1 Assessment of the Stratospheric Ozone Layer: Past and Future (Karma of and Nirvana for O 3 ) A.R. (Ravi) Ravishankara NOAA, Earth System Research Laboratory Chemical Sciences Division 1.What were the major findings from the 2006/2007 assessment 2.Where were some of the big issues/uncertainties 3.My personal take on what are likely to be the big issues in the next assessment and beyond No discussion of organizational issues in this talk - a little premature Color code: Black or red- What the assessment said Blue- What I think (possibly wrongly!)

2 Updating the Ozone Assessment Science Assessment of Ozone Depletion: 2006 Cochairs Ayité-Lô Ajavon (Togo) Daniel L. Albritton (USA) Robert T. Watson (USA) Scientific Steering Committee Marie-Lise Chanin, CNRS, France Susana Diaz, CAIC, Argentina John Pyle, University of Cambridge, UK Theodore Shepherd, University of Toronto, Canada A. R. Ravishankara, NOAA, USA Many of you contributed directly and all contributed indirectly

3 The 2006 Science Assessment Incremental, but significant, changes/updates The Parties took some key action in Montreal based on this assessment - HCFCs will be phased out sooner The coupling to climate is a major issue

4 The Preparation of the 2006 Science Assessment, con’t The Terms of Reference from the Parties (Decision XV/53): Assess the state of the ozone layer and its expected recovery Discuss recent occurrences of the Antarctic ozone hole Evaluate trends in ozone-depleting substances (ODSs) Analyze the role of atmospheric bromine in ozone depletion Assess the impacts of climate change on the ozone layer’s recovery Discuss past trends and future expectations for global ozone, polar ozone, and surface ultraviolet radiation Questions for the “accountability” phase of the Montreal Protocol

5 The Major Findings and Conclusions of the 2006 Science Assessment The Montreal Protocol is working! (Ozone improving? Influence on UV, climate, etc.?) 1980 Now ~ 2100 ODS production ODS in the atmosphere Ozone levels – measured and predicted UV levels – measured and predicted ODS production Ozone-depleting chlorine and bromine in the stratosphere Global ozone change Ultraviolet radiation change (a) (b) (c) (d) Work of many as viewed from way up there…

6 HCFCs will continue to contribute to ozone depletion until roughly the middle of the 21st century. (Impact of last week’s decision in Montreal?!) Release of “banked” CFCs (and Halons) will also contribute. ODS production 1980 Now ~ 2100 HCFCs – less efficient than CFCs, but still destroys ozone CFCs are still produced by Article 5 countries CFCs chlorofluorocarbons hydrochlorofluorocarbons Issues of Production of Ozone-Depleting Substances Can the productions be translated to emissions and emissions to atmospheric abundances? Reporting of emissions/production in the past and in the future… This is what the countries (people) care about a lot… Important Issue!

7 ODS decreasing in the lower atmosphere (where they are emitted) as well as in the stratosphere where the ozone layer is MP is working as intended in terms decreases in ODSs ODS Changes in the lower atmosphere ODS Changes in the stratosphere Trends of Ozone-Depleting Substances in the Atmosphere

8 Trends of Ozone-Depleting Chemicals in the Atmosphere: The Future Combined effective abundances of ozone-depleting chlorine and bromine in the stratosphere. Uncertainties in transport, banks, and future emissions lead to uncertainties in future levels. Failure to continue compliance with the MP could delay, or even prevent, the ozone layer recovery Now ~ 2100 Ozone-depleting chlorine and bromine in the stratosphere

9 How does the EESC change with time? - Chlorine-bromine mix? Future emissions? - Transport (climate change?) Dealing with Lifetime issues - Age of air issues: in the past, now and the future Short-lived species have contributed a lot to current decline… - Transport of the short-lived and very short-lived species species (t < a couple of weeks, e.g., CF 3 I) are important… Concept and quantification of “lifetime” -For both long-lived and short-lived gases - Implication to metrics! (ODP, GWP) Issues about Trends of Ozone-Depleting Chemicals in the Atmosphere

10 Global Ozone Observations  There are early signs that the ozone layer is starting its expected recovery.  A clear statement on recovery would “require” having a clear temporal trend in ozone AND Attribution of changes to all contributors… Coupling and non-linearity… 2010 ?

11 Polar Ozone Changes Polar O 3 loss remains large and highly variable, as measured by many metrics. The annual variations are expected in the next decades. Variations in the ozone hole during this and next decade are mostly due to meteorology – ozone hole in 2002 and 2006 are not “anomalous.” The duration of the ozone hole will change the extent of “ozone hole” & Arctic ozone depletion in the future. Impact of climate change and compositional change on ozone hole.

12 Global ozone change 1980 Now ~ 2100 Observations Models Based on ODS abundances and modeling calculations, estimates of “recovery to pre-1980 value” are now: ~ 2050 at mid-latitudes (better estimates of the “banks” of ODSs) ~ 2065 for the Antarctic ozone hole (age of air) ~ 2050 for the Arctic springtime ozone depletions Volcanoes can influence ozone levels, but only for a few years This is a complex issue with non-linear dependencies… Is this treated adequately? Appropriately? People care about these dates! (& they are often misunderstood!) Explaining the Past and Predicting the Future

13 Return of the ozone layer to pre-1980 values (when it was not significantly influenced by ODS) is considered “recovery”. Multiple factors contribute to the return of ozone to pre-1980 values. Climate change and ODS will affect the future of ozone layer. “Recovery”: What is it? Concept Model Reality?

14 Return of the ozone layer to pre-1980 values (when it was not significantly influenced by ODS) is considered “recovery”. An operational definition? A better definition? Do we need a definition? Is it a good concept? “Beyond” natural variability? Would the variability get larger? Smaller? Is 1980 a good “baseline?” - chemically, dynamically? Other factors (e.g., solar cycle)? Do we talk about “super or sub recovery?” Is it essential that all models agree? Is explaining the past essential for predicting the future? “Recovery”: A big issue

15 Multiple factors contribute to the return of ozone to pre-1980 values. Climate change and ODS will affect the future of ozone layer. Other factors? The contributions of “polar ozone depletions” on mid-latitude ozone. What are the vertical distributions of the ozone layer changes? Is the Upper Strat the best place to look for effect of ODSs? Decreases in ODS emissions already achieved by MP is the dominant factor in ozone returning towards its pre-1980 values- At least in the next couple of decades.. Later in the century? Difficulties in attribution when changes are smaller… “Recovery”: A big issue, contd.

16 Explaining the Past and Predicting the Future: UV Basic understanding of variation in UV with ozone remains unchanged. Large global ozone depletions in a world without MP would have led to very large UV increases Now ~ 2100 Ultraviolet radiation change UV changes will not be a major driver Impacts of stratospheric ozone changes on climate and the troposphere (weather, predictability, etc.) are the emerging issues

17 Thank you for your attention