1. Attribution of Stratospheric Temperature Trends to Forcings A coupled chemistry-climate model (CCM) study Richard S. Stolarski NASA GSFC In collaboration with Steven Pawson, Anne Douglass, Paul Newman, Mark Schoeberl and Eric Nielsen SPARC Temperature Trends Meeting, Washington DC, April 12-13, 2007

2. Difference in Temperature between Past and Future Simulations Past simulation used observed SSTs (1950- 2005). Future simulation used model-generated SSTs (1996-2100). Overlap period was used to adjust future temperatures to make a consistent time series. Contours indicate the latitude and altitude dependence of the adjustments. All temperatures used in this analysis are annual means.

3. Model Simulated Temperature Change 1979-1998 (K/decade) Upper Stratospheric Cooling by Radiation to Space Ozone Hole Cooling Dynamic Response to Ozone Hole Tropospheric Warming Can we quantitatively separate the contributions of ozone change and greenhouse gases in our simulations?

4. Fitting Model Temperature Time Series to EESC, CO 2, and CH 4 Terms: Midlatitude Upper Stratosphere We will fit this function with 4 terms: Mean + a 1 EESC + a 2 CO 2 + a 3 CH 4

5. Thin line: model output Thick line: Fit with All Terms CO 2 Term (+mean) EESC Term (+mean) CH 4 Term (+mean) Fitting Model Temperature Time Series to EESC, CO 2, and CH 4 Terms: Midlatitude Upper Stