Polar Bear Population Forecasts: A Public-Policy Forecasting Audit

By | December 17, 2007

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Calls to list polar bears as a threatened species under the U.S. Edangered Species Act are based on forecasts of substantial long-term declines in their population. Nine government reports were prepared to support the listing decision. We assessed these reports in light of evidence-based (scientific) forecasting principles. None referred to works on scientific forecasting methodology. Of the nine, Amstrup, Marcot and Douglas (2007) and Hunter et al. (2007) were the most relevant to the listing decision. Their forecasts were products of complex sets of assumptions. The first in both cases was the erroneous assumption that General Circulation Models provide valid forecasts of summer sea ice in the regions inhabited by polar bears. We nevertheless audited their conditional forecasts of what would happen to the polar bear population assuming, as the authors did, that the extent of summer sea ice would decrease substantially over the coming decades. We found that Amstrup et al. properly applied only 15% of relevant forecasting principles and Hunter et al. only 10%. We believe that their forecasts are unscientific and should therefore be of no consequence to decision makers. We recommend that all relevant principles be properly applied when important public policy decisions depend on accurate forecasts.