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Can we be certain of uncertainty?

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Despite notions to the contrary, scientists and laypeople have something in common: dealing with uncertainty.

Scientists typically treat uncertainty objectively. Just as we know that flipping a coin can produce two equally likely outcomes, most scientific unknowns are approached as a set of possible outcomes with corresponding probabilities.

Individual members of society tend to have a more subjective, intuitive sense for uncertainty. We immunize our children because it lessens risk, not because we know the exact probability that they will contract a disease.

Accepting uncertainty is all about living despite a lack of total knowledge.

Although humans do this naturally, uncertainty can be difficult to conceptualize.

"Uncertainty and controversy are turn-offs for the public," said Susanne Moser, a communications specialist at the National Center for Atmospheric Research. "People just don't want to think about it."

The misunderstanding of unknowns can cause inaction, indifference and ignorance of issues directly relevant to the public interest.

There is perhaps no better example of this effect than society's response to climate change. Although the Intergovernmental Panel on Climate Change says that the warming of the climate system is unequivocal and will continue, there is uncertainty associated with how much the Earth will warm as emissions of greenhouse gases rise.

While some have said scientists need to reduce that uncertainty significantly before society acts to mitigate global warming, two UW scientists have demonstrated that how much the Earth will warm is an uncertainty by nature.

Gerard Roe, a professor of earth and space sciences at the UW, and Marcia Baker, professor emeritus of atmospheric sciences, published a paper in the journal Science illustrating the uncertainty inherent in predicting climate change.

"Decreasing uncertainty associated with the physical processes underlying the climate system does not produce a proportional decrease in the uncertainty of future warming," Roe said. "Sensitive systems are inherently uncertain."

Accepting that the warming we can expect will come with some fundamental uncertainty has strong implications for our approach to reducing greenhouse gas emissions.

"If the Federal Reserve Bank said, 'We know economics; we're going to change interest rates every two years,' we'd think they were crazy," Roe said. "Instead, they change rates more often than that. As new information becomes available, adjustments are made."

Similarly, Roe said that a second look at how society responds to global warming may be in order. Instead of fixing specific carbon dioxide concentrations to aim for in the future, he and others suggest that society should adopt flexible policies capable of changing in response to new information on the rate of warming.

Rather than recoil in the face of uncertainty, society should follow the lead of individuals, embracing it as an essential part of life. That requires an honest and continuous assessment of the risks we face and the responses we can undertake. Even if sound policies are put in place, the challenge of motivating people to think and act differently lies on the horizon.

As Roe put it: "Human nature is a bigger problem than mother nature."

[Reach reporter Brian Smoliak at]

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