"Fahrenheit 911" may be the dominant campaign movie of 2004, but several other overtly political films have been making the rounds as well. My favorite is "The Day After Tomorrow," in which a climatologist tries to figure out a way to save the world from abrupt global warming.

How abrupt?  It happens over the weekend, more or less -- quick enough to kill the gallant data collectors in Scotland who at least get off a helpful warning before they freeze.

First the West Antarctic Ice Sheet falls into the sea. Then the great south-to-north current known as the Gulf Stream reverses itself, plunging America's East Coast and Northern Europe into a new ice age. Giant tornadoes form, conducting frigid air from the mesosphere to the surface of the earth, freeze-drying all those who are unlucky enough to get in their way.

Whereupon the hero snowshoes from Philadelphia to New York in a blizzard, to rescue his teenage son, who is marooned with his friends in the New York Public Library. They keep warm by burning books, while resurgent wolves howl aboard a oil tanker caught in the Fifth Avenue ice just outside.

Meanwhile, the villain, a go-it-alone, highly skeptical vice president of the United States, played by a Dick Cheney look-alike, takes over when the president is killed in an ice storm, and -- at last! -- pledges in an address to the people of the world to do all he can to arrest the damage that generous subsidies to the energy industries have done.

Great stuff!  But it bears as much relation to what we think of as plausible reality as do "Jurassic Park" and "Asteroid," (equally silly movies whose formula it closely follows.)  The ice sheet collapse and the Gulf Stream catastrophe turn out to be real enough possibilities, though no one knows how likely they are occur in the next century or two. Hollywood reads the scientific journals -- but just long enough to get a few controversial new ideas about the Next Big Threat.

Yet "The Day After Tomorrow" is not altogether to be despised. It comes at a time when many other nagging symptoms (the surging price of oil, every little unexpected variation in weather patterns) remind us that, in scientific circles, the verdict is in.

Global warming is underway. In 2001, the Intergovernmental Panel on Climate Change, the senior world body studying the change, firmly declared that greenhouse warming would steadily get worse for the rest of our lifetimes, no matter what we do next.

The real questions are: How much worse?  What should we do about it? 

An antidote to the sensationalism is a very useful book that has just appeared in paperback, The Discovery of Global Warming by Spencer R. Weart. It costs no more than would have a couple of tickets to "The Day After Tomorrow" (the flick is already in the basement, having left the theaters last month for the rental market).

Discovery offers a summary of nearly all that can be known about global warming today, in 201 easy-to-read pages ­ an introduction to the problem connected to an intricately-linked Website that offers another couple dozen essays and a thousand-item bibliography.

More to the point, however, the book satisfies the ever-present, sometimes overwhelming human craving for narrative. That is, it defies scientific convention to construct a story, a chronicle of "how a few people, through ingenuity, stubborn persistence, and a bit of luck, came to understand a grave problem even before any effects became manifest."

What people? Weart identifies for special attention a handful of key personal stories from the tapestry of a century of increasingly complex science.

There is Svante Arrhenius, for example. In the late 19th century, iIce ages were a fashionable topic, for their existence had been discovered barely a century before. What had been their cause?  Could one happen again?

Arrhenius already knew of the opacity of carbon dioxide and methane gas to infra-red radiation; their "greenhouse " property had been discovered in 1859.

But the Swedish scientist in 1896 was the first to include increased humidity in his laborious calculations ­ with the surprising result that global climate might as easily heat up by several degrees as cool off. A mere doubling of carbon dioxide could raise temperatures by five or six degrees. Arrhenius had "not quite discovered global warming," writes Weart, but he had uncovered for the first time a "curious theoretical concept."

On the other hand, his findings persuaded hardly anyone.  They were as quickly dismissed by well-established scientists as was the equally quaint argument that the continents were slowly moving around on the surface of the earth.

For not only did the first cursory laboratory tests of the hypothesis raise doubts about the magnitudes involved. The very idea that humankind could interfere with the essential stability of nature contradicted deeply ingrained beliefs of the scientific community, as did the idea that such change could happen swiftly -- catastrophically, rather than at a uniform pace. Arrhenius' hypothesis was dismissed.  

