National Geographic: The American Southwest is broiling in triple-digit temperatures for the fourth consecutive day as a result of a record-breaking heat wave that is smothering the region.
In Death Valley, California, the temperature reached 128° Fahrenheit (53° Celsius) on Sundayjust a few degrees shy of the July 10, 1913, record of 134° Fahrenheit (57° Celsius).
The heat wave has also been partly blamed for a wildfire that killed 19 firefighters on Sunday in Yarnell Hill, Arizona.
So what's behind the heat...