A Global Warning

By: Daniel Schorn

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International Atomic Energy Agency chief Yukiya Amano, left, shakes hands with Iran's chief nuclear negotiator Saeed Jalili in Tehran, Iran, May 21, 2012. (AFP/Getty Images)

Polar bears can only hunt on the ice. Lunn says the ice is breaking up three weeks earlier than it did 30 years go. He's now finding female bears 55 pounds lighter — weaker mothers with fewer cubs.

Asked how the bear population has changed since he started his research, Lunn says, "When we first started doing this research, we've done inventories in the mid-80s, in the mid-90s. Both times we came out with an estimate of approximately 1,200 animals for what is known as the western Hudson Bay population. The numbers now suggest that the population has declined to below 1,000."

The bears are unlikely to survive as a species if there's a complete loss of ice in summer, which the arctic study projects will happen by the end of this century.

There are skeptics who question climate change projections like that, saying they're no more reliable than your local weatherman. But Mayewski says arctic projections done decades ago are proving accurate.

"That said, the skeptics have brought up some very, very interesting issues over the last few years. And they've forced us to think more and more about the data that we collect. We can owe the skeptics a vote of thanks for making our science as precise as it is today," says Mayewski.

One big supporter of climate science research is the Bush administration, spending $5 billion a year. But Mr. Bush refuses to sign a treaty forcing cuts in greenhouse gases.

The White House also declined 60 Minutes' request for an interview. Corell, who first studied the issue for President Reagan, believes the climate change facts are in, even if President Bush does not.

"When you look at the American government, which is saying essentially, 'Wait a minute. We need to study this some more. We can't flip our energy use overnight. It would hurt the economy.' When you hear that, what do you think?" Pelley asked.

"Well, what I do then is, I try to tell them exactly what we know scientifically. The science is, I believe, unassailable," says Corell. "I'm not arguing their policy, that's their business, how they deal with policy. But my job is to say, scientifically, shorten that time scale so that if you don't push out the effects of climate change into the long, long distant future. Because even under the best of circumstances, this natural system of a climate will continue to warm the planet for literally hundreds of years, no matter what we do."
By Bill Owens