In the crowded lanes of Mathare, one of Nairobi’s oldest and densest informal settlements, the rising sun no longer brings promise it brings peril. Vendors who once sold fish and fresh produce from their wooden stalls are now fighting against the day’s heat to prevent their goods from spoiling before they find buyers. On the streets of Mathare, where temperatures can soar five degrees Celsius higher than the rest of Nairobi, the heat forces many sellers to pack up early or suffer headaches, exhaustion, and lost earnings.
What’s happening in Mathare is no local anomaly. This scene is now replicated in hundreds of cities across the globe as climate change drives temperatures higher and extreme heat becomes a daily reality rather than a rare disruption. Cities from Los Angeles to Dhaka to Jodhpur are feeling the impact, as the simple act of living, working, or commuting becomes increasingly dangerous. More than 350 cities worldwide are already grappling with summer temperatures exceeding 35°C—a number set to rise dramatically.
Extreme heat is no longer just a health risk. It’s an all-encompassing urban crisis that is reshaping health systems, transportation networks, economic stability, and livelihoods. The toll is heavy and growing.
Health systems on edge
As temperatures soar, urban health risks intensify. Prolonged exposure to extreme heat causes organ strain, disrupts sleep patterns, elevates mental stress, and worsens chronic illnesses such as asthma and heart disease. Vulnerable populations—children, pregnant women, the elderly, and outdoor workers—face the greatest threats. In slums and informal settlements where homes are often built from heat-trapping materials like corrugated metal, the risk is magnified. Without adequate ventilation or cooling, residents endure suffocating conditions day and night.
In response, some cities are trying to protect their people. Buenos Aires and Athens have launched heat early-warning systems. Phoenix, Arizona opened 24/7 cooling centers last year that served thousands of unhoused residents. Meanwhile, Jodhpur’s net-zero cooling shelter fitted with misting fans, solar panels, and passive wind towers offers a rare haven where indoor temperatures stay 12°C cooler than the searing streets outside.
But these measures only scratch the surface. Long-term solutions require data-driven strategies—mapping local heat risks, identifying vulnerable populations, and investing in green infrastructure like tree canopies and reflective “cool roofs” that can reduce home temperatures by as much as 91% annually.
Transportation grinds to a halt
Extreme heat is threatening city mobility systems, discouraging people from using public transit, cycling, or walking. In U.S. cities like Chicago and New York, public transport usage drops by nearly 50% on hot days as riders avoid sweltering stations and unshaded stops. Cyclists abandon bike lanes as temperatures cross 28°C. Yet those who can’t afford cars—often the poorest residents—have no choice but to suffer the heat.
Cities like Medellín, Colombia, are leading the way by redesigning streets into “green corridors”—tree-lined pathways that reduce temperatures, improve air quality, and encourage walking and cycling even in heatwaves. But elsewhere, infrastructure lags behind. Los Angeles, for example, shelters only 25% of its bus stops, leaving most riders exposed.
Jobs and incomes under threat
For millions of urban workers, extreme heat means falling productivity and rising poverty. Construction workers, street vendors, garment factory employees all face mounting risks as heat slows their output and damages their health. In Dhaka, Bangladesh, garment sector income losses from heat are already nearing 10%. In New Delhi’s textile hubs, women labourers pushing heavy carts under the blazing sun suffer the dual burden of economic insecurity and heat stress.
Local governments are beginning to react. California’s Heat Action Plan mandates rest breaks, cooling facilities, and ventilation standards. Freetown, Sierra Leone, is experimenting with UV-resistant canopies for market stalls. But these interventions remain rare exceptions rather than the norm.
The hidden economic cost
Heat is silently draining city economies. In Los Angeles, heat-related productivity losses now top $5 billion annually. In Bangkok, each 1°C rise could cost $500 million in extra energy demands. Infrastructure too is cracking under the strain—roads buckling in Houston, data centers failing in London’s hospitals, causing costly service disruptions.
Experts warn that without bold investment in heat-resilient urban design—cool pavements, green roofing, shaded streets—the price of inaction will far exceed the cost of prevention.
A global call for action
The heat crisis is global, but solutions are still fragmented and underfunded. Cities like Phoenix, Medellín, and Jodhpur offer glimpses of the future—where urban design, technology, and public health work together to create cooler, safer, and more livable environments. Yet for most cities, progress is too slow and too limited.
From Mathare’s struggling street vendors to New York’s bike commuters and Dhaka’s garment workers, the message is clear: Urban heat is no longer a summer inconvenience it’s a system-wide threat to life, work, and prosperity. Unless cities worldwide accelerate efforts to protect their people and redesign their infrastructure, the rising temperatures of tomorrow will cripple the economies, health, and stability of today’s urban world.
The race to build heat-resilient cities has begun—but not every city is running fast enough.