PHOENIX — Several million heat-tolerant Arizonans spent the weekend in air-conditioned semi-darkness as temperatures soared to nearly 120 degrees. …Monday will likely bring the 18th consecutive day of temperatures exceeding 110 degrees Fahrenheit in the Valley of the Sun, and the 34th consecutive day of at least 100 degrees. The unrelenting hot weather stems from a stubborn heat dome trapping more than 110 million Americans across the bottom third of the country. …The heat wave comes amid an unusual string of wildfires, floods and other climate disasters around the world, from forest fires in Canada to record flooding in India. …Experts say the primary climate signature of recent heat waves is not daily high temperatures, which can be mitigated through disaster planning and harnessing relief resources. What makes events like this one different is durability. Going forward, extreme heat events in the desert Southwest will no longer be measured in days, but in weeks and even months.