Warming is a (95%) sure thing

WASHINGTON - Top scientists from a variety of fields say they are about as certain that global warming is a real, human-made threat as they are that cigarettes kill.

They are as sure about climate change as they are about the age of the universe. They say they are more certain about climate change than they are that vitamins make you healthy.

They'll even put a number on how certain they are about climate change. But that number isn't 100 percent. It's 95 percent.

For some nonscientists, that's not good enough.

There's a mismatch between what scientists say about how certain they are and what the general public thinks the experts mean, specialists say.

It is an issue because this week, scientists have gathered in Stockholm for a meeting of a U.N. panel on climate change, and they will probably release a report saying it is "extremely likely" - defined in footnotes as 95 percent certain - that humans are mostly to blame for temperatures that have risen since 1951.

One scientist says the panel may even boost it in some places to "virtually certain" and 99 percent.

Some climate-change deniers have looked at 95 percent and scoffed. After all, most people wouldn't get on a plane that had only a 95 percent certainty of landing safely, risk experts say.

But in science, 95 percent certainty is often considered the gold standard.

"Uncertainty is inherent in every scientific judgment," said Johns Hopkins University epidemiologist Thomas Burke. "Will the sun come up in the morning?" Scientists know the answer is yes, but they can't really say so with 100 percent certainty because there are so many factors out there that are not quite understood or under control.

George Gray, director of the Center for Risk Science and Public Health at George Washington University, said that demanding absolute proof doesn't make sense.

"There's a group of people who seem to think that when scientists say they are uncertain, we shouldn't do anything," said Gray, who was chief scientist for the Environmental Protection Agency during the George W. Bush administration. "That's crazy. We're uncertain and we buy insurance."

With the U.N. panel about to weigh in on the effects of greenhouse-gas emissions from the burning of oil, coal and gas, the Associated Press asked scientists who specialize in climate, physics, epidemiology, public health, statistics, and risk just what in science is more certain than human-caused climate change, what is about the same, and what is less.

They said gravity is a good example of something more certain.

The president of the National Academy of Sciences, Ralph Cicerone, and more than a dozen other scientists contacted by the AP said the 95 percent certainty regarding climate change was most similar to the confidence scientists have in the years' worth of evidence that cigarettes are deadly.

Even the best study can be faulted because nothing is perfect, and that's the strategy of tobacco defenders and climate deniers, said Stanton Glantz, a medicine professor at the University of California, San Francisco and head of its tobacco control research center.