S P A R C Stratospheric Processes And their Role in Climate A project of the World Climate Research Programme Home Initiatives Organisation Publications Meetings Acronyms and Abbreviations Useful Links

The Earth’s Protective Ozone Layer still Remains Vulnerable

Report on the Quadrennial Symposium on Atmpospheric Ozone

Kos, Greece. 1-8 June 2004

Cristos S. Zerefos, University of Athens, Greece (zerefos@geol.uoa.gr)

The XX Quadrennial Symposium on Atmospheric Ozone coincided with the 20th anniversary of the discovery of the springtime Antarctic ozone hole. It also marked two decades of intensified atmospheric monitoring globally and basic research in atmospheric chemistry and physics. The progress in our understanding of the impact of human activities on the chemistry and physics of the global stratosphere since the previous Quadrennial Ozone Symposium was presented among the 690 research papers at the XX Quadrennial Ozone Symposium, held in Kos, Greece, 1-8 June 2004 and attended by 450 scientists from 60 countries. The papers presented and the proceedings of the Symposium can be found at www.QOS2004.gr.

Among the important topics discussed at the Symposium were recent research on possible ozone recovery, results from an expanded network of satellites and ground-based stations, ozone-climate interactions, modeling and chemistry, results from monitoring of the global composition of the troposphere from satellites and measurements of UV-B solar radiation reaching ground level, among others.

Evidence was presented that ozone in the past few years is a little higher than we expect from earlier projections based on sensitivity of ozone to influences of aerosols, halogen compounds and the solar cycle. There may be the beginning of a recovery in the data, an issue that it was shown to be complicated by a number of factors among which prominent role is played by changes in meteorology, greenhouse gases and in the radiation balance, not excluding the observed recovery of the ozone layer from its perturbation by the Pinatubo volcanic eruption in the early 90s. The evaluation of future ozone recovery in a changing climate and the effect of ozone on that climate has shown the importance of feedback mechanisms between water vapour content in a warmer planet.

The need for the continuation of well-calibrated instruments and measurements was discussed extensively, and emphasis was given to the use of satellite and ground-based data (e.g. NDSC and the Global Ozone Observing System) to evaluate models and ozone loss and its expected recovery.

Numerous chemistry/climate models were presented at the conference. They addressed the problem of how changes in the meteorology or climate interact with changes in the chemistry of ozone. One problem is how changes in meteorology over the last 25 years may have contributed to observed ozone changes and feedback mechanisms. Models can then be used to extrapolate that knowledge to what may happen in the future with the expected increase in methane, nitrous oxide, and carbon dioxide.

Significant new work that combines satellite and in situ observations with model calculations was presented at the Symposium providing an insight into the budget of oxides of nitrogen and a range of halogen species, which are indispensable to our understanding of the global carbon and hydrological cycles. Water vapour presents a particularly important challenge. Satellite data, shown at the meeting, is not consistent in trend with previous ground-based data. Understanding the feedback mechanism between water vapour content, ozone, and polar stratospheric clouds is critical to the evaluation of predictions of ozone in a future warmer global atmosphere.

Important progress was made in monitoring the tropospheric ozone budget with the development of new observational techniques from satellites, combined with models of the tropospheric composition. It turns out that the key factors influencing the tropospheric ozone budget (precursors, long-range transport in the troposphere and intrusions from the stratosphere) make the determination and attribution of tropospheric ozone trends difficult.

Long-range transport of tropospheric pollution and its coupling to climate was targeted in a number of studies using climate/chemistry models. Other studies have shown the importance of long-range transport of pollutants to maintain regionally high back ground levels of tropospheric ozone. For example, NASA’s satellites and balloons reveal that seasonal episodes of high ozone over south Atlantic begin with pollution sources originating thousands of miles away.

Future UV-B levels for 2000-2019 are predicted to decrease for all seasons but the trends are typically not statistically significant, except during spring over both hemispheres. UV-B trends are mainly caused by the total ozone trends because in the future cloud changes are predicted to be small in the coupled chemistry climate model used in these results. Nonetheless, there is a region over western Europe which is predicted to show an increase in UV-B due primarily to a decrease in cloudiness. The complexity of interference of cloud and other physical parameters in influencing UV-B level at ground level was targeted in several papers.

The main conclusion drawn from the individual oral and poster presentations of the Symposium, the main conclusion is that the detection of ozone recovery still requires patience. We have still a long way to go to understand the complex system of interactions between ozone and a globally changing environment and the best tools we have at present are the continuation of global quality observations both from ground and from space. UV-B levels in the coming decade or so are predicted to decrease for all seasons except during spring over high latitudes of both hemispheres.

Acknowledgements

The author is indebted to P.J. Crutzen, Rich Stolarski, Ivar Isaksen, Sophie Godin, Hennie Kelder, Andy Matthews, Tom McElroy and several of the conveners of the Symposium for fruitful discussions on the outcome of the Symposium.

TOP