Teen and Stepfather Die on Hike in Near-Record Texas Heat

Mr. Gates’s mail route spanned 400 homes and eight miles, said his wife, Carla Gates. On Tuesday morning, he had gotten an early start, as usual, and packed a cooler with ice water. A couple of hours after sunrise, he texted his wife to tell her that it was already 88 degrees outside, she said.

“If you go out, be careful,” he wrote. It was his last message to her.

The early-summer heat has been brutal even in places where residents are used to hot summers. At Main Street Mowing in the northern suburbs of Dallas, business always picks up when temperatures hit the triple digits, said Tanner Maxson, who owns the business. This year, though, the calls are coming in late June, not July or August.

“People are throwing in the towel,” Mr. Maxson said. “The phone has been ringing off the hook.”

Temperatures in the Dallas area were expected to reach 103 on Monday, with a heat index of about 110. By Wednesday, the National Weather Service expects temperatures to reach about 107. Highs in late June are typically in the low 90s.

While tying a single heat wave to climate change requires analysis, scientists have no doubt that heat waves around the world are becoming hotter, more frequent and longer lasting. The 2018 National Climate Assessment, a major scientific report by 13 federal agencies, noted that the frequency of heat waves in the United States jumped from an average of two per year in the 1960s to six per year by the 2010s.

In Austin, temperatures were also expected to reach about 103 on Monday. “No one can survive this,” said Paula Knight, 34, who runs a small business advisory group and tried — only briefly — to get some work done at an outdoor table at a coffee shop on Monday afternoon.

Still, some residents said they were accustomed to the scorching heat. While walking on Monday morning in north Austin, Petr Obrda, 79, said: “This is summer in Texas.”

David Montgomery contributed reporting from Austin. John Keefe also contributed.