Evidence for the effectiveness of the Montreal Protocol to protect the ozone layer

J A Mäder,W A Stahel,H E Rieder,J Staehelin,T Peter,D Brunner

doi:10.5194/acp-10-12161-2010

Abstract

Abstract. The release of man-made ozone depleting substances (ODS, including chlorofluorocarbons and halons) into the atmosphere has led to a near-linear increase in stratospheric halogen loading since the early 1970s, which levelled off after the mid-1990s and then started to decline, in response to the ban of many ODS by the Montreal Protocol (1987). We developed a multiple linear regression model to test whether this already had a measurable effect on total ozone values observed by the global network of ground-based instruments. The model includes explanatory variables describing the influence of various modes of dynamical variability and of volcanic eruptions. In order to describe the anthropogenic influence a first version of the model contains a linear trend (LT) term, whereas a second version contains a term describing the evolution of Equivalent Effective Stratospheric Chlorine (EESC). By comparing the explained variance of these two model versions we evaluated, which of the two terms better describes the observed ozone evolution. For a significant majority of the stations, the EESC proxy fits the long term ozone evolution better than the linear trend term. Therefore, we conclude that the Montreal Protocol has started to show measurable effects on the ozone layer about twenty years after it became legally binding.

Highlights

Stratospheric ozone depletion by chlorine radicals was first discussed by Stolarski and Cicerone (1974) and Molina and Rowland (1974)
The potential vorticity (PV) over a station at different potential temperature levels is mapped to the latitude, which encloses the same area as the PV contour
It is known that changes in atmospheric dynamics contributed significantly to the past evolution of stratospheric ozone at different sites (e.g. Labitzke and van Loon, 1999; Chipperfield and Jones 1999; Appenzeller et al, 2000; Hadjinicolaou et al, 2002; Orsolini and Doblas-Reyes, 2003; Harris et al, 2008) and that the increase in total ozone found at northern mid-latitudes in the 1990s (Hood and Soukharev, 2005; Harris et al, 2008) is attributable to a large extent to changes in dynamics

Summary

Introduction

Stratospheric ozone depletion by chlorine radicals was first discussed by Stolarski and Cicerone (1974) and Molina and Rowland (1974). An efficient reduction of the global anthropogenic emissions of ODS was reached by the Montreal Protocol (1987) and its subsequent Amendments (WMO, 2007) This was confirmed by long-term measurements of selected CFCs at remote ground stations (Montzka et al, 1996) as well as by balloon-borne measurements in the stratosphere (Engel et al, 2002). Results of numerical simulations published by Hegglin and Shepherd (2009) predicted remarkable differences in the evolution of the ozone layer in the Northern and the Southern Hemisphere within the current century. Their results show that column ozone is expected to increase in the Northern Hemisphere all the way to the pole, while for the Southern

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