William Ball, researcher at ETH Zürich.
William Ball, researcher at ETH Zürich.


William Ball
Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland


Evidence for continued ozone layer reduction


Stratospheric ozone protects life from harmful ultraviolet radiation. The Montreal Protocol, enacted to prevent ozone depletion from human activity, halted declines in column-integrated ozone in the 1990s; the upper stratosphere is recovering, but lower stratospheric trends are unknown. 

To accurately estimate decadal trends in stratospheric ozone requires combining observations from multiple instruments. However, trends between composites disagree due to data-artefacts that remain after merging data together. We developed a new methodology to account for the artefacts using only the data itself in addition to prior knowledge about ozone variability and known problems during instrument operation. Furthermore, we use dynamical linear modelling (DLM), a Bayesian multiple linear regression, to estimate robust trends. 

As a result of building confidence in the data, we find clear evidence that lower stratospheric ozone continues to decline, preventing total ozone recovery. This result contradicts expectations and, with no clear understanding of why this trend has emerged, implies that the problem of ozone depletion is not yet fully resolved. The decline may have an impact future estimates of ozone layer recovery and future surface levels of ultraviolet radiation

The seminar will be on the topic of the article Evidence for a continuous decline in lower stratospheric ozone offsetting total ozone recovery.


Time and Place

Tuesday May 8th, 11.15
Rossbysalen C609, Arrhenius Laboratory, 6th floor