Scientists and government officials from 130 countries will gather here this week to forge a world response to a threat that some regard as a potential nightmare and others consider a mere inconvenience.
Despite attempts at consensus, researchers are still deeply divided over global warming and its potential impact and say it could be a decade before they have the answers to such critical questions as whether rising temperatures will cause the seas to rise.
Yet this week's conference reflects the fact that many experts feel some action must be taken before anything definitive is known.
"I believe the greenhouse is coming and I believe it is going to be a serious problem," said Richard Alley of Pennsylvania State University, a world authority on reading past climates in ancient ice. "Yet by the time we can with confidence say that the greenhouse is here, it will be too late."
Delegates will be pressed to follow the lead of European nations that have already pledged to reduce emissions of carbon dioxide. The gas, produced by burning fossil fuels, plays an integral part in computer-generated scenarios predicting a worldwide warming of 6 degrees by the end of the next century.
The Bush administration has resisted such calls in the past and insisted that more research is needed before the United States undertakes the kind of disruptive changes that cutting carbon dioxide emissions would involve.
While scientists generally support attempts to increase energy efficiency and to move away from fossil fuels and toward renewable energy, many of them also shy away from recommendations that would cost large sums or disrupt the economy.
"There are tremendous uncertainties that led me to say that tremendous costs are unwarranted at present," said Patrick Michaels, a climatologist at the University of Virginia and a skeptic of scenarios that predict significant warming.
The reluctance of most researchers to call for stringent controls of carbon dioxide stems from the fact that the greenhouse debate is still very much alive. Policy-makers and the public are left to sort through the bewildering cross talk that occurs when scientific cultures and personalities collide.
"There is a selective use of facts. Nobody tells an untruth. But nobody tells the whole truth, either," said S. Fred Singer, an atmospheric and space physicist at the Washington Institute here. "It all depends on the ideological outlook."
Singer said the greenhouse effect has been used by all sorts of interest groups to further their agendas. "My nuclear friends are happy to promote the greenhouse effect. My natural gas friends are happy to promote the greenhouse effect," Singer said. "A lot of scientists promote the greenhouse effect because of increased funding."
"The public is rightly confused," said Stephen Schneider, a climatologist at the National Center for Atmospheric Research in Colorado. "The good thing about science is that scientists argue. But the public doesn't understand that. They think that because scientists argue, they don't know what they're talking about."
Schneider maintains that scientists generally agree on the basics of global warming. Indeed, in almost two dozen interviews with scientists who study all aspects of climate change, there was general agreement that the accumulation of carbon dioxide and other greenhouse gases in the atmosphere will probably warm the planet.
"Most of my colleagues feel that there will be some warming," said Michael Bender, a climatologist at the University of Rhode Island.
But Bender said there is still wide disagreement over the magnitude of the warming. It is this uncertainity, in part, that keeps the Bush administration from commiting to reductions in carbon dioxide. As one adminstration official who has negotiated over climate change put it: "If the temperature goes up 1 degree, who cares? If it goes up 6 degrees, everybody cares."
A U.N.-sponsored group of 300 scientists concluded last year that temperatures will probably rise 2 degrees by 2025 and 6 degrees by the end of the century. However, these predictions are based on computer simulations, which many scientists say are too crude to warrant great confidence.
Scientists are even less confident that they understand what a temperature increase will do to crops and the natural world. Many investigators believe that plants will be more vigorous in a carbon-dioxide rich world, but there is the fear that with rising temperatures, soil moisture will decrease.
"Humanity is hurtling toward a precipice," according to Michael Oppenheimer, a senior scientist at the Environmental Defense Fund. If we fail to reduce emissions, Oppenheimer and a colleague said in a book, we "are likely to alter the Earth's climate so rapidly and so thoroughly as to destroy much of the natural world and turn the world that we call civilization upside down."
Yet many others are not quite so hyperbolic.
"I just don't feel in my gut like it's a catastrophic issue," said James Angell, a climatologist with the National Oceanic and Atmospheric Administration who has been tracking worldwide temperatures with weather balloons. "My personal feeling is that we'll be able to deal with it."
"Yes, I think some warming will occur," said Peter Brewer of the Monterey Bay Aquarium Research Institute, a leader of an international project to study the response of marine algae to climate change. "But it's not a catastrophe. It's a trend we have to deal with. It's irreversible. But it will probably be subtle and spread out over decades."
The Earth's climate is so dynamic -- and the product of such a complex interplay of currents and clouds, polar ice and marine plants -- that to simulate it on a computer and predict what the future will bring is a daunting task.
Moreover, there is still tremendous uncertainty about "wild cards" in the climate, which could dampen or accelerate warming.
There is some agreement that increased temperatures will cause a slight rise in sea levels because of the way oceans expand when heated. But researchers are unsure whether even the predicted temperature increase will cause the polar icecaps to melt.
"I am supposed to be an expert on what the greenhouse effect will do to ice sheets and sea level," said Alley. "But I am only confident in one thing. I am confident that we cannot make a reliable prediction at this time about sea-level rise."
Scientists also are trying to understand if rising temperatures will lead to increased cloudiness, which could shield the planet from incoming sunlight and perhaps act to mitigate warming. Some researchers, however, have speculated that certain types of clouds may increase warming by trapping more heat.
In a perverse twist, researchers also suspect that the main ingredient in acid rain -- sulfur dioxide -- might act to seed clouds in the atmosphere and so cool the planet.