Earlier this year, a group of European researchers published a study with a scorching conclusion: As climate change makes heat waves more prevalent across the continent, the city most vulnerable to excess heat deaths is not a warm southern metropolis, but the relatively cool city of Paris.

Why? In part, the reason is that historically hotter cities have developed adaptations for dealing with extreme heat, from the shady architecture of Palermo to the siestas of Madrid. That leaves Paris at the bottom of a deadly learning curve.

This is just one urgent example of why cities need to talk. The world has an incredible stockpile of effective urban policies, but the best ideas are not being adopted quickly or widely enough. Covid-19 taught us all how to slow the spread of viruses: wear masks, avoid large gatherings and take vaccines. To speed the spread of good ideas, we need to take the opposite tack by making urban solutions go viral.

Reprinted courtesy of Carlo Ratti, Bloomberg and Michael Baick, Bloomberg