New Delhi, July 29 -- India became the pharmacy of the world by supplying affordable medicines to more than 200 countries, dominating the global market for generic drugs and producing a large share of the world's vaccines.

This success rests on an assumption so basic that it is rarely discussed.

Indian firms have shown that drug formulations can be made, stored and transported under tightly controlled conditions without fail. But as climate change turns heatwaves, floods and extreme rainfall more frequent, this assumption is becoming harder to sustain.

The risks extend far beyond damaged buildings or delayed deliveries. They strike at the reliability on which India's pharmaceutical industry has built its reputation. It also comes at an...