In his review of my book Science as a Contact Sport — a personal retrospective account of the development of climate science and policy covering 40 years — Roger Pielke Jr misrepresents my position on advocacy (Nature 464, 352–353; 2010).

Pielke fairly represents my decades-old argument that scientists should avoid policy prescriptions. But he omits my frequently stated context: policy advocacy by scientists is inappropriate in formal assessments, such as those of the Intergovernmental Panel on Climate Change or of the US National Academy of Sciences.

As citizens, scientists may have personal-value positions on policy. But when involved in public advocacy, they must clearly lay out their world views and separate the more objective scientific issue of risk assessment from the value-laden risk-management part. Contrary to Pielke's implication, I am aware of this 'paradox'.

Understanding science does not in itself lead to effective policy. In fact, my book demonstrates that special interest or ideological chicanery is more responsible than scientific ignorance for blocking policy. However, as Pielke notes, I did say that if people better understood what is at stake, they'd be likely to make better risk-management decisions.