India, July 4 -- Last week, I travelled to Paris and Amsterdam expecting the familiar European summer: long walks, cycling through breezy streets, and evenings that called for a light jacket. Instead, I found myself stepping into a heatwave that felt strangely familiar. As someone from Delhi, I wasn't surprised by the temperature. What surprised me was watching cities built around walking and cycling confront a kind of heat they were never designed for.

And yet, despite the heat, what sustained itself was the active lifestyle. Whether along the Seine in Paris or beside Amsterdam's canals, people continued to run, cycle and walk through temperatures above 35degC. But how long can cultures built around outdoor movement withstand a warming ...