KELLY MCEVERS, HOST:
At the end of every year, meteorologists look back at what the weather was like. And what they saw happen in the U.S. in 2015 was just weird. It was hot, and there were all kinds of extreme weather events. And as NPR's Christopher Joyce reports, all that heavy weather was getting extensive.
CHRISTOPHER JOYCE, BYLINE: December was a fitting end to a strange weather here.
JAKE CROUCH: This is the first time in our 121-year period of record that a month has been both the wettest and the warmest month on record.
JOYCE: Jake Crouch is a meteorologist at the National Oceanic and Atmospheric Administration. He says the rest of the year was very wet and hot, too, the second-hottest on record. The cause - a warming climate and a super-strong El Nino. El Nino is a weather phenomenon out of the Pacific Ocean that hits every few years and affects weather globally. Together, climate and El Nino pushed the average temperature in the U.S. up over its 20th-century average by 2.4 degrees. NOAA scientist Deke Arndt puts that in perspective.
DEKE ARNDT: And if we all went home and reset our thermostat to 2.4 degrees higher in our homes for a year, we would certainly feel the difference.
JOYCE: And when the atmosphere is warmer, it holds more moisture, leading to record snows in the Northeast last February and March and record rain in the South and Midwest. Arndt says scientists expect more of the same.
ARNDT: The fact is we live in a warming world, and a warming world is bringing more big heat events and more big rain events to the United States.
JOYCE: All this weather led to 10 extreme events that each did at least $1 billion in damage. These include a drought, flooding, severe rainstorms, big wildfires and winter storms - a wider variety of costly weather events than usual. Insurance companies are paying for most of this damage. Surprisingly, payouts this year were lower than the previous few years. That, says Mark Bove, is due mostly to luck. Bove is a meteorologist at Munich Re, which insures insurance companies for their losses. He says no serious hurricanes hit the U.S. this year, but he says that's not likely to last. Moreover, he's noticing a trend that's been going on for years and likely will continue.
MARK BOVE: We seem to be seeing more extreme precipitation events. When it rains today, it seems to rain harder and heavier.
JOYCE: But even as the rain gets harder, Bove says people don't seem to be taking notice.
BOVE: We tend to not build buildings to withstand the storms that we already see, let alone how they might change in the future.
JOYCE: And that will mean higher costs in a future where weather appears to be more unpredictable than ever. Christopher Joyce, NPR News.
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