As global temperatures rise, Britain's cities are being forced to reckon with a future shaped not just by distant climate projections, but by the concrete and asphalt beneath their own feet. New research from Ordnance Survey, the Met Office, and 4 Earth Intelligence has mapped heat vulnerability across all 71 chartered cities in England, Scotland, and Wales, revealing that by 2040 every one of them will reach high vulnerability — and by century's end, nearly two-thirds could reach the most severe tier. Portsmouth, already Britain's most heat-exposed city, will hold that distinction through 210
Portsmouth faces extreme heat crisis as British cities become urban heat islands
Extreme heat threatens public health and wellbeing, with particular impact on deprived areas with limited green space and cooling infrastructure.
Cities can be up to 10 degrees hotter than surrounding areas
Mark
So Portsmouth is the worst off right now and will stay that way through 2100? That seems almost predetermined.
Mimi
It's not predetermined—it's a trajectory based on current conditions and climate projections. Portsmouth has the structural vulnerability today: lots of hard surfaces, limited green space. Without intervention, that stays the same.
Luke
But the research is projecting 75 years out. How confident are we in those 2100 predictions? Are those based on specific emissions scenarios?
Mimi
The index combines observed temperatures, built-environment characteristics, and climate projections. The Met Office provides the climate data, so it's grounded in their modeling.
Luke
Right, but which scenario? RCP 4.5, 8.5? That matters enormously for the end-of-century picture.
Mark
Let's step back. Why does Leicester jump from 10th to 4th? What's changing there?
Mimi
Leicester is warming faster than most cities because of its built environment and the climate projections for the Midlands. It's not that the city is getting worse—it's that warming accelerates there.
Luke
Or it could be that Leicester's current ranking is lower because it's cooler now, so the same absolute temperature rise looks like a bigger relative jump. The methodology matters.
Mark
The deprivation overlap is striking. Poor neighborhoods have less green space and more heat exposure.
Mimi
Yes. And they have fewer resources to adapt—less air conditioning, less ability to relocate, less political power to demand cooling infrastructure.
Luke
That's true, but the research doesn't quantify that. It maps heat vulnerability, not adaptive capacity. A wealthy neighborhood with high heat vulnerability might adapt more easily than a poor one with lower vulnerability.
Mark
So what actually changes if a city acts? Can Portsmouth do anything?
Mimi
Absolutely. Milton Keynes shows it's possible—more green space, more water features, better urban design. But it requires planning, investment, and political will.
Luke
And time. You can't plant a mature tree overnight. The cities that act now might see results by 2040. Those that wait will be playing catch-up in a much hotter world.
O Pulso
- All 71 of Britain's chartered cities are on course to reach high heat vulnerability by 2040 — not a distant possibility, but a near-certain trajectory already locked in by existing urban form and emissions.
- Urban heat islands trap solar energy in concrete and asphalt, pushing city temperatures up to 10°C above surrounding countryside and turning entire neighbourhoods into slow-release radiators through the night.
- The burden falls unevenly: deprived areas with the least green space and the most hard surfaces will suffer the most intense heat stress, compounding existing inequalities with a physical, thermal dimension.
- London's 2022 heatwaves alone cost the capital £1.5 billion in productivity losses, health impacts, transport disruption, and emergency service strain — a preview of recurring costs if cities do not adapt.
- Milton Keynes offers a counter-model, ranking 69th of 71 for vulnerability thanks to 46 square kilometres of natural surfaces, demonstrating that green infrastructure is not decoration but functional climate defence.
- Planners now have street-level data to locate heat refuges and pre-position emergency responses — the open question is whether Britain's most exposed cities will act on that knowledge before the next heatwave arrives.
As global temperatures rise, Britain's cities are being forced to reckon with a future shaped not just by distant climate projections, but by the concrete and asphalt beneath their own feet. New research from Ordnance Survey, the Met Office, and 4 Earth Intelligence has mapped heat vulnerability across all 71 chartered cities in England, Scotland, and Wales, revealing that by 2040 every one of them will reach high vulnerability — and by century's end, nearly two-thirds could reach the most severe tier. Portsmouth, already Britain's most heat-exposed city, will hold that distinction through 2100, while the pattern of risk falls hardest on the poorest neighbourhoods, where green space is scarcest and the ground holds the most heat. The study is both a warning and an invitation: the knowledge of what is coming now exists, and the question is whether cities will use it.
Portsmouth, a coastal city of 208,000 on England's south coast, is already Britain's most heat-vulnerable place — and new research confirms it will remain so through the end of this century. The analysis, produced by Ordnance Survey, the Met Office, and 4 Earth Intelligence, built a heat vulnerability index for all 71 chartered cities across England, Scotland, and Wales, mapping both current conditions and future trajectories as global heating intensifies.
The mechanism driving the crisis is well understood but relentless. Hard surfaces — concrete, asphalt, buildings — absorb solar radiation by day and radiate it back at night, preventing cities from cooling. The gap between urban and rural temperatures can reach 10°C. Cities with the least tree cover, green space, and waterways are the most exposed, and the research shows the situation will worsen considerably: by 2040, all 71 cities will reach high vulnerability; by 2100, nearly two-thirds could reach the most severe level. Leicester will climb from 10th place today to fourth by century's end, while Exeter, Nottingham, Bristol, and Brighton and Hove will also enter the ten most vulnerable cities. The City of London, dense with buildings and roads and almost devoid of green space, records the highest built-environment score in the study.
