Europe's record-breaking heat is changing old habits. Air conditioning, long dismissed as an unnecessary luxury, is becoming a necessity as temperatures cross 38°C and heat-related deaths run into the thousands. Sales are rising fast, with industry association Eurovent projecting that the EU will have over 100 million household ACs by 2030. Here’s the paradox. Together, those machines could emit 15-20 million tonnes of CO2 annually and, unless powered by clean electricity, add to the emissions warming the planet. The heat creates a need for cooling, and the cooling risks adding to the heat. But once societies become used to air-conditioned comfort, will they ever be willing—or even able—to give it up?