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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.

Ultraviolet B radiation (UVBR, 280–320 nm), the most biologically damaging portion of the solar spectra reaching the Earth’s ground, received considerable scientific attention after the discovery of the spring stratospheric ‘ozone hole’ formation in the late 1970s over Antarctica. Recently, similar low ozone conditions were observed over the Arctic and occasionally at lower latitudes. Furthermore, expected ocean acidification, increased surface water temperatures, and modifications in the structure of the water column due to global change expanded the concerns regarding the potential damage of global change to the structure of marine food webs. This chapter reviews the effects of UVBR on various marine ecosystems. Introduction of the chapter gives a description of factors that influence the UVBR intensities that reach these ecosystems such as latitude, season, stratospheric ozone layer thickness, and penetration within the water column. Then, the chapter depicts the effects of UVBR on the food webs of some important marine ecosystems, such as polar oceans, coastal waters, fronts and upwellings, oceanic gyres, and benthic ecosystems including coral reefs. Finally, this chapter investigates the potential interactions of enhanced UVBR along with other climate change stressors such as global warming and ocean acidification.

In this conversation, Nobel Prize winner Mario J. Molina reflects on the ethical side of science. He explains how several decades ago, together with the scientist F. Sherwood Rowland, he predicted that human activity was endangering the ozone layer. They discovered the mechanisms which could bring about the destruction of the layer due to the continuous release of industrial compounds, such as the so-called chlorofluorocarbons (CFCs), into the atmosphere. Professor Molina relates how the issue with the ozone layer was the first example of a problem on a truly global scale for science and, as such, had to be tackled, because without the ozone layer, life on our planet would not have evolved as we know it. Education and training are proving a great help with how the present challenge of stopping or mitigating the daunting problem of global warming should be approached. In the dialogue, different courses of action for persuading both decision-makers and the public are proposed. It is however proving rather difficult to achieve and something which, according to Professor Molina, is also related to education.