Asked if he believes the administration is censoring what he can say to the public, Hansen says: "Or they're censoring whether or not I can say it. I mean, I say what I believe if I'm allowed to say it."

What James Hansen believes is that global warming is accelerating. He points to the melting arctic and to Antarctica, where new data show massive losses of ice to the sea.

Is it fair to say at this point that humans control the climate? Is that possible?

"There's no doubt about that, says Hansen. "The natural changes, the speed of the natural changes is now dwarfed by the changes that humans are making to the atmosphere and to the surface."

Those human changes, he says, are driven by burning fossil fuels that pump out greenhouse gases like CO2, carbon dioxide. Hansen says his research shows that man has just 10 years to reduce greenhouse gases before global warming reaches what he calls a tipping point and becomes unstoppable. He says the White House is blocking that message.

"In my more than three decades in the government I've never witnessed such restrictions on the ability of scientists to communicate with the public," says Hansen.

Restrictions like this e-mail Hansen's institute received from NASA in 2004. "… there is a new review process … ," the e-mail read. "The White House (is) now reviewing all climate related press releases," it continued.

Why the scrutiny of Hansen's work? Well, his Goddard Institute for Space Studies is the source of respected but sobering research on warming. It recently announced 2005 was the warmest year on record. Hansen started at NASA more than 30 years ago, spending nearly all that time studying the earth. How important is his work? 60 Minutes asked someone at the top, Ralph Cicerone, president of the nation's leading institute of science, the National Academy of Sciences.

"I can't think of anybody who I would say is better than Hansen. You might argue that there's two or three others as good, but nobody better," says Cicerone.

And Cicerone, who's an atmospheric chemist, said the same thing every leading scientist told 60 Minutes.

"Climate change is really happening," says Cicerone.

Asked what is causing the changes, Cicernone says it's greenhouse gases: "Carbon dioxide and methane, and chlorofluorocarbons and a couple of others, which are all - the increases in their concentrations in the air are due to human activities. It's that simple."

But if it is that simple, why do some climate science reports look like they have been heavily edited at the White House? With science labeled "not sufficiently reliable." It's a tone of scientific uncertainty the president set in his first months in office after he pulled out of a global treaty to reduce greenhouse gas emissions.

"We do not know how much our climate could, or will change in the future," President Bush said in 2001, speaking in the Rose Garden of the White House. "We do not know how fast change will occur, or even how some of our actions could impact it."

Annoyed by the ambiguity, Hansen went public a year and a half ago, saying this about the Bush administration in a talk at the University of Iowa: "I find a willingness to listen only to those portions of scientific results that fit predetermined inflexible positions. This, I believe, is a recipe for environmental disaster."

Since then, NASA has been keeping an eye on Hansen. NASA let Pelley sit down with him but only with a NASA representative taping the interview. Other interviews have been denied.

"I object to the fact that I'm not able to freely communicate via the media," says Hansen. "National Public Radio wanted to interview me and they were told they would need to interview someone at NASA headquarters and the comment was made that they didn't want Jim Hansen going on the most liberal media in America. So I don't think that kind of decision should be made on that kind of basis. I think we should be able to communicate the science."

Politically, Hansen calls himself an independent and he's had trouble with both parties. He says, from time to time, the Clinton administration wanted to hear warming was worse that it was. But Hansen refused to spin the science that way.

"Should we be simply doing our science and reporting it rigorously, or to what degree the administration in power has the right to assume that you should be a spokesman for the administration?" asks Hansen. "I've tried to be a straight scientist doing the science and reporting it as best I can."

Dozens of federal agencies report science but much of it is edited at the White House before it is sent to Congress and the public. It appears climate science is edited with a heavy hand. Drafts of climate reports were co-written by Rick Piltz for the federal Climate Change Science Program. But Piltz says his work was edited by the White House to make global warming seem less threatening.

"The strategy of people with a political agenda to avoid this issue is to say there is so much to study way upstream here that we can't even being to discuss impacts and response strategies," says Piltz. "There's too much uncertainty. It's not the climate scientists that are saying that, its lawyers and politicians."

Piltz worked under the Clinton and Bush administrations. Each year, he helped write a report to Congress called "Our Changing Planet."

Piltz says he is responsible for editing the report and sending a review draft to the White House.

Asked what happens, Piltz says: "It comes back with a large number of edits, handwritten on the hard copy by the chief-of-staff of the Council on Environmental Quality."

Asked who the chief of staff is, Piltz says, "Phil Cooney."

