Cities concentrate human activity, but they also concentrate risk. When a coastal city floods, millions lose their homes, businesses, and infrastructure in a single event. When a heat island effect amplifies an already-dangerous heat wave, it kills disproportionately among the old and the poor. Climate change doesn't treat everyone equally — and it doesn't treat all cities equally either.

The most vulnerable cities share certain features: low elevation, proximity to water, dense informal settlements, and governments without the resources to adapt. Jakarta is sinking into the Java Sea while flooding from above. Miami sits on porous limestone that seawater rises through from underneath. Phoenix faces summers that may exceed the thermal limits of outdoor human survival.

But some cities are already adapting — and their experiments offer lessons that could scale globally. Rotterdam has redesigned itself around water management. Singapore has invested in shading, green corridors, and cooling strategies as survival infrastructure. Copenhagen has 'cloudburst plans' for the extreme rainfall events that happen once every few decades but now happen every few years.