Earth's Fidgeting Climate

"I think from the viewpoint of thoughtful scientists, there's not going to be any single indicator, but rather there's going to be a concurrency of lots of indicators that's going to be convincing," said Dr. Tony Rosenbaum, a professor at the University of Florida who specializes in the politics of environmental issues.

Showing how greenhouse gases are trapped in the atmosphere

While the "big picture" view of all the evidence from research around the world may offer scientists their best chance to understand global warming, no mathematical tools exist for combining all the data into a definitive, objective conclusion. Scientists' only option is to weigh the evidence and make a professional judgment.

"There is a dichotomy between what is realistic and achievable, and what some people would like to hold as the ideal proof," Mosley-Thompson said.

"I don't think this discussion lends itself to standard statistical testing," she continued. "Certainly you can test, statistically, the output of one climate model against another, a climate model against observation, an ice core data against observation -- but those are snippets .... What does it mean for reality? There's where the translation becomes difficult."

When drawing a conclusion from the mosaic of evidence, different scientists will use different criteria, Crowley said.

"I think that there are many scientists that are still locked into the idea that we have to prove something (about causes of climate change) beyond a reasonable doubt," Crowley said. "I don't think we necessarily have to do that. ... In a court of law you can convict based on a weight of evidence. ... That's the way you approach this type of problem."

Because such conclusions are based on a scientist's professional judgment, disagreement is inevitable.

"There is enormous room for differences of opinion among equally competent scientists of good will," Rosenbaum concluded.

"There are always people -- and reasonable people -- who fall on both sides of the argument," agreed Abdalati. "And there are reasons for that. So the best we can hope for is a consensus."

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