FOUR SIDES TO EVERY STORY

[STEWART BRAND:] Climate talks have been going on in Copenhagen for a week now, and it appears to be a two-sided debate between alarmists and skeptics. But there are actually four different views of global warming. A taxonomy of the four:

DENIALISTS They are loud, sure and political. Their view is that climatologists and their fellow travelers are engaged in a vast conspiracy to panic the public into following an agenda that is political and pernicious. Senator James Inhofe of Oklahoma and the columnist George Will wave the banner for the hoax-callers.

"The claim that global warming is caused by manmade emissions is simply untrue and not based on sound science," Mr. Inhofe declared in a 2003 speech to the Senate about the Kyoto accord that remains emblematic of his position. "CO2 does not cause catastrophic disasters — actually it would be beneficial to our environment and our economy .... The motives for Kyoto are economic, not environmental — that is, proponents favor handicapping the American economy through carbon taxes and more regulations."

SKEPTICS This group is most interested in the limitations of climate science so far: they like to examine in detail the contradictions and shortcomings in climate data and models, and they are wary about any "consensus" in science. To the skeptics' discomfort, their arguments are frequently quoted by the denialists.

In this mode, Roger Pielke, a climate scientist at the University of Colorado, argues that the scenarios presented by the United Nations Intergovernmental Panel on Climate Change are overstated and underpredictive. Another prominent skeptic is the physicist Freeman Dyson, who wrote in 2007: "I am opposing the holy brotherhood of climate model experts and the crowd of deluded citizens who believe the numbers predicted by the computer models .... I have studied the climate models and I know what they can do. The models solve the equations of fluid dynamics, and they do a very good job of describing the fluid motions of the atmosphere and the oceans. They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests."

WARNERS These are the climatologists who see the trends in climate headed toward planetary disaster, and they blame human production of greenhouse gases as the primary culprit. Leaders in this category are the scientists James Hansen, Stephen Schneider and James Lovelock. (This is the group that most persuades me and whose views I promote.)

"If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on earth is adapted," Mr. Hansen wrote as the lead author of an influential 2008 paper, then the concentration of carbon dioxide in the atmosphere would have to be reduced from 395 parts per million to "at most 350 p.p.m."

CALAMATISTS There are many environmentalists who believe that industrial civilization has committed crimes against nature, and retribution is coming. They quote the warners in apocalyptic terms, and they view denialists as deeply evil. The technology critic Jeremy Rifkin speaks in this manner, and the writer-turned-activist Bill McKibben is a (fairly gentle) leader in this category.

In his 2006 introduction for "The End of Nature," his famed 1989 book, Mr. McKibben wrote of climate change in religious terms: "We are no longer able to think of ourselves as a species tossed about by larger forces — now we are those larger forces. Hurricanes and thunderstorms and tornadoes become not acts of God but acts of man. That was what I meant by the 'end of nature.'"

The calamatists and denialists are primarily political figures, with firm ideological loyalties, whereas the warners and skeptics are primarily scientists, guided by ever-changing evidence. That distinction between ideology and science not only helps clarify the strengths and weaknesses of the four stances, it can also be used to predict how they might respond to future climate developments.

If climate change were to suddenly reverse itself (because of some yet undiscovered mechanism of balance in our climate system), my guess is that the denialists would be triumphant, the skeptics would be skeptical this time of the apparent good news, the warners would be relieved, and the calamatists would seek out some other doom to proclaim.

If climate change keeps getting worse then I would expect denialists to grasp at stranger straws, many skeptics to become warners, the warners to start pushing geoengineering schemes like sulfur dust in the stratosphere, and the calamatists to push liberal political agendas — just as the denialists said they would.

[EDITOR'S NOTE: First published as an OpEd article in The New York Times on December 15, 2009]