Science is never finished, so the relevant policy question is always whether the available evidence is persuasive, and whether the established facts outweigh the residual uncertainties. This is a judgment call. Chris Bernabo, who worked at the White House Council on Environmental Quality at the time and served as research director for the Interagency Task Force on Acid Precipitation, suggests that because so much more was at stake for Canada —70 percent of their economy at the time came from forests and fish or tourism related to them—it was only natural that they would interpret the evidence as more dire than their U.S. counterparts would. Pollution went across the border in both directions, but by far the larger share came from the United States, which would therefore bear most of the burden of cleanup. As Bernabo puts it, for any problem, the degree of scientific certainty demanded is proportional to the cost of doing something about it. So the United States was more resistant to accepting the evidence and demanded a high level of certainty.