Christopher Joyce

Before it got cold this winter, it was warm. Very warm. In fact, new data out Monday shows 2017 was the third warmest year recorded in the lower 48 states.

And it was also a smackdown year for weather disasters: 16 weather events each broke the billion-dollar barrier.

First, the heat. Last year was 2.6 degrees F warmer than the average year during the 20th century.

After Hurricane Harvey, some Texas residents, politicians and scientists are wondering whether the whole U.S. system for predicting floods is any good.

The storm's deluge flooded parts of southeast Texas that had rarely, or never, been underwater before. Some areas got more than 50 inches of rain in a few days. "When the numbers started coming in it was a little scary," says Matt Zeve, the director of operations for the Harris County Flood Control District, which includes Houston.

Hurricane Harvey was the worst flood in Houston's history. Scientists and citizens are still piecing together why it was so bad, but it's becoming clear that a lot of the damage comes down to how people have built America's fourth-largest city.

You can see the problem from your car. Houston is a sprawling web of strip malls and 10-lane freeways.

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Sea levels are rising and climate scientists blame global warming. They predict that higher seas will cause more coastal flooding through this century and beyond, even in places that have normally been high and dry.

But mapping where future floods will strike has barely begun.

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A single tornado can cause a lot of damage. But even worse are tornado outbreaks. Just this week, a cluster of at least 18 tornadoes struck the Southeast over two days.

Scientists are seeing bigger clusters in recent years, and they're struggling to figure out what's happening.

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When scientists tallied the temperature readings from around the world last month, this is what they discovered:

"July, 2016 was the warmest month we have observed in our period of record that dates back to 1880," says Jake Crouch, a climate scientist at the National Oceanic and Atmospheric Administration.

And July wasn't a freak occurrence, he notes. The past 10 years have seen numerous high temperature records.

Buried below the ice sheet that covers most of Greenland, there's an abandoned U.S. Army base. Camp Century had trucks, tunnels, even a nuclear reactor. Advertised as a research station, it was also a test site for deploying nuclear missiles.

If you think it's been hot this year, you're right. The latest temperature numbers from NASA and the National Oceanic and Atmospheric Administration say the first six months of 2016 were the hottest on record around the planet.

You might expect the middle of the Pacific Ocean to be a pretty quiet place, especially a thousand feet down. But it turns out that huge parts of the ocean are humming.

Scientists have puzzled over the source of the sound for several years. Now, a marine biologist reporting Monday at a meeting of ocean scientists in New Orleans says she thinks her team may have figured it out.

If you've ever seen what a Neanderthal is supposed to have looked like, it might be hard to imagine mating with one. But modern humans did. We know because, a few years ago, scientists found stretches of Neanderthal DNA in living humans.

And now there's evidence, from a study published Thursday in Science, that some of that DNA might help shape our health.

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