Robert W. Adler
Gov. Gary Herbert and several Utah legislators argue that the costs of addressing global warming are so great that we should not act absent conclusive proof of human responsibility. They cite a few scientists who dissent from the vast majority of scientists studying the issue.

The governor and his legislative colleagues are correct that skeptics can play an important role in scientific inquiry, and those critics' voices should never be stifled.

But insistence that mitigation await conclusive evidence, which can be stymied so long as even a few scientists disagree, sets an impossible burden of proof that we never apply to similar public decisions in the face of scientific uncertainty.

Science is inherently fraught with uncertainty, and a standard of conclusive proof guarantees policy paralysis.
The argument that steps to address global warming require conclusive scientific proof is based on the deceptively appealing but flawed logic that the costs of controls could be so large and the resulting economic impacts so severe that they are not justified until we know we are correct.

Decisions about how to act in the face of uncertainty, however, should consider three factors: the cost of taking action, the likelihood of harm and the cost of not acting if the risk turns out to be real.

The "conclusive proof" standard considers the first two but not the third issue, in this case the potentially catastrophic economic, human and environmental costs of global warming if the majority scientific view is correct. 

As Judge Skelly Wright wrote in a seminal case on environmental risk: "[d]anger ... is not set by a fixed probability of harm ... public health may properly be found endangered both by a lesser risk of greater harm and by a greater risk of a lesser harm."

If evidence suggests a 50% probability of harm, prudent risk managers invest in prevention if the cost of doing so is less than the cost of the harm.

Deciding not to act because you may be wrong ignores the equal probability that the harm will occur and cause even higher costs. As the consequences of harm increase compared to the cost of prevention, a lower showing of risk is warranted, not a standard that approaches 100% certainty.

We never require "conclusive proof" in the face of other serious but uncertain risks. The United States spends trillions of dollars to defend against nuclear and other military threats that may never materialize, because the costs of not acting might be catastrophic.

Utah spent millions of dollars to upgrade the State Capitol and other public buildings to withstand earthquakes that may never occur within the lifespans of those structures. They did so because of potential loss of life or serious injury if an earthquake occurs. Politicians oppose imported nuclear wastes where risks of accidents are low but consequences high.

Under Herbert's "conclusive evidence" standard, we should take no action until the risk of global warming is virtually 100%, even though the cost of being wrong is potentially unequaled in human experience, rivaled only by the possibility of nuclear war. But the longer we wait, the more greenhouse gases accumulate in the atmosphere, the more serious the impacts are likely to be, the longer it will take to reduce them and the higher response costs will be compared to acting now.

Scientific debate about global warming is healthy. Setting an unreasonable standard of proof before acting is a potentially catastrophic mistake.
Robert Adler is the James I. Farr Chair and Professor at the University of Utah's S.J. Quinney College of Law.