When the mercury climbs to dangerous levels, it does not discriminate between historic European boulevards and sun-baked Arizona suburbs. This summer, the mayors of Paris, Milan and Phoenix found themselves asking the same urgent question: how do you shield millions of residents when killer heatwaves are no longer freak occurrences but a recurring feature of urban life?
Emmanuel Grégoire, Giuseppe Sala and Kate Gallego came together during London Climate Action Week, held in the grip of a UK heatwave that forced the suspension and cancellation of several scheduled discussions. Across Europe, the human cost has been staggering. More than 14,000 people died during heatwaves this summer, according to the three mayors. The conversation they have begun is not theoretical. It is a matter of survival.
Phoenix Leads the Way in the Desert
For Phoenix, the challenge has shaped municipal policy for decades. The city established one of the world’s first dedicated heat response offices, with a twin mandate: deliver immediate relief to those most at risk while building long-term resilience through structural cooling solutions.
The results have been measurable. New developments in pedestrian-heavy areas must now achieve 75% shade coverage. Cool surface treatments have been applied to more than 300 kilometres of neighbourhood streets, helping to blunt the heat island effect that turns urban landscapes into concrete ovens. Landlords are legally required to keep indoor temperatures at or below 28C (82F), and contractors working with the city must implement heat safety plans for their workers.
The city runs a 24-hour cooling centre offering wraparound services, ranging from medical care to housing support and even job placement. During the summer of 2024, the hottest on record in Phoenix, these coordinated measures contributed to a 20% year-over-year decline in heat-related 911 calls. Lives saved, not merely statistics.
European Capitals Rewrite the Rules of Urban Living
Paris and Milan face a different inheritance. Their streets, squares and stone buildings were designed for a climate that no longer exists.
Paris has responded with ambition. Every resident now lives within a seven-minute walk of one of more than 1,400 designated cool spots, comprising parks, gardens and public facilities where people can take shelter during heatwaves. Opening hours for parks, swimming pools and public baths are extended when temperatures spike. A network of 27,000 climate volunteers is mobilised to spread awareness of heat risks and adaptation strategies across neighbourhoods.
The city is also rehearsing for the unthinkable. In October 2023, Paris staged an exercise called “Paris at 50°C,” testing municipal responsiveness under simulated catastrophic heat conditions. Schools, utilities, media and community groups all took part. Barcelona has since announced it will run the same drill in 2027.
Milan, drawing inspiration from both Paris and Barcelona, is weaving cooling into its broader urban design. The city’s Piazze Aperte (Open Squares) and School Streets programmes are being expanded with tree planting, permeable green surfaces and new shaded areas. Through Milano Aiuta (Milano Helps), elderly and vulnerable residents can access dedicated helplines and support services. The city’s Air and Climate Plan sets a legally binding target to limit local temperature increases to 2C by 2050, one of the only such temperature-related commitments in the world.
A Global Crisis Demands Global Solutions
Geography, history and politics may differ from city to city, but the lessons travel well. Through the C40 Cities network, nearly 100 of the world’s largest urban centres are now exchanging climate solutions, ranging from cooling public spaces to protecting outdoor workers to communicating risk effectively.
Extreme heat is already the deadliest climate hazard on the planet, claiming more than 500,000 lives annually. Cities are particularly exposed because buildings, roads and pavements absorb heat throughout the day and release it long after sunset, denying residents the respite their bodies need. Older people, young children, outdoor workers and lower-income communities consistently bear the heaviest burden.
The three mayors argue that the solutions cannot be left to the most vulnerable alone. National governments must work with cities to strengthen adaptation strategies, expand early warning systems and unlock the finance local leaders need to protect their residents. The cost of inaction is measured in lives, and it is paid first by those with the least.
The Political Imperative of Cooling
Heating and cooling account for nearly half of all energy consumption in Europe, with roughly 70% of heating still generated by fossil fuels. Cities, the mayors argue, have the power to lead a fair transition to clean heat, cutting emissions, improving air quality and creating local jobs in the process.
This summer offered Europe a preview of conditions that residents of desert cities endure routinely. That future, the mayors warn, is fast becoming the norm for everyone. Heat is not a private inconvenience to be endured behind closed curtains. It is a political crisis that demands bold, coordinated action.
The climate emergency is rewriting what counts as normal at breathtaking speed. The capacity of cities to learn from one another, they insist, must move faster still.
Why it Matters
The message from Paris, Milan and Phoenix cuts to the heart of how the world must confront a heating planet. Extreme heat is no longer a distant threat confined to equatorial regions or desert climates; it is a lived reality for millions across every continent, and it is intensifying. When the mayors of three vastly different cities agree on the urgency of the moment, policymakers and residents alike should take notice. Treating heat resilience as a luxury, or as someone else’s problem, is no longer tenable. The investments cities make now, from tree cover to cool roofs, from worker protections to early warning systems, will determine whether future summers bring inconvenience or mass casualty. The window for bold action is narrowing with every passing heatwave.
