A relentless heat wave that refuses to let up brings danger to California, Southwest

For nearly a month, millions of people across the American Southwest have sizzled, sweated and sweltered under a heat wave that refuses to let up.

Day after day, residents from Fresno to Phoenix have endured triple-digit temperatures and hot, restless nights that have offered little relief.

Forecasters say the heat wave is being driven by a ridge of high pressure that has parked itself over the region, creating a pressure cooker of slowly sinking warm air.

But some experts say it is a worrisome indication of a climate that has been radically altered by human behavior colliding with the onset of El Niño.

"We would not see the kinds of temperatures globally