Piltz says Cooney is not a scientist. "He's a lawyer. He was a lobbyist for the American Petroleum Institute, before going into the White House," he says.

Cooney, the former oil industry lobbyist, became chief-of-staff at the White House Council on Environmental Quality. Piltz says Cooney edited climate reports in his own hand. In one report, a line that said earth is undergoing rapid change becomes "may be undergoing change." "Uncertainty" becomes "significant remaining uncertainty." One line that says energy production contributes to warming was just crossed out.

"He was obviously passing it through a political screen," says Piltz. "He would put in the word potential or may or weaken or delete text that had to do with the likely consequence of climate change, pump up uncertainty language throughout."

In a report, Piltz says Cooney added this line "… the uncertainties remain so great as to preclude meaningfully informed decision making. …" References to human health are marked out. 60 Minutes obtained the drafts from the Government Accountability Project. This edit made it into the final report: the phrase "earth may be" undergoing change made it into the report to Congress. Piltz says there wasn't room at the White House for those who disagreed, so he resigned.

"Even to raise issues internally is immediately career limiting," says Piltz. "That's why you will find not too many people in the federal agencies who will speak freely about all the things they know, unless they're retired or unless they're ready to resign."

Jim Hansen isn't retiring or resigning because he believes earth is nearing a point of no return. He urged 60 Minutes to look north to the arctic, where temperatures are rising twice as fast as the rest of the world. When 60 Minutes visited Greenland this past August, we saw for ourselves the accelerating melt of the largest ice sheet in the north.

"Here in Greenland about 15 years ago the ice sheet extended to right about where I'm standing now, but today, its back there, between those two hills in the shaded area. Glaciologists call this a melt stream but, these days, its a more like a melt river," Pelley said, standing at the edge of Greenland's ice sheet.

The Bush administration doesn't deny global warming or that man plays a role. The administration is spending billions of dollars on climate research. Hansen gives the White House credit for research but says what's urgent now is action.

"We have to, in the next 10 years, get off this exponential curve and begin to decrease the rate of growth of CO2 emissions," Hansen explains. "And then flatten it out. And before we get to the middle of the century, we've got to be on a declining curve.

"If that doesn't happen in 10 years, then I don't think we can keep global warming under one degree Celsius and that means we're going to, that there's a great danger of passing some of these tipping points. If the ice sheets begin to disintegrate, what can you do about it? You can't tie a rope around the ice sheet. You can't build a wall around the ice sheets. It will be a situation that is out of our control."

But that's not a situation you'll find in one federal report submitted for review. Government scientists wanted to tell you about the ice sheets, but before a draft of the report left the White House, the paragraph on glacial melt and flooding was crossed out and this was added: "straying from research strategy into speculative findings and musings here."

Hansen says his words were edited once during a presentation when a top official scolded him for using the word danger.

"I think we know a lot more about the tipping points," says Hansen. "I think we know about the dangers of even a moderate degree of additional global warming about the potential effects in the arctic about the potential effects on the ice sheets."

"You just used that word again that you're not supposed to use - danger," Pelley remarks.

"Yeah. It's a danger," Hansen says.

For months, 60 Minutes had been trying to talk with the president's science advisor. 60 Minutes was finally told he would never be available. Phil Cooney, the editor at the Council on Environmental Quality didn't return 60 Minutes' calls. In June, he left the White House and went to work for Exxon Mobil.

"The style of the decoration is unique, not so much from an artistic point of view, but for the subject and the colors used," said Pavlos Flourentzos, director of the island's antiquities department.

Only two similar sarcophagi have ever been discovered in Cyprus before. One is housed in New York's Metropolitan Museum of Art and the other in the British Museum in London, but their colors are more faded, Flourentzos said.

Flourentzos said the coffin _ painted in red, black and blue on a white background _ dated to 500 B.C., when Greek cultural influence was gaining a firm hold on the eastern Mediterranean island. Pottery discovered in the tomb is expected to provide a precise date.

Experts believe the ornate decoration features the hero Ulysses in scenes from Homer's Iliad and Odyssey _ both hugely popular throughout the Greek world.

In one large painting, Ulysses and his comrades escape from the blind Cyclops Polyphemos' cave, hidden under a flock of sheep. Another depicts a battle between Greeks and Trojans from the Iliad.

Archeologists think the scenes hint at the status of the coffin's occupant.

"Why else take these two pieces from Homer and why deal with Ulysses? Maybe this represents the dead person's character _ who possibly was a warrior," Flourentzos said.