Still, there was the pesky evidence of those long-ago ice ages. 

Between the world wars, various investigators added various pieces to the puzzle. A Serbian engineer named Milutin Milankovitch tried to prove that regular perturbations in the earth's orbit were the root cause.

Others worked on sunspots -- variations in the flow of solar energy -- as the source of the periodic cooling of the earth, or the possibility that massive eruptions of volcanic dust were to blame. (One such widely-noted eruption had led to a famous "year without a summer" in 1816 in New England.)

It was only after World War II that the modern scientific understanding of global climate change began to emerge -- often under the aegis of military funders interested in more precisely forecasting the weather, or even controlling it in order to employ it as a weapon. And these are the stories on which Weart lavishes his careful attention.

How Charles Keeling established a monitoring station for carbon dioxide atop the extinct Mauna Loa volcano in Hawaii, thousands of miles from any significant economic activity, in order to determine with unassailable precision whether greenhouse gases in the atmosphere truly were increasing. (They are, and have been without interruption for at least a half century.)

How Reid Bryson in the 1960s, using samples of ancient pollen, demonstrated that a pattern of "punctuated equilibrium" had obtained in the weather of the past -- long periods of relative stability followed by dramatic shifts, taking no longer than a century or two. How he then popularized his views in a series of dramatic warnings in the 1970s that humankind might soon be running out of food, earning (with many others) a reputation as an eco-radical. How other scientists in the 1970s then puzzled over the intricate relationships between deforestation and agriculture and carbon dioxide fertilization and ocean uptake.

How a weather-modeling group originally founded by polymath genius John Von Neumann gradually developed the first models of global circulation, gradually extending their competence in tandem with the computational revolution until they were able to build passable models of seasonal variation.  How their small successes gave rise to the growing recognition that their problems were surpassingly complex, culminating in Edward Lorenz' famous koan, "Does the flap of a butterfly's wings in Berlin set off a tornado in Texas?" 

How scientists from a dizzying array of disciplines -- oceanographers and astronomers, geologists and botanists, chemists and mathematicians, population biologists and pollution experts, geophysicists and computer scientists -- gradually learned to make common cause on climate issues. How Bert Bolin, a Swedish climatologist and expert scientific diplomat, launched first the Global Atmospheric Research Program in the late 1960s and then, twenty years later, called into being the Inter-Governmental Panel on Climate Change -- some 200 scientists, organized in a dozen workshops, representing not just their respective disciplines but their governments as well, the ultimate consensus-building body. 

For the telling of this tale, author Weart is well-suited by both temperament and background knowledge.  Trained as a solar physicist at Cornell University and the University of Colorado at Boulder in the 1960s, he worked for a time at Cal Tech on building a large solar telescope, then retooled in the early 1970s as an historian of science at the University of California at Berkeley.

As director of the Center for the History of Physics of the American Institute of Physics since 1974, he has written a number of books, including two for children. He worked on and off on The Discovery of Global Warming for most of fifteen years.

"You have to understand," he says, "first I wrote a website. Then I destroyed it by putting it in this highly linear form." As many names as are included in his account, he clearly feels badly about every name left out. No one person made the discovery of global warming. Rather it was the linking-up of a large number of previously isolated scientific communities. "You can't point to a single observation or model that convinced everybody about anything."

The advance of science, especially this kind of science, does not resemble the members of a Lewis and Clark expedition peering into a previously unknown valley for the first time.  Instead, he write, the scientific scene "looks more like a crowd of people scurrying about, some huddling together to exchange notes, others straining to hear a distant voice or shouting criticism across the hubbub. Everyone is moving in different directions and it takes a while to see the overall trend."  It is not the sort of thing that lends itself to a two-hour movie -- or even a 200-page book

But thanks to scientific traditions -- fact-gathering, rational discussion, toleration of dissent and the pursuit of an evolving consensus -- the overall trend in science is very powerful.  When it finally emerges, it borders on certainty. Today, he writes,

"The hypothesis proposed by Arrhenius in 1896 -- denied by almost every expert during the first half of the twentieth century and steadily advancing through the second half -- was now as well accepted as any scientific proposal of its nature ever could be."