William Brangham:

That's right, Judy.

Last month was the hottest June on record going back 139 years, according to NASA. And, today, halfway into July, the National Weather Service forecasts potentially deadly temperatures throughout the weekend across much of the United States.

This week, a study by the Union of Concerned Scientists warned that the number of extreme heat days could more than double by mid-century, just 30 years away, if we don't change how much of those heat-trapping gasses we emit.

For more on where we are and where we might be going, I'm joined by Astrid Caldas. She's a senior climate scientist at the Union of Concerned Scientists.

Welcome.