Last July, Antalya on the Turkish Riviera broke records when temperatures crept above a scorching 46°C. Home to more than 2.6 million people – and millions more tourists each summer – the Mediterranean city was long accustomed to heat.
But something had shifted.
“In recent years the heat has changed in character: heatwaves that are longer, more intense and more frequent, straining our residents, our outdoor workers, our health services and the millions of visitors we host each year,” says Melike Kireçcibaşı, Head of Antalya’s Climate Change and Zero Waste Department.
Antalya is not alone. Extreme heat is now the deadliest climate hazard on Earth, killing nearly half a million people every year.
Europe’s May heatwave – which saw temperatures in France run 10 to 15 degrees above normal, breaking all-time spring records and causing deaths across the continent – was described by UN climate chief Simon Stiell as a “brutal reminder of the spiralling impacts of the climate crisis”.
With the World Meteorological Organization (WMO) warning that a potentially powerful El Niño is now developing, set to amplify already-rising temperatures across Europe and beyond this summer, the pressure on cities to act has never been greater.
Now, on World Environment Day (5 June), more than 50 mayors – from Athens to Oulu to Yangzhou – are joining forces. The United Nations Environment Programme’s new ‘50@50’ initiative brings cities together to share tested solutions, stress-test their systems against future heat scenarios, and accelerate action before the next heatwave strikes.
“Extreme heat is already reshaping daily life in cities around the world,” says Inger Andersen, UNEP’s Executive Director. “50@50 helps local leaders move faster by sharing practical solutions that protect people, reduce inequality and strengthen urban resilience.”
Mapping heat exposure for targeted action
Prompted by rising temperatures, Antalya embarked on the EU-supported CLIMAAX-MUHIR project – a province-wide heat-risk assessment modelling current and future dangers.
“The findings were sobering,” Kireçcibaşı tells Euronews Earth. “Our climate projections show heatwave occurrence rising sharply under a high-emissions scenario; some districts could see several-fold increases in heatwave frequency by mid-to-late century.”
The project also mapped where vulnerable populations and extreme heat intersect – and the results were stark. Although built-up areas make up just 2.56 per cent of Antalya’s territory, they house around 56 per cent of its population, and the city’s highest-risk heat zones overlap almost precisely with where people actually live. “That tells us where to act first,” says Kireçcibaşı.
Guided by these findings, Antalya developed a Heat Action Plan directing cooling infrastructure, shade, green spaces, early-warning systems and health support to the neighbourhoods that need them most.
Redeveloping the most vulnerable neighbourhoods
A similar approach is underway in Athens – another 50@50 participant – where an Urban Heat Atlas identifies where heat exposure and social vulnerability overlap. The initiative is driving the redevelopment of Elaionas, one of the city’s most thermally vulnerable districts, where a new 215,000-square-metre metropolitan park is being created.
Athens has committed to planting 5,000 trees every year; since 2024, more than 12,400 have already gone into the ground. Progress can be tracked in real time through the Athens Trees digital platform, designed to build public trust and citizen engagement.
“Combined with school gardens, microforests, neighbourhood parks and cooling elements in public spaces, these interventions are helping us create a cooler and healthier urban environment,” says Elissaios Sarmas, CEO of Develop Athens.
Both cities hope their hotspot-mapping techniques will be among the most transferable contributions to the 50@50 network.
That sharing of knowledge is the initiative’s core purpose. Building on its own 50°C simulation exercise – in which the city stress-tested its systems against temperatures it has not yet experienced but scientists say it will – Paris is now helping to extend that model across the network.
“Extreme heat is becoming a defining challenge for cities worldwide,” says Emmanuel Grégoire, Mayor of Paris. “Cities must act together to anticipate extreme heat and protect their residents. Cooperation is our most powerful tool.”
Over the next year, a dozen cities will conduct their own extreme heat stress tests with support from UNEP, the C40 Cities Climate Leadership Group and the City of Paris.
Heat is hitting from the Mediterranean to the Arctic Circle
Perhaps the most striking signal of how far the extreme heat problem has travelled comes from a city near the top of the world. Oulu, the EU’s northernmost large city in Finland, sits close to the Arctic Circle – and yet it too has joined 50@50.
Last year, Finland endured three consecutive weeks of 30°C temperatures in a “truly unprecedented” heatwave. An ice rink in the north of the country opened up to those seeking refuge from the heat, while local hospitals were inundated. The heatwave also sparked concerns over the welfare of reindeer, who risked overheating.
“The urban heat islands are starting to form and make urban spaces uncomfortable,” says City Architect Sanna Pääkkönen. The challenge is compounded by the fact that the Finnish city was built for an entirely different climate.
“Most of our apartments, schools, daycare centres and working environments are built with cold winters in mind – and now they are getting too hot in summer,” Pääkkönen explains.
Beyond heat, Oulu’s Climate Roadmap must also contend with more frequent flooding, storms, and the disruption that shifting freeze-thaw cycles bring to buildings and infrastructure designed for reliable permafrost.
City planners are now factoring sunlight, heat and shading into new urban developments – and investing in cycling and pedestrian infrastructure to cut the car emissions that drive the temperatures they are scrambling to adapt to.
The thread connecting Antalya’s heat maps, Athens’ new parks and Oulu’s rewritten planning rules is the same: cities can no longer design for the climate they have. They must design for the one that is coming.
That a city near the Arctic Circle is now planning for summer heat it was never built to handle demonstrates how rapidly the problem is moving. Keeping pace with it, 50@50’s organisers argue, requires cities to stop trying to solve it alone.