Other drawings depict a figure carrying a seriously injured or dead man and a lion fighting a wild boar under a tree. These are not believed to be linked with Homer's poems.

Reflecting a long oral tradition loosely based on historic events, Homer's epics were probably composed around 800 B.C. and written down in the 6th century B.C.

The tomb was found in an area containing several ancient cemeteries which belonged to the nearby town of Palaepaphos, 11 miles inland from modern Paphos.

First settled around 2800 B.C., Palaepaphos was the site of a temple of Aphrodite _ the ancient goddess of beauty who, according to mythology, was born in the sea off Paphos.

McGaugh's journey through an intellectual purgatory began six years ago when a woman now known only as AJ wrote him a letter detailing her astonishing ability to remember with remarkable clarity even trivial events that happened decades ago.

Give her any date, she said, and she could recall the day of the week, usually what the weather was like on that day, personal details of her life at that time, and major news events that occurred on that date.

Like any good scientist, McGaugh was initially skeptical. But not anymore.

"This is real," he says.

Soon after AJ took over his life, McGaugh teamed with two fellow researchers at the University of California at Irvine. Elizabeth Parker, a clinical professor of psychiatry and neurology (and lead author of a report on the research in the current issue of the journal Neurocase), and Larry Cahill, an associate professor of neurobiology and behavior, have joined McGaugh in putting AJ through an exhaustive series of interviews and psychological tests. But they aren't a lot closer today to understanding her amazing ability than they were when they started.

"We are trying to find out, but we haven't hit 'bingo' yet," says McGaugh.

His initial hypothesis, like several others, has turned out to be wrong - or at least incomplete.

McGaugh has spent decades studying how such things as stress hormones and emotions affect memory, and at first he thought AJ's memories were of such emotional power that she couldn't forget them.

But that hypothesis fell short of the mark when it became obvious that "the woman who can't forget" remembers trivial details as clearly as major events. Asked what happened on Aug 16, 1977, she knew that Elvis Presley had died, but she also knew that a California tax initiative passed on June 6 of the following year, and a plane crashed in Chicago on May 25 of the next year, and so forth. Some may have had a personal meaning for her, but some did not.

"Here's a woman who has very strong memories, but she has very strong memories of things for which I have no memory at all," McGaugh says.

That became particularly clear one day when he asked her out of the blue if she knew who Bing Crosby was.

"I wasn't sure she would know, because she's 40 and wasn't of the Bing Crosby era," he says.

But she did.

"Do you know where he died?" McGaugh asked.

"Oh yes, he died on a golf course in Spain," she answered, and provided the day of the week and the date when the crooner died.

When the researchers asked her to list the dates when they had interviewed her, she "just reeled them off, bang, bang, bang."

She also told McGaugh that on the day after a particular interview, which took place several years ago, he flew to Germany.

"I said what? I went to Germany? I couldn't even remember what year I had gone to Germany," he says.

That level of recall suggests another hypothesis. Some people are able to recall past events by categorizing them. Certain events, or facts, are associated with others, and filed away together so that they may be easier to access. That's a trick that is often used by entertainers who use feats of memory to wow their audience.

AJ does have "some sort of compulsive tendencies. She wants order in her life," McGaugh says. "As a child, she would get upset if her mother changed anything in her room because she had a place for everything and wanted everything in its place.

"So she does categorize events by the date, but that doesn't explain why she remembers it."

Also, her degree of recall is so much greater than any other person's in the scientific literature that it seems unlikely to be the complete answer, McGaugh adds.

She is also quite different from savants who have surfaced from time to time with extraordinary abilities in music, art or memory.

"Some of them can remember every single detail about the particular hobby that they have, such as baseball or calendars or art, but they are very narrow," he says. McGaugh described one person who could memorize a piece of music instantly, and not forget it, but who "couldn't make change or couldn't take a bus because he didn't know where he was."

By contrast, AJ is a " fully functioning person," McGaugh says.

The researchers are preparing to take their work in a new direction in hopes of understanding what is going on here. It's possible AJ's brain is wired differently, and that may show up through magnetic resonance imaging. Testing is expected to begin within six months.

"We will be looking at her brain, using brain scanning techniques, to see if there's anything that is dramatically different that we can point to," McGaugh says.

Those of us with normal, very fallible memories function somewhat like a computer in that different areas of our brains are interconnected and thus better-suited for general memories. We know where we live and how to get to work, but we may not know what the weather was like on this date four years ago.

