In Death Valley, California, the temperature reached 128° Fahrenheit (53° Celsius) on Sunday—just 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 wave? Is global warming a factor? And how does it compare with past events? We talked to Martin Tingley, a climatologist at Harvard University, to find out.

In April, Tingley and his colleague Peter Huybers published a study in the journal Nature that concluded that the years 2005, 2007, 2010 and 2011 were warmer than any year going back 600 years, to 1400.

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