"By definition, uncertainties abound in our work; there's nothing to be done about that," writes David Michaels about scientists studying epidemiology and climate change. Michaels is a professor at George Washington University School of Public Health, working on occupational disease, and served as an assistant secretary of Energy between 1998 and 2001. "Our public health and environmental protection programs will not be effective if absolute proof is required before we act. The best available evidence must be sufficient. Otherwise, we'll sit on our hands and do nothing. Of course, this is often exactly what industry wants. That's why it has mastered the art of manufacturing uncertainty, of demanding often impossible proof over common-sense precaution in the realm of public health."