Vulnerability is not evenly spread within cities either. In Portsmouth, neighbourhoods like Somerstown, Portsea, and Fratton — areas of economic deprivation with limited vegetation and abundant hard surfaces — face the most intense exposure. The pattern repeats across Britain: the poorest communities, built with less green infrastructure, will bear the greatest heat stress. The costs are already visible; London's 2022 heatwaves alone cost the capital £1.5 billion, covering health impacts, productivity losses, transport disruption, and emergency service strain.
Not every city faces the same fate. Milton Keynes ranks 69th of 71 for heat vulnerability, with 46 square kilometres of natural surfaces moderating its climate far more effectively than most. The contrast illustrates what deliberate green infrastructure can achieve. Researchers describe the index as a tool for turning thermal threats into actionable blueprints — identifying where heat refuges should be placed and how emergency responses can be planned in advance. The data now exists. Whether Britain's most vulnerable cities will act on it before the heat arrives remains the defining question.
Portsmouth, a coastal city of 208,000 people on England's south coast, is already the most heat-vulnerable place in Britain—and new research suggests it will remain so through the end of this century. That finding comes from an analysis by Ordnance Survey, the Met Office, and 4 Earth Intelligence, which has created a heat vulnerability index for all 71 chartered cities across England, Scotland, and Wales. The work maps not just current temperature patterns but how cities will warm as global heating intensifies, revealing which places are most exposed and which have the best chance of adapting.
The mechanism is straightforward but relentless. Concrete, asphalt, buildings, and other hard surfaces in cities absorb solar radiation during daylight hours and then radiate that heat back into the air at night, functioning like enormous radiators that prevent cooling. Rural areas, by contrast, shed heat more readily. The difference is stark: cities can be up to 10 degrees Celsius warmer than their surrounding countryside. The cities most at risk are those with the least tree cover, green space, and waterways—the natural features that would otherwise provide cooling relief.
The research paints a sobering picture of Britain's urban future. By 2040, all 71 cities analyzed will reach high heat vulnerability. By 2100, nearly two-thirds could reach the most severe level. Portsmouth will remain at the highest vulnerability tier throughout. Leicester will climb most dramatically, rising from 10th place today to fourth by century's end. Exeter, Nottingham, Bristol, and Brighton and Hove will also enter the ten most vulnerable cities. The City of London records the highest built-environment score and the least effective natural cooling of any city in the study, given its concentration of buildings and roads and minimal green space. Westminster ranks third for heat vulnerability today and second in both future periods, behind only Portsmouth.
Within cities, vulnerability is not evenly distributed. In Portsmouth, planners have identified Somerstown, Portsea, Southsea, and Fratton as particularly exposed because of their limited green areas and hard surfaces. These neighborhoods overlap significantly with areas of economic deprivation—a pattern that repeats across Britain. The poorest neighborhoods, often built with less vegetation and more concrete, will face the most intense heat stress. Jonathan Hendry, chief executive of 4 Earth Intelligence, noted that exposure varies street by street within a single city, with areas consistently subjected to higher temperatures being the first to overheat during a heatwave.
The economic and social costs are already measurable. A study commissioned by London's mayor calculated that the 2022 heatwaves alone cost the capital £1.5 billion, accounting for productivity losses, health impacts, education disruption, increased energy demand, transport disruption, and strain on emergency services. Nick Bolton, chief executive of Ordnance Survey, emphasized that extreme and sustained heat affects people's health and wellbeing, the comfort of homes and workplaces, and puts additional pressure on transport, energy, and emergency services. Understanding vulnerability requires accurate data about how the country is built—information that planners, developers, and local authorities need now to prepare for a warmer future.
Not all cities face equal peril. Milton Keynes ranks 69th out of 71 for heat vulnerability today, coping far better than most. The city has the lowest built-environment vulnerability in England and the most effective natural cooling of any city in the analysis, with 46 square kilometers of natural surfaces against almost 40 square kilometers of hard surfaces. The contrast illustrates what is possible: cities with sufficient green infrastructure can moderate their own heat. Hendry described the work as mapping how to turn thermal threats into actionable blueprints for urban resilience, supporting decisions on where heat refuges should be located and how emergency responses can be planned in advance rather than improvised during climate events. The question now is whether Britain's most vulnerable cities will act on that knowledge before the heat arrives.
Citações Notáveis
Extreme and sustained heat can affect people's health and wellbeing, how comfortable our homes and workplaces are, and put additional pressure on transport, energy and emergency services.— Nick Bolton, chief executive of Ordnance Survey
The areas consistently subjected to higher temperatures than their surroundings are the ones that overheat first during a heatwave. We're mapping how to turn thermal threats into actionable blueprints for urban resilience.— Jonathan Hendry, chief executive of 4 Earth Intelligence
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