The North Pole has been frozen for 100,000 years. But according to scientists, that won't be true by the end of this century. The top of the world is melting. [Pictures of Greenland showed that the ice there has receded dramatically over the last several decades. ] There's been a debate burning for years on the causes of global warming. But the scientists you're about to meet say the debate is over. New evidence shows man is contributing to the warming of the planet, pumping out greenhouse gases that trap solar heat.

Much of this new data was compiled by American scientist Bob Corell, who led a study called the "Arctic Climate Impact Assessment." It's an awkward name — but consider the findings: the seas are rising, hurricanes will be more powerful, like Katrina, and polar bears may be headed toward extinction....

There's long been a debate about how much of this is earth's naturally changing climate and how much is man's doing. Paul Mayewski, at the University of Maine, says the answer to that question is frozen inside an ice core from Greenland.

With funding from the National Science Foundation, Mayewski has led 35 expeditions collecting deep ice cores from glaciers. The ice captures everything in the air, laying down a record covering half a million years.

"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.