"We can go to any section of the ice core, to tell, basically, what the greenhouse gas levels were; we can tell whether or not it was stormy, what the temperatures were like," Mayewski explains.

60 Minutes brought Mayewski back to Greenland, where he says his research has proven that the ice and the atmosphere have man's fingerprints all over them.

Mayewski says we haven't seen a temperature rise to this level going back at least 2,000 years, and arguably several thousand years.

As for carbon dioxide (CO2) levels, Mayewski says, "we haven't seen CO2 levels like this in hundreds of thousands of years, if not millions of years."

What does that tell him?

"It all points to something that has changed and something that has impacted the system which wasn't doing it more than 100 years ago. And we know exactly what it is. It's human activity," he says.

It's activity like burning fossil fuels, releasing carbon dioxide and other greenhouse gases. The U.S. is by far the largest polluter. Corell says there's so much greenhouse gas in the air already that more temperature rise is inevitable.

Even if we stopped using every car, truck, and power plant — stopping all greenhouse gas emissions — Mayewski says the planet would continue to warm anyway. "Would continue to warm for another, about another degree," he says.

That's enough to melt the Arctic — and if greenhouse gases continue to increase, the temperature will rise even more. The ice that's melting already is changing the weather by disrupting ocean currents.

Corell points to floods in the U.S., heat waves in Europe; and 60 Minutes wanted to know about the catastrophic 2005 hurricane season.

"The one thing I think we can say with a fairly high degree of confidence is the severity of the storms, how strong the storms, these cyclonic events like hurricanes and cyclones in the Pacific, are going to get — they're gonna be more severe. Now one thing that is in doubt is whether there'll be more of them," Corell explains.

"The oceans of the Northern Hemisphere are the warmest they've been on record. When they get up in that temperature, they spin off hurricanes. Well, if it goes up another degree, it's gonna spawn these with more intensity," Corell says.