The Paul Revere of global warming.

James E. Hansen is the Paul Revere of global warming. The director of NASA's Goddard Institute for Space Studies in New York City since 1981, Hansen was in the news last year when the White House saddled him with a twenty-four-year-old media handler, who ordered Hansen to clear all his statements first. Sixty-four at the time, Hansen had been waging weather wars since before his minder was born. Resisting the gag order, Hansen ultimately prevailed.

Six feet tall, with receding, light-brown hair, Hansen favors plaid shirts that would put him at home on an Iowa farm, which is where he was born. Growing up in Denison, about sixty miles northeast of Omaha, Nebraska, Hansen was the fifth of seven children (he has four older sisters). Hansen's father, a tenant farmer, moved to Denison when Jim was four years old, and took up work as a bartender; his mother worked as a waitress.

With a scholarship and money saved from his Omaha World-Herald paper route, Hansen attended the University of Iowa, graduating summa cure laude in 1963, while majoring in mathematics and physics. Hansen then earned a master's degree in astronomy there.

The University of Iowa was an exciting place to study astronomy. The department had its own satellite, and its chairman was James Van Allen, who discovered the Earth-girdling radiation belts that later were named after him. "I was so shy and unconfident that when I had an opportunity to take a course under Professor Van Allen, I avoided it because I didn't want him to realize how ignorant I was," Hansen told an audience at his alma mater in 2004.

Hansen decided to specialize in the atmosphere of Venus at a time when scientists were discovering that the planet's super-hothouse atmosphere (with temperatures above 850 Fahrenheit) was 95 percent carbon dioxide. He earned a doctorate in 1967 with a dissertation on Venus and then went to work at the Goddard Institute.

Hansen's interest in global warming began accidentally. In 1976, he was serving as a principal investigator on the Pioneer Venus Orbiter when a Harvard postdoctoral researcher asked him to help calculate the greenhouse effect of human-generated emissions on the Earth's atmosphere. Even since, Hansen has immersed himself in the problem, and he has not minced words about global warming's dangers.

In 1981, Hansen, with several Goddard colleagues, was the first to use the term "global warming" in a scientific context. Following an important article in Science, Reagan Administration functionaries withdrew Goddard's funding from the Energy Department.

In 1988, with George H. W. Bush in the White House, Hansen went public with warnings about global warming before the U.S. Senate, on a very hot, humid summer day in Washington, D.C., part of a notably hot summer nationwide.

"The greenhouse effect has been detected, and it is changing our climate now," he testified, anticipating an increased frequency of extreme climatic events.

Critics accused him of crying wolf. But he had a ready response.

"When is the proper time to cry wolf?" Hansen asked in John J. Nance's What Goes Up: The Global Assault on Our Atmosphere. "Must we wait until the prey, in this case the world's environment, is mangled by the wolf's grip?"

Now, as he faces off against an Administration known for protecting its fossil-fuel interests, Hansen is holding his ground. He has compared the censorship of science under Bush to the distortion of science under Stalin. Even before getting a minder, Hansen was having trouble. By 2004, the White House was reviewing climate-related press releases, imposing gridlock that often delayed news a month or more.

A speech he planned to give in Washington, D.C., sponsored by Resources for the Future, was cancelled a week before the 2004 election. Hansen has no direct evidence of White House pressure, although an explanation he received did refer to the election. Hansen surmised (as he explained in an e-mail) that the group had a case of pre-election skittishness. "They realized Bush was probably going to win the election, so why risk retaliation?"

Hansen then called on Van Allen, who, now more than ninety years of age, has retired from the University of Iowa. Colleagues at Iowa told Hansen that Van Allen was happy to welcome him home. The influence of Hansen's mentor was still strong. As Hansen told the Bergen (New Jersey) Record, Van Allen himself often had differed with government officials, and the senior scientist told him, "I know that my positions have not endeared me to people at NASA headquarters, but I take the position that I'm dealing with honorable men. It's a good attitude."

Van Allen arranged for Hansen to give a public presentation in Iowa City. "This process [of censorship] is in direct opposition to the most fundamental precepts of science," said Hansen, speaking explicitly as a private citizen. "This, I believe, is a recipe for environmental disaster."

