Cities on the Edge: The Heat Is Here; the Choices Are Ours

This past summer's record heat showed that even London is not ready for a warming world. For the fast-growing secondary cities of Africa and Asia, the decisions that will determine who survives the coming decades are being taken right now, argues Loretta Hieber Girardet in a public keynote to University College London re-published in Global Geneva.

OPINION

On 24 June, 2026, I stood before an audience at University College London and asked a simple question: how many of you think London is prepared for a warming planet? Not a single hand went up.

Outside, Britain was living through its first-ever three consecutive days of red extreme-heat warnings. Schools were closing early, Tube lines were breaking down, and a London Climate Action Week event on extreme heat at the London School of Economics had been cancelled. Al because of extreme heat. By the end of that week, the UK had broken its June temperature record three days running, peaking at close to 38°C in Norfolk, more than two degrees above the record set in 1976.

If one of the wealthiest cities on earth struggles to cope, what does this mean for cities in Africa and Asia that have nothing like London's resources?

African and Asian cities must prepare themselves for more intense heat.

Rohan Ready/Unsplash

The data that have emerged since then only sharpen the question. Scientists at Imperial College London, the Met Office and the London School of Hygiene and Tropical Medicine estimate that the May and June heatwaves killed some 2,700 people in England and Wales alone. Climate change added 3–4°C to peak temperatures and accounts for roughly 42 per cent of those deaths.

Across the Channel, France recorded its hottest day ever on 23 June, and Santé Publique France counted more than 2,000 excess deaths in a single week. EuroMOMO, the European mortality monitor, logged over 10,600 excess deaths across 27 countries between 22-28 June. One preliminary estimate, not yet peer reviewed, puts the continent's toll for that week above 20,000.

Heat-attributable deaths have risen in 99.6 per cent of monitored European regions, reaching some 62,000 in 2024,

The 2026 Europe report of the Lancet Countdown 2026

None of this is part of a freak occurrence. The 2026 Europe report of the Lancet Countdown found that heat-attributable deaths have risen in 99.6 per cent of monitored European regions, reaching some 62,000 in 2024, while extreme-heat warnings have more than quadrupled since the 1990s. Worldwide, heat already kills an estimated 546,000 people a year.

And these are almost certainly undercounts. The UN Office for Disaster Risk Reduction (UNDRR) maintains a global system for tracking disaster losses; as of last year, only six countries were classifying extreme heat as a disaster and counting its dead. A heat-induced heart attack is rarely recorded as a heat death; nor are the drownings of people who plunge into lakes and rivers to escape the heat, as dozens did in France this past summer.

Cooling off in rivers and lakes also presents a risk

Tomek Baginski/Unsplash

A paradox of knowledge

Here is the paradox that should trouble us. We have never known more about what reduces disaster risk. In the 1920s, disasters killed an average of 500,000 people a year; today the figure is around 70,000. Yet extreme heat is now bending the mortality curve back upwards, and the economic bill keeps rising.

Reported direct disaster losses more than doubled between 2001 and 2020 to some US$200 billion a year. Count the disrupted schools, hospitals and livelihoods, and the true annual cost nears US$2.3 trillion. Heat alone could cost the global economy around US$2.4 trillion by 2030 and wipe out the equivalent of 80 million full-time jobs.

Cities sit at the sharp end. Concrete, asphalt and missing trees can make cities 8–12°C hotter than the surrounding countryside. New research suggests that the gap is widening. A study published in PNAS (Proceedings of the National Academy of Sciences in the United States), a peer-reviewed multidisciplinary scientific journal, this year found that 81 per cent of 104 medium-sized cities in the tropics and subtropics are projected to warm faster than their rural surroundings even if global warming is held to 2°C, in some cases by 50 to 100 per cent more. Another analysis of 936 cities found urban heatwaves intensifying faster in the Global South than in the North.

The largest urban experiment in history

This matters because we are living through the largest urbanisation experiment in human history. By 2050, some 5.2 billion people (about 70 per cent of humanity) will live in cities, up from 4.4 billion today.

The story is not mainly about metropolises such as Mumbai or Lagos. It is being written in secondary cities of one to five million people, growing at 3-5 per cent a year, where planning cannot keep pace and building codes often exist only on paper. As it is, 1.1 billion people already live in informal settlements, pushed onto floodplains and eroding hillsides at the city's edge, where the floodwaters arrive first and the shade last.

Nor does heat does strike evenly. During Europe's 2003 heatwave, which killed some 70,000 people, mortality in Paris's poorer, high-density arrondissements was up to four times that of wealthier districts. After Chicago's 1995 heatwave killed more than 700 people in five days, researchers found that neighbourhood social cohesion predicted more effectively who died than temperature, age or health.

Heat hazard is only half the story. The rest is vulnerability: who has trees, insulation and savings, and who has a neighbour who knocks on the door. This summer, my own village in France circulated a list of elderly residents and asked the rest of us to check on them. Such precautions costs almost nothing.

London: the need to prepare for greater extreme heat

Photo: Courtesy Heat Ready London

Response is not resilience

Most governments still treat heat as an emergency to be managed when it arrives, such as messages on the Tube about drinking water, school closures, cooling centres. They save lives, but they are response plans, not transformation plans. London published Heat Ready London, its first city-wide heat plan, the day after my talk, a welcome step. The test for London, and for every city, however, is whether such plans go beyond the next heatwave to reshape housing, transport, green space and energy for a climate that has already changed.

Some cities are showing the way. Medellín in Colombia, once a byword for violence, stabilised the slopes where its poorest residents live, linked them to the centre with new transport and threaded green corridors through the city, lowering temperatures by around 2°C. Sierra Leone’s Freetown is replanting urban forests; Semarang in Indonesia is restoring mangroves, while Surat, India and Kampala, Uganda are protecting wetlands.

Nature-based solutions cost a fraction of grey infrastructure. Resilient infrastructure, meanwhile, costs on average just 3 per cent more upfront but can cut repair and maintenance costs by half or more in high-risk locations. An investment of around US$800 million in early warning systems could prevent losses of up to US$16 billion a year.

If cities do not make these choices, markets will make them instead. Insurers are not driven by ideology but by actuarial models. In 2023, major insurers stopped writing new homeowner policies in California, citing wildfire risk; parts of northern Australia are becoming uninsurable. Without insurance there are no mortgages, property markets stagnate and tax bases erode. Cities that fail to act risk falling into a recovery trap, in which every crisis consumes the money needed for development. This is a pattern already visible in parts of Bangladesh, Haiti and the Sahel.

Why we fail to act

Why, then, the inaction? Political cycles last four or five years; resilience pays off over decades. Prevention is invisible: there are no headlines for the disaster that did not happen. Heat cuts across health, education, transport, energy and finance, yet few governments have anyone pulling those ministries together. And above all, the people who bear the greatest risk - informal settlement residents, outdoor workers, the elderly and the poor - are rarely the ones making the decisions. That is not incidental to the risk map. It is what draws it.

Somewhere today, a city official is deciding where the next neighbourhood will be built. Somewhere else, a budget is being approved that will either lock in resilience or lock in risk for decades. Constructing a road is a 30-50-year decision, not a five-year one. As London learned last June, resilience is not a challenge for somebody else's cities. It is a challenge for our own. The future is not something that happens to cities. It is what we build. And we are building it now.

Loretta Hieber-Girardet is Chief of the Risk Knowledge, Monitoring and Capacity Development Branch at the UN Office for Disaster Risk Reduction (UNDRR) in Geneva. This article is adapted from her keynote address, "Cities on the Edge", at the 16th UCL Risk and Disaster Reduction annual conference in London on 24 June 2026. The views expressed are her own. [Watch the full keynote: VIDEO LINK] Full disclosure: Loretta is married to Edward Girardet, editor of Global Geneva.