It was the middle of July and already this summer had become a top contender for the hottest in Texas’s recorded history. In San Antonio, which by July would normally experience about three days of triple-digit heat, there had been three dozen. Houston, Waco and Austin were also seeing temperatures 5 to 8 degrees above normal. The state was roasting and Texans were using a record amount of electricity to stay cool.

New calculations suggest that, by the middle of this century, this record-breaking summer in Texas may look normal.

Across much of the United States, millions of people are expected to experience extreme temperatures more frequently and for longer periods of time — a threat that will grow as climate change worsens.