Assessing Extreme Outcomes: The Strategic Treatment of Low Probability Impacts of Climate Change

Many assessments of climate change fail to consider the possibility of low probability, yet catastrophic, outcomes of greenhouse warming. A noteworthy example is the potential rapid deterioration of the West Antarctic ice sheet. If the ice sheet were to melt, as a minority of scientists believe it may, sea levels could rise by five meters or more in the next century. This study seeks to develop a theory that can predict why certain classes of assessments assess extreme outcomes, while other classes of assessments ignore them. Work in behavioral psychology argues that individual decision-makers display predictable bias when interpreting low probability events, either underestimating or overestimating the associated risks. Drawing on this work, this study theorizes that assessors who operate by consensus, and who are trying not to create controversy, will avoid issue areas, such as low probability outcomes, where biased interpretations are likely. Staff advisors who are asked to assess such issue areas will seek to offer explanations that overcome people's propensity for bias. Finally, advocates writing assessments will seek to take advantage of people's bias. Using a case study of the West Antarctic ice sheet issue, this study finds empirical evidence that supports these predictions.