NEW YORK (AP) — In the opening scene of American writer Kim Stanley Robinson's "The Ministry for the Future," a heat wave combined with a breakdown of the electrical grid in India kills 20 million people. The devastation causes the world's nations to unite to combat climate change.

Scientists have long warned that the world will experience more intense extreme weather events like heat waves, storms, floods and droughts. But what once seemed like the realm of fiction is now discussed as a possibility, even an inevitability.

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Warning about an "extreme of extremes" or the "Other Big One," a play off the California reference of a big future earthquake, can be fraught. After all, nobody can say for sure when a weather catastrophe may happen. But in the last few years, the planetary ingredients needed for a massive disturbance have been building. And alarm is growing.

"The risk is that people just think you are exaggerating," said Daniel Swain, a climate scientist with the California Institute for Water Resources. "It's the 'Boy Who Cried Wolf' problem. Sometimes wolves are real. If it's outside the door, wouldn't you want to know?"