City Hall estimates that London’s heatwaves in 2026 may have cost the capital around £2.5 billion in lost productivity, using temperature readings and earlier economic research to indicate the possible scale of the impact.
The figure is an estimate of reduced economic output, not a measured total of losses reported by London businesses. City Hall also presents a roughly £25 billion cost over ten years if summers as hot as 2026 were repeated. That is an illustrative scenario, not a forecast of the weather or of what London will definitely lose.
Mayor of London Sadiq Khan is using the analysis to argue for investment in protection against extreme heat as well as action to reduce emissions. He is representing London at the COP31 climate conference in Antalya, Türkiye, where he has called for support for cities facing hotter conditions.
How the estimate was made
City Hall drew on research into the economic effects of London’s 2022 heatwaves, updated it using temperature data for summer 2026 and adjusted the calculation for inflation. It applied an estimated daily productivity cost to 34 days on which the temperature exceeded 28°C at the City Hall location.
The 34 days are part of the calculation, rather than a claim that every London neighbourhood recorded the same temperature or that all 34 days were separately designated official heatwave days. The resulting figure represents a potential loss of output; it does not measure the accounts of individual employers, or capture the full health and social consequences of heat.
The underlying calculation used historical estimates of heat-related losses in gross value added, a measure of economic output. It considered how effects could vary across sectors, including differences in the kind of work people do and the extent to which labour can be substituted with equipment. Its central calculation also assumed that some adaptation measures were in place, rather than treating all workplaces as equally exposed.
For the 2022 heatwaves, the underlying model estimated about £1.3 billion in lost productivity. It also allowed for a range of possible outcomes, reflecting variation in historical daily costs. That earlier range does not quantify the uncertainty around the new £2.5 billion estimate.
The same model estimated a broader £1.5 billion economic and social cost for the 2022 heatwaves, including impacts beyond productivity. It used 2024 prices. That wider total is not directly comparable with the new productivity-only estimate and is not an additional cost to be added to it.
What the ten-year figure means
To illustrate a possible future, City Hall multiplied its annual estimate by ten. The scenario assumes that summers over the coming decade are as hot as, or hotter than, the summer of 2026. It does not allow for future inflation.
The arithmetic is intended to show the consequences of repeated hot summers on that basis. It does not establish how likely such a sequence is, how temperatures will vary from year to year, or what changes in buildings, working practices and the economy might do to future losses. Nor is it an estimate of everything heat could cost health services and households.
Pressure beyond workplaces
Heat can disrupt work indirectly as well as making working conditions harder. The 2022 London model estimated that school closures associated with the heat led to nearly 60,000 lost working days for parents and about £9.4 million in lost earnings. The calculation relied on assumptions about how school disruption affected parents; it was not a count of every parent who took time off.
London Ambulance Service said it attended 300 heat-exposure incidents between June and August 2026, more than three times its five-year summer average. It also reported its busiest summer on record for 999 calls. Extreme heat added to the pressure, but the overall volume of calls cannot all be attributed to hot weather.
Heat Ready London, a city-wide plan produced by the Mayor and London Councils, sets out priorities that include reducing overheating in homes and essential public buildings, protecting frontline workers and providing more shade. Its approach involves boroughs, health services, emergency responders and infrastructure providers.
Those priorities are not the same as a completed programme of works. Making existing buildings cooler can require changes to shading, ventilation or other features, while transport and other services have their own resilience needs. City Hall says delivering the wider plan will require public funding, private investment and support from national government.
The productivity estimate gives the Mayor a numerical basis for that investment argument. Its limitations are equally important: it models a possible loss from the conditions recorded at one location, while the ten-year figure repeats that estimate under a stated assumption. Neither should be treated as a bill already paid or a certainty about the next decade.
