Using current debates surrounding climate change as an example, this essay offers a postdisciplinary framing of the policy uses of scientific knowledge. Rather than seeing empirical knowledge as driving societal consensus, the causal arrow between science and social values should be understood as flowing in both directions. In the case of climate change, 20 years of climate science has led to few changes in public policy; but we can expect that the dire consequences of climate change, if and when they occur, will cause a rapid shift from impotent squabbling to public and political pressure to geoengineer the climate. I explore the implications of this view, and argue that geologists and society at large should learn how to make effective use of geological ignorance as well as geological knowledge.