As the sun beat down on the park where he was walking his dog, Gary Youssef described his strategy for keeping cool after days of — comparatively — sizzling London weather. He keeps his windows shut and curtains drawn, and, at night, he opens the windows to let the cool air in. But he is already thinking ahead to next year: Mr. Youssef has been seriously looking into fitting his home with air-conditioning, a relative rarity in Britain. If temperatures continue to rise, he may be keeping a lot cooler by next summer. “A lot more of my friends now have air-conditioning,” Mr. Youssef said.
