Source: What 95% Certainty of Warming Means to Scientists, By Seth Borenstein AP Science Writer, September 24, 2013. abcnews.go.com
Notes: Friday, September 27, 2013, United Nations Intergovernmental Panel on Climate Change (IPCC) released its fifth assessment report. It states it is "extremely likely" — which they define in footnotes as 95 percent certain — that humans mostly caused global temperatures to climb since 1951.
Many climate-change contrarians look at 95 percent and scoff. After all, risk experts say most people wouldn't get on a plane that had only a 95 percent certainty of landing safely.
However as Seth Borenstein writes, "in science, 95 percent certainty is often considered the gold standard for certainty."
"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, says demanding absolute proof on things like climate change makes no 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 U.S. Environmental Protection Agency during the George W. Bush administration. "That's crazy. We're uncertain and we buy insurance."
Borenstein and the AP contacted Ralph Cicerone, President of The National Academy of Sciences, and more than a dozen other scientists for this article. They see the 95 percent climate change certainty is most similar to the confidence scientists have in the decades' worth of evidence that cigarettes are deadly.
One IPCC climate scientist interviewed by Borenstein said the panel even thought about boosting some places to "virtually certain" and 99 percent.
For instance, Jeff Severinghaus, a geoscientist at the Scripps Institution of Oceanography, stated that through the use of radioactive isotopes, scientists are more than 99 percent sure that much of the carbon in the air has human fingerprints on it. Even more, because of basic physics, scientists are 99 percent certain that carbon traps heat in what is called the greenhouse effect.
However, the role of nature and lots of other factors bring the number down to 95 percent when you want to say that the majority of the warming is human-caused, he said.
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