Britain’s Ordnance Survey (OS) has found over eight out of 10 cities in the UK are already highly vulnerable to urban heat islands, and almost two thirds are set to reach severe heat levels by 2100.
Among those expected to warm the most are Leicester, Exeter, Nottingham, Brighton and Bristol. The City of London has the least effective natural cooling of any UK city due to its high-rise buildings and limited green space, trees and water.
By comparison, Milton Keynes has the lowest built-environment vulnerability in England and the most effective natural cooling of any city in the OS analysis with 46 square kilometers of natural surfaces. In comparison, Portsmouth has the worst OS heat index - a position it will retain for the remainder of the century.
Urban heat islands form where dense buildings, roads and hard surfaces absorb heat from the sun and retain it overnight because tall buildings and narrow streets reduce wind speeds that would otherwise carry heat away, and a lack of trees and water sources eliminate the natural cooling effects of shading and evaporation.
OS analysis has found 59, or 83 percent, of Britain's cities are already highly vulnerable to urban heat, with the remaining 12 (17 percent) classed as moderately vulnerable. By 2040, rising summer temperatures are projected to push every city into the high vulnerability category.
An estimated 2,877 heat-associated deaths were recorded in May and June of 2026 due to the impact of urban heat islands. A study commissioned in support of Heat Ready London, the Mayor of London's heat resilience initiative, estimated London heatwaves in 2022 cost £1.5 billion in productivity losses, health impacts, education disruption, energy demand and transport and emergency services delays.
"These findings matter because cities are where millions of people live, work and spend their everyday lives. Extreme and sustained heat can affect people’s health and wellbeing, [and] how comfortable our homes and workplaces are,” commented OS CEO Nick Bolton.
https://www.ordnancesurvey.co.uk/