Every month, Hansen's lab takes the Earth's temperature, monitoring 10,000 temperature gauges around the planet. Year by year, the average temperature rises. Last year was the warmest yet--a fact that his superiors, at one point, told him not to release. Hansen's office released the data anyway.

At the American Geophysical Union annual meeting in San Francisco last December, Hansen addressed a basic question: How much "wiggle room" does the Earth and its inhabitants have before global warming becomes a truly unavoidable disaster?

Further warming of more than 1 degree Celsius "will make the Earth warmer than it has been in a million years," Hansen said. If we continue with business as usual, he said, we will see "changes that constitute practically a different planet.... The Earth's climate is nearing, but has not passed, a tipping point, beyond which it will be impossible to avoid climate change with far-ranging undesirable consequences."

What will that "different planet" look like? At the American Geophysical Union meeting, Hansen spelled it out: "Not only loss of the Arctic as we know it, with all that implies for wildlife and indigenous peoples, but losses on a much vaster scale due to worldwide rising seas." Many coastal cities--Shanghai, New York, London, and Calcutta, to name a few--will be in peril. Hansen cannot tell us exactly when the toilets will back up at the White House (about fifty feet above sea level), but if we don't cut our fossil fuel consumption soon, they will. The question is when.

Hansen said there remains time to avoid climatic calamity. He gives us a decade, maybe two, to reach the "tipping point."

"Strong policy leadership and international cooperation" will be necessary, he told the geophysicists, but that has not been forthcoming from the Bush White House. Hansen emphasized that special interests are "a roadblock wielding undue influence over policymakers." These special interests, he says, "seek to maintain short-term profits with little regard to either the long-term impact on the planet that will be inherited by our children and grandchildren or the long-term economic well-being of our country."

It was after this presentation that Hansen was assigned George Deutsch, the young political operative, to manage his media relations. Deutsch's supposed journalism degree from Texas A & M quickly was exposed as a fraud, and he was forced to resign, meanwhile pouting that he had been a victim of a Democrat ambush. Deutsch's qualification for the job was his service on the Bush-Cheney reelection campaign.

Hansen himself is a political independent who readily acknowledges that he voted for John Kerry in 2004. After the Deutsch scandal, NASA issued new rules protecting the rights of scientists to communicate their work to the public.

As Hansen was evading his minder at NASA, he was receiving reports in the journal Science that the melting of the Greenland ice cap has been accelerating markedly, suggesting that existing estimates of future sea-level rise are too low.

"How long have we got?" Hansen asked in a piece published on the front page of the London Independent on February 17, 2006. "We have to stabilize emissions of carbon dioxide within a decade. We cannot wait for new technologies like capturing emissions from burning coal. We have to act with what we have. This decade, that means focusing on energy efficiency and renewable sources of energy that do not burn carbon. We don't have much time left."

According to Mark Bowen in Thin Ice, Hansen enjoys reading fiction with heroes who flout convention and are persecuted for sticking to their principles. Asked for specifics in an e-mail, Hansen said he had in mind Elizabeth of Pride and Prejudice and Tom Joad from Grapes of Wrath.

Hansen maintains an extensive e-mail list of people to whom he sends early drafts of his papers, asking for criticism. (I'm honored to be on that list.) On March 13, Hansen sent a letter to his correspondents observing that the ideological weather improved at NASA after he went public. At the EPA, however, "where double-speak ('sound science,' 'clear skies') has achieved a level that would make George Orwell envious, [the situation] is much bleaker, based on the impression that I receive from limited discussion with colleagues there," Hansen wrote. But Hansen averred that, "unless some new event demands it," he would like to avoid whistle-blowing activities in favor of full-time science so he could get back to his task of "quantifying options for dealing with global warming."

With that, Hansen returned to the lab--until the next time.

Illustration by Tomasz Walenta

Bruce E. Johansen, Frederick W. Kayser Professor of Communication at the University of Nebraska at Omaha, is author of the three-volume "Global Warming in the Twenty-first Century" (Praeger, 2006).