neighbourhoods, and strengthening infrastructure can protect vulnerable Londoners, reduce inequalities, and avoid greater costs in the future. He said delivery requires sustained investment and close collaboration across government, boroughs, businesses, and communities.
What Happens Next
The Mayor and London Councils are coordinating delivery of the 37 priorities across boroughs, health and care partners, emergency responders, infrastructure providers, businesses, financial institutions, and community groups.
The scale of the challenge means no single organisation can lead delivery alone. The report is designed to provide a shared evidence base that aligns action across sectors — ensuring that investment decisions by TfL, NHS trusts, housing associations, local authorities, and private businesses are shaped by a common understanding of where heat risk is greatest and what interventions are most effective.
The full Heat Ready London Technical Report is available through the Greater London Authority website.