It's possible that AJ's brain has some "disconnections" that help her recall past events from her memory bank without interference from the parts of her brain that act as general processors. But the problem is that even if they find some interesting wiring through brain scans, the researchers will be limited in their conclusions by the fact that AJ seems to be unique.

So unique, in fact, that the Irvine team has given her condition a new name. They call it hyperthymestic syndrome, based on the Greek word thymesis for "remembering" and hyper, meaning "more than normal."

Some day, the researchers say, they hope to know what's different about AJ's brain, but they are still a ways off.

"In order to explain a phenomenon you have to first understand the phenomenon," McGaugh says. "We're at the beginning."

Now, the "cenotes," deep sinkholes in limestone that have pools at the bottom, are yielding scientific discoveries including possible life-saving cancer treatments.

Divers are dipping into the cenotes, which stud the Yucatan peninsula, to explore a vast underground river system.

Hefting air tanks, guidelines and waterproof lamps, they have so far mapped 405 miles of channels that form part of a huge subterranean river delta flowing into the Caribbean sea, and they are only just starting.

Scientists investigating the network of caverns and galleries, formed by rainwater passing through porous limestone, have found a wealth of early archeological relics and prehistoric animal bones.

They also have identified dozens of new aquatic species specially adapted to extreme environmental conditions which could have medical applications.

In the Riviera Maya, a strip of Caribbean tourist resorts including the world-famous archeological site of Tulum, there are more than 500 cenotes. Some are open to the jungle, while others have tiny eye-like holes letting in sunlight and jungle roots.

Their waters have filtered through sponge-like limestone which leaves them so transparent that divers say they feel like they are floating in space. The pools range in depth from a few feet (a meter) to an abyss where explorers have still not touched bottom at over 500 feet.

"It is proving to be a totally unique environment," said marine biologist Tom Iliffe of Texas A&M University. "We are finding things down there including forms of life that no one had ever guessed existed, and there is a lot more work to be done."

BLIND FISH AND MAMMOTHS

The Yucatan sits on a limestone plateau where rainwater percolates down to nonporous rock below ground. Over millions of years, underground river systems have formed that flow out to the sea through caves.

The region's 7,000 to 8,000 cenotes were formed when caves collapsed in on themselves. The resulting sinkholes became a vital water source and a focus for Mayan sacrifices to honor Chac, the volatile, crocodile-like rain deity.

In recent years, biologists delving into the underlying river systems, which unlike the sinkholes are jet-black because of the lack of sunlight, have identified 40 entirely new species, mostly blind shrimps and fish which have adapted to life in the system's harsh conditions, where dissolved oxygen and food are scarce.

Among the startling discoveries are microorganisms that live in the transitional zone where the fresh water rivers flow out into the Caribbean, and salt-water sponges which may contain anti-tumor compounds.

"Research is at an early stage, but it is quite possible that the bacteria and sponges may have potential biomedical applications including cures for cancer," Iliffe told Reuters in a telephone interview. "There is a great deal of scientific excitement about it."

Other finds made by divers roaming the deep, dark corridors include the bones of giant jungle sloths, rabbits and even mammoths dating back beyond the last Ice Age.

"When you come up and tell people there are elephants down there they really think you've gone crazy," said Sam Meacham, an underwater explorer and conservationist.

THREATENED BY DEVELOPMENT

In the past three decades the population of the Riviera Maya has soared 10-fold to close to 1 million people, as tourists from the United States, Europe and Mexico flock to the palm-fringed strip to soak up the sun.

Environmentalists say that the explosive development has been only patchily regulated and warn that waste produced by resort hotels and service towns in the area is already polluting the complex underground oasis.

"It's totally the Wild West, when what is needed is carefully planned, sustainable development," said Meacham, who runs the Quintana Roo Water Systems Research Center, a local non-profit group that raises consciousness about water issues in schools.

Water conservation will be a key issue when ministers, hydrologists and environmentalists from around the world meet at the World Water Forum in Mexico City from March 16-22.

Meacham says human sewage is pumped deep underground, and that at least one water system in the Yucatan has been polluted with fecal matter. The impact of 250 tonnes of trash dumped in landfills each day has yet to be evaluated.

The hundreds of tourists who dive and snorkel each day in any of a dozen cenotes and caves open to the public are also unwittingly destroying the ecosystems before they can be properly understood, Iliffe says.

"Fish are following the divers into the caves and they gobble up all the life, and they (the caves) are left biologically sterile," he said.

"When you consider that they could possibly lead to a cure for cancer, it is essential to conserve them."