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Discerning ExpertsThe Practices of Scientific Assessment for Environmental Policy$
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Michael Oppenheimer, Naomi Oreskes, Dale Jamieson, Keynyn Brysse, Jessica O'Reilly, Matthew Shindell, and Milena Wazeck

Print publication date: 2019

Print ISBN-13: 9780226601960

Published to Chicago Scholarship Online: September 2019

DOI: 10.7208/chicago/9780226602158.001.0001

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Assessing Ozone Depletion

Assessing Ozone Depletion

(p.81) Chapter Three Assessing Ozone Depletion
Discerning Experts

Michael Oppenheimer

Naomi Oreskes

Dale Jamieson

Keynyn Brysse

Jessica O’Reilly

Matthew Shindell

Milena Wazeck

University of Chicago Press

International assessments of ozone depletion began in the 1980s, after anti-regulation groups (such as the CFC industry) seized on differences between early national and institutional assessments, and the policy leanings expressed in some of them, as justification to delay regulation of CFCs. This spurred Bob Watson and colleagues to bring together scientists of varying nationalities, disciplines, and interests to produce large international ozone assessments, with the explicit goal of being seen as authoritative, credible, objective, and policy-relevant but not policy-prescriptive. These scientists focused on producing brief, accessible executive summaries, replete with neutrally phrased if–then statements, thought to appeal to busy politicians. These assessments are widely regarded as very successful, most importantly for having contributed to the Montreal Protocol. However, when unexpected seasonally and geographically localized ozone depletion was detected over Antarctica (the Ozone Hole), assessors faced huge uncertainty and insufficient understanding of heterogeneous chemistry, which had formerly been dismissed as unimportant. In response they produced new knowledge by repurposing ozone metrics such as chlorine loading potential to predict future ozone levels in the absence of adequate models. The assessment of ozone depletion illustrates how an assessment may be highly successful even while grappling with highly uncertain scientific knowledge.

Keywords:   heterogeneous reactions, ozone depletion, ozone hole, Montreal Protocol, Bob Watson

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