Risks to the stratospheric ozone shield in the Anthropocene
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PERSPECTIVE
Risks to the stratospheric ozone shield in the Anthropocene This article belongs to Ambio’s 50th Anniversary Collection. Theme: Ozone Layer Susan Solomon
Received: 13 August 2020 / Revised: 20 October 2020 / Accepted: 24 October 2020 / Published online: 21 November 2020
Abstract Crutzen (1974) and Crutzen and Ehhalt (1977) presented two key papers in Ambio that in Ambioexemplify how science first revealed to humankind the potential for damage to our ozone shield in the Anthropocene. Crutzen’s (1974) review is a sweeping summary of the risks to the ozone layer from supersonic aircraft, chlorofluorocarbons, as well as nuclear weapons testing and nuclear war. Crutzen and Ehhalt (1977) described how the nitrous oxide produced from fertilizers could pose another threat to the stability of the stratospheric ozone layer. The two papers are part of a body of influential scientific work that led to the pioneering Montreal Protocol to Protect the Earth’s Ozone Layer to phase out production of chlorofluorocarbons (in 1987), as well as national decisions that slowed or stopped production of supersonic planes (in the 1970s). They remain guideposts today for ongoing international negotiations regarding reducing emissions from fertilizer and limiting nuclear testing. Keywords Chlorofluorocarbons Fertilizers Montreal Protocol Nuclear Ozone Policy
demonstrating that the stratospheric ozone layer (the Earth’s protective shield against damaging ultraviolet sunlight) was at risk due to human activities. Ehhalt is best known for critical measurements that provided an early bedrock database for stratospheric trace species that affect the ozone layer, including nitrous oxide and chlorofluorocarbons. Together they analyzed the sensitivities of the ozone layer to human activities involving nitrous oxide increases from human use of fertilizer in a landmark paper (Crutzen and Ehhalt 1977). Humans have taken action to protect the ozone layer, guided in part by this scientific information. Protection of the ozone layer against chlorofluorochemicals (chlorofluorocarbons, or CFCs) is widely considered the signature environmental success story of the twentieth century. But the story has not yet ended. Policy discussions continue today regarding whether and by how much fertilizer-related emissions of nitrous oxide (N2O) could be and should be constrained because of impacts on both the ozone layer and the climate system. Below I briefly discuss the remarkable history of these two papers, the ozone protection policies that flowed from them, and the unfinished business of N2O emission.
INTRODUCTION The 1970s witnessed an explosion of scientific understanding of stratospheric ozone that rocked both the scientific and political spheres, and continues even to the present day. A few key scientific leaders and their papers initiated this remarkable period of scholarly advancement and societal response to scientific information. Among the foremost are Paul Crutzen and Dieter Ehhalt, in papers published in Ambio. In a tour-de-force
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