Global Stratospheric Ozone: Past, Present, and Future (Invited Presentation)

As part of the Scientific Assessment of Ozone Depletion 2018, we have been charged with the task of providing the up-to-date information regarding the state of the stratospheric ozone layer and its projected future development outside the polar regions. Two major new sources of information were available for this assessment: The LOTUS initiative on ozone profile trends in the middle and upper stratosphere and the current generation of CCMI integrations describing the long-term evolution of ozone.

The observational monitoring of ozone abundances relies on many different instruments. Numerous data records have been updated and newly merged data sets have become available in recent years. With a consolidated framework for the assessment of profile trends, LOTUS was able to provide improved uncertainty estimates for ozone trends in the middle and upper stratosphere. The results highlight regions that show indications of ozone recovery. We discuss these middle and upper stratospheric trends in the context of newly-published observations of ozone in the lower stratosphere and troposphere. We also assess the relationship between profile changes and changes in total column ozone.

A large number of comprehensive integrations with many different models was available to analyze the temporal long-term evolution of ozone (CCMI). One popular metric that has been reported for the last assessments is the so-called ozone return date to 1980 values – indicating the time horizon for when ozone in depleted regions is returning to its 1980s values. We provide updated estimates of the return dates and explain in detail the caveats associated with these dates, e.g. their strong dependence on scenario assumptions.

This strong observational and modelling basis provides a comprehensive health check of global stratospheric ozone that is presented to policy makers as part of the 2018 Assessment.