Extreme heat and climate change could cost London up to £36bn a year by the 2050s without further action, according to a new report from the Mayor of London and London Councils.

The Heat Ready London Technical Report underpins the capital's first city-wide heat adaptation plan, unveiled in June, and warns unmitigated climate damage could reach 3% of London's economy annually – between £16bn and £36bn depending on growth.

The figure spans lost productivity, healthcare pressures, business disruption and infrastructure damage, echoing impacts already seen during the 2022 heatwaves, which cost an estimated £1.5bn, £577m of that from lost productivity alone.

The warning follows another record-breaking summer: London saw temperature records broken in May, June and August, with a fifth heatwave declared by mid-August, while preliminary UK Health Security Agency data estimates 2,877 heat-related deaths across England in May and June 2026.

The report notes most heat deaths occur at moderate temperatures of 24–32°C, with Londoners aged 45–65 at particular risk.

Heat Ready London sets out 37 priorities covering buildings, green space, health and infrastructure, with officials stressing that early investment – such as green spaces delivering £27 for every £1 spent – could avert far greater costs later.

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The Mayor of London, Sadiq Khan, said: ‘The climate crisis is on our doorstep. It is already threatening Londoners’ lives, disrupting vital services and costing our economy hundreds of millions of pounds.’

‘No organisation can do this alone. I will continue working with boroughs, government, businesses, health services and communities to protect those most at risk and build a safer, greener and more resilient London for everyone,’ he added.

Professor Emma Howard Boyd CBE, Chair, National Heat Risk Commission and former Chair of the London Climate Resilience Review said: ‘I welcome the Mayor’s leadership in getting ahead of climate impacts rather than simply reacting to them. Heat Ready London builds on the London Climate Resilience Review, turning evidence into action. But delivering it at the pace these health, economic and national-security risks demand means giving mayors statutory climate-resilience duties and funding that matches their growing powers – reaching the communities at greatest risk first.’