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This summer, mayors met in London during the heatwave that ironically threatened to derail London Climate Action Week.
As temperatures broke records across the UK and Europe, leading some climate talks to be suspended or cancelled, we found ourselves seeking shelter and comparing how our cities prepare for extreme heat: how we protect vulnerable residents, communicate risk, and redesign neighbourhoods for hotter summers.
At the same time, Paris was overseeing the city’s crisis response as another intense heatwave swept across France. Across Europe, more than 14,000 people lost their lives due to the heat.
As mayors, we are confronting the same question: how do you protect millions of people when extreme heat is no longer an exceptional event, but an increasingly familiar part of summer?
For Phoenix, that question has shaped city government for decades. For Paris and Milan, it is now becoming one of the defining challenges of urban leadership.
It may strike some people as unusual that two of Europe’s oldest and most prestigious cities are looking to a city in the Arizona desert for ideas. But rising temperatures are now a global challenge, and we don’t have time for each city to figure out what works on its own.
Phoenix has learned, sometimes the hard way, that extreme heat cannot be treated as simply a weather event. It shapes decisions about transport, housing, public health, public space, and emergency planning. Preparing for summer begins long before temperatures start to rise.
Phoenix established one of the world’s first city offices dedicated to heat response and mitigation, reflecting an approach that focuses on both immediate relief from extreme heat, especially for those most vulnerable, and building resilience in the medium-long-term by implementing cooling solutions to make the city safer and more comfortable.
The city’s shade plans require 75% shade coverage in new development in areas with high pedestrian activity, and programs that support schools, transit users, and those most vulnerable. To further reduce the urban heat island effect, Phoenix is applying cool surface treatment to buildings and roadways, including on more than 300 kilometers of neighborhood streets.
The city leads its region in heat response, including providing a 24-hour cooling center with wraparound support to connect people with resources such as housing, medical services, and even job placement. Landlords are required by law to maintain a safe indoor temperature (28C/82F or lower), and companies that contract with the city must implement heat safety plans to keep workers healthy and comfortable. These measures save lives: during the summer of 2024, which was the hottest on record in Phoenix, the city’s coordinated heat response measures contributed to a 20% year-over-year decline in heat-related 911 calls.
Paris and Milan bring different expertise as well as unique challenges.
Both are historic European cities where streets, buildings and public spaces were designed for a different time and a different climate. Today, both cities are adapting.
Every Parisian now lives within a seven-minute walk of a cool spot. The city now has more than 1,400 of these spaces where people can cool down during a heatwave, including parks, gardens and other public facilities. The city also extends opening hours for parks, swimming pools, and public baths during high temperatures. The city has mobilised a network of 27,000 climate volunteers to raise awareness within their communities of the climate crisis and heatwave adaptation strategies, alongside preventive actions.
The city is also planning for a future that would have been inconceivable to Parisians just a few decades ago: “Paris at 50°C” was organised in October 2023 to test the responsiveness of the municipality and its partners, as well as improve planning and coordination for future heat emergency responses. This involved the whole community, utilities, media and schools and directly inspired Barcelona to carry out the same exercise in 2027.
No city can simply import another’s model. Geography, history and politics are different everywhere. But every mayor owes it to their residents to gather the best ideas from cities around the world; and through the C40 Cities network, nearly 100 of the world’s biggest cities are sharing climate solutions for our residents and businesses. Cities have always learned from one another. We have adapted successful transport systems, housing policies and public health measures for generations. Heat adaptation should be no different.
If one city discovers a better way to protect outdoor workers, cool public spaces or communicate risk to residents, others should not spend years reinventing it. Good ideas should travel.
Inspired by Barcelona and Paris cool spaces initiatives, Milan is expanding its Piazze Aperte (Open Squares) and School Streets programme to integrate cool spaces by planting trees, replacing hard surfaces with permeable green space and creating shaded areas. The Municipality also provides a helpline and support services for the elderly and vulnerable residents through Milano Aiuta (Milano Helps). Milan’s Air and Climate Plan outlines a binding goal to limit local temperature increases to 2C by 2050; they are one of the only cities in the world that has set a temperature-related target, which is very ambitious.
Extreme heat already claims more than half a million lives every year, making it the deadliest climate hazard. Cities are particularly exposed because buildings, roads and pavements absorb heat during the day and release it long into the night, meaning residents get no respite and struggle to cool down properly. Older residents, young children, outdoor workers and lower-income communities often face the greatest risks.
Planting trees, cooling schools, redesigning streets, improving buildings, and expanding early warning systems are often described as climate policies. They are also public health measures, investments in local economies, and practical improvements that make cities more liveable throughout the year.
Meanwhile, heating and cooling account for nearly half of all energy use in Europe, with about 70% of heating still generated by fossil fuels. Cities have the power to lead a fair transition to clean heat. By investing in renewable energy and cleaner heating systems, they can cut emissions, improve air quality, and create local jobs, ensuring the benefits reach those who need it most.
Cities are often the first to experience climate impacts but the last to receive the powers, funding and flexibility needed to respond. National governments should work with cities to develop more effective adaptation strategies, expand early warning systems, and make it easier for local leaders to access the finance needed to protect residents. Those investments can save lives, strengthen economies and reduce future costs across the entire country.
This summer has given Europe a glimpse of what those living in desert climates feel so often, and what we can all expect to become our norm in the age of climate crisis.
Extreme heat is not an individual burden; it is an existential challenge we must all rise to. The responsibility cannot fall on the shoulders of an isolated pensioner, a vulnerable child or a construction worker. Heat is a political crisis that demands bold political action.
We must prepare and fight back. The climate crisis is redefining what our definition of “normal” is at a rapid rate. Our ability to learn from one another must move even faster.
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Emmanuel Grégoire, Giuseppe Sala and Kate Gallego are the mayors of Paris, Milan and Phoenix
