Global warming: a few skeptics still ask why it's happening

With alarms bells over global warming ringing ever louder and more insistent, is it possible – or credible – for an active scientist working on climate questions to be skeptical of the cause or future severity?

Amid mounting evidence that temperatures are rising on planet Earth, the "skeptics" and "agnostics" are a smaller band than they used to be. Yet those who do still harbor doubts about a looming global-warming crisis are quietly continuing to test alternative ideas about how climate works and what, if not the burning of fossil fuels, might be causing the temperature creep.

This week some of the doubters testified at a Senate hearing on global warming, perhaps their last chance to take the bully pulpit for at least two years, now that Congress is shifting to Democratic control. At a hearing chaired by Sen. James Inhofe (R) of Oklahoma, who has dismissed warnings of a global-warming crisis as a hoax, they expressed misgivings about the reliability of climate forecasts and questioned whether the current warming even is unusual, among other things.

These objections are not new, and many environmentalists and scientists say research has already passed them by. Moreover, they distract from the urgent need to get on with curbing emissions of carbon dioxide and other greenhouse gases.

Yet even critics acknowledge that science is a discipline that needs its maverick thinkers – and that the global-warming skeptics and their research provide a kind of reality check on the climatology field. They acknowledge, too, that scientific training, temperament, and field of specialty factor into the motivations of researchers who retain reservations about human-induced climate change.

"To imply that any scientist who has questions about global warming is somehow part of an orchestrated campaign" by industry or interest groups greatly oversimplifies the spectrum of motivations among those outside the consensus view, says Annie Petsonk, a lawyer with Environmental Defense. "It is much more complicated than that."

History shows that science is a field in which it can be difficult to achieve consensus – even when the question at hand has no public-policy implications. When the question gets tangled up with politics, economics, and lifestyles, the ranks of the unconvinced can thin far more grudgingly.

"Science moves slowly," says John Wallace, an atmospheric scientist at the University of Washington who used to be skeptical about human-induced warming. He cites the controversy over smoking and health as an example of skepticism's durability when public policy is involved. Even after accounting for the influence of the tobacco lobby, "there were scientifically very conservative people who maintained ... doubt until very late in the game – much to the detriment of a lot of smokers," he says. They insisted, he says, on absolute certainty on the link between smoking and health.

Not all remaining skeptics fit neatly into one pigeonhole. They do agree that the climate has warmed and that humans have pumped more heat-trapping gases into the atmosphere. But some hold that the climate is too complex to reliably forecast its future trends. Other suggest that natural fluctuations in climate remain the main drivers of warming. Still others say that, on balance, warming will be good for humanity.

Within those broad groups, there's overlap and even ambivalence.

"There are days when I am involved in research and I would look to anyone like: This guy's completely on board," says Robert Balling Jr., an atmospheric scientist at Arizona State University who is often is identified as a a skeptic. "Other days, I might be involved in a project that could be seen on the skeptical side. I don't understand how someone working in this field for 15 years can publish nothing" but work supporting the consensus view "and not be a little skeptical."

Some who look at the climate issue through the lens of geological time hold that warming's impact on society pales in comparison with the sudden, natural swings in climate that can occur. The triggers are unknown, and society is woefully unprepared for them, says Australian researcher Robert Carter, one of the testifiers before the Senate Environment and Public Works Committee on Wednesday. The global-warming debate, he argued, is a distraction that keeps people from focusing on what he sees as this greater threat.

The University of Oklahoma's David Deming went further, arguing for a form of geo-engineering to forestall the next ice age. In a phone interview, Dr. Deming said too little is known about how the climate system works to overhaul economies in an effort to affect it. He cites the mechanisms that cause ice ages as an example. And he points to work by Richard Muller, a physicist at the University of California at Berkeley who has suggested an unusual cosmic source for cooling cycles that occur roughly every 100,000 years.

But in an interview, Dr. Muller chuckles and notes that measurements he hoped would bolster his case for periodic swings through a patch of cosmic dust as the culprit so far failed to turn up evidence of dust.

He does have misgivings about computer modeling as a forecast tool and about uncertainties in climate-change science. But given the current state of the science, "we can't rule out that a substantial portion of the warming is due to human influence," he says. "And we have a plausible mechanism that can account for the changes. If we extrapolate those forward, the effects would be bad for the US," even if Canada and Russia might like a warmer climate.