A thrill goes down Lane 12, C Block, Kamalpur every time another working-class family brings home its first air-conditioner. Switched on for a few hours, usually to cool a room where the whole family sleeps, it transforms life in this suffocating concrete labyrinth where the heat reached 117 degrees in May . “You wake up totally fresh,” exulted Kaushilya Devi, a housewife, whose husband bought a unit in May. “I wouldn’t say we are middle class,” she said. “But we are closer.” But 3,700 miles away, in Kigali, Rwanda, negotiators from more than 170 countries gathered this week to complete an accord that would phase out the use of heat-trapping hydrofluorocarbons, or HFCs, worldwide, and with them the cheapest air-conditioners that are just coming within reach of people like Ms. Devi. Millions of Indians might mark the transition from poverty with the purchase of their first air-conditioner, […]