• Peer-Reviewed
Elements of Change · 1994

Eliciting Expert Judgment about Uncertainty in Climate Prediction

David Keith

Senator Bill Bradley once asked a panel of atmospheric scientists at a hearing on issues of global climate change, “just what kind of surprises did you have in mind?” After the obligatory, “We cannot know a surprise in advance,” those attending admitted that they did have some inklings: radical ocean current flip-flops, permafrost melting (and possible methane release), synergisms between habitat fragmentation and species migration in response to global changes, super hurricanes, environmental refugees and attendant political instability, breakthroughs in alternative energy system prices, unexpected disease vectors, and strongly stabilizing cloud feedback effects, were some of the examples mentioned. The list is highly speculative, formidably non-linear and very interdisciplinary. Yet, such possibilities can be uttered — and other possible candidates for global change surprises were uncovered when people of achievement and insight, ranging across physical, biological, and social scientific disciplines were brought together in the congenial atmosphere of an Aspen Global Change Institute summer session. The topic of anticipating global change surprises is highly relevant as we consider how to respond to global change in the face of uncertainty. The possibility of unexpected physical, biological and social impacts of global scale environmental change is a principal uncertainty in estimating the urgency of implementing policy responses to the advent or prospect of global change. In addition to identifying and discussing a variety of candidates for global change surprises, the participants in this session worked through defining and clarifying relevant terms, and developed a typology of surprise that recognizes risk, uncertainty and ignorance. These clarifications and the typology are summarized in the following pages, as are selected candidates for global change surprises that emerged from the session.

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