In this video, Dr Angela Benedetti highlights the importance of past and current stratospheric ozone observations, and explores the key role that Earth observation played in delivering the Montreal Protocol and in monitoring its effectiveness.

Stratospheric ozone acts like a protective blanket located high in the atmosphere, shielding life on Earth from harmful ultraviolet (UV) radiation coming from the Sun. In the 1980’s scientists observed that this important layer was slowly depleting due to the excessive use of long-lived manmade chemicals called chlorofluorocarbons (CFCs). As the released CFCs circulated into the stratosphere, a process that can take a few years to occur, they broke down and produced highly reactive chlorine atoms. Each chlorine atom can break apart more than 100,000 ozone molecules, so the stratospheric ozone layer was rapidly being destroyed, along with its ability to block out UV rays.

Earth observation data played a pivotal role in the events leading up to the signing of the Montreal Protocol in 1987, helping to ban the production and use of CFCs and forcing their replacement with other chemicals. Observations from satellite instruments provided powerful and compelling information that confirmed initial observations of ozone depletion made by balloons, and then alerted scientists, and later the public, that this process was occurring above huge areas over Antarctica. The issue was soon recognised worldwide as an extremely serious environmental threat. Since the ratification of the treaty, satellites continue to provide key observations of the state of the ozone hole, allowing us to monitor its recovery.

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• Dr Angela Benedetti

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