Unit 5 The global warningThe North Pole has been frozen for 100,000 years. But according to scientists, that wont be true by the end of this century. The top of the world is melting.Theres been a debate burning for years about the causes of global warming. But the scientists youre 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 evidence was compiled by American scientist Bob Corell, who led a study called the Arctic Climate Impact Assessment. Its 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. What does the melting arctic look like? Correspondent Scott Pelley went north to see what Bob Corell calls a global warning.Towers of ice the height of 10-story buildings rise on the coast of Greenland. Its the biggest ice sheet in the Northern Hemisphere, measuring some 700,000 square miles. But temperatures in the arctic are rising twice as fast as the rest of the world, so a lot of Greenlands ice is running to the sea.Right now the entire planet is out of balance, says Bob Corell, who is among the worlds top authorities on climate change. He led 300 scientists from eight nations in the Arctic Climate Impact Assessment. Corell believes he has seen the future. This is a bellwether, a barometer. Some people call it the canary in the mine. The warning that things are coming, he says. In 10 years here in the arctic, we see what the rest of the planet will see in 25 or 35 years from now.Over the last few decades, the North Pole has been dramatically reduced in size and Corell says the glaciers there have been receding for the last 50 years.Back in 1987, President Reagan asked Corell to look into climate change. Hes been at it ever since. In Iceland, he showed 60 Minutes glaciers that were growing until the 1990s and are now melting. In fact, 98 percent of the worlds mountain glaciers are melting.Corell says all that water will push sea levels three feet higher all around the world in 100 years. You and I sit here, another foot. Your children, another foot. Your grandchildren, another foot. And it wont take long for sea level to inundate, says Corell. Sea level will be inundating the low lands of virtually every country of the world, ours included, Corell predicts.To find the sights and sounds of the arctic melting, there are few places better than a fjord in 精选文档Greenland, with a glacier just a short distance away.Pelley stood on a huge block of ice that had split off from the glacier and had dropped into the sea a big iceberg. This part of Greenland is melting faster than just about any other. To get a sense of the enormity of whats happening, consider this: The ice that is melting here is the equivalent of all the ice in the Alps, Pelley explained, standing atop the iceberg.Thats more than 105 million acres of melted ice in 15 years. Just four minutes after Pelley cleared off this berg, part of the ice caved in.60 Minutes got a birds-eye view of how unstable the ice is becoming on a flight with glaciologist Carl Boggild. Boggild anchored 10 research stations to the ice. But every time he comes to visit, the ice and his stations have moved.Flying over the ice, Pelley noticed lots of fissures and crevices breaking through the ice.Asked what causes this, Boggild explained, This is actually the ice flow, where you have so much tension in the ice that it cannot stick together. And it breaks and opens a crevice which goes about 150, 200 feet down.The ice is also melting on the sides, Boggild says.High overhead, Pelley remarked that one could hear the water running. Its like a small river, Boggild said.A leading theory says those little rivers lubricate the bottom of the ice sheet, helping it move off the bedrock and out to sea. And there may be no stopping it. Arctic warming is accelerating. Its a chain reaction. As snow and ice melt they reveal dark land and water that absorb solar heat. That melts more snow and ice, and around it goes.精选文档Theres long been a debate about how much of this is earths naturally changing climate and how much is mans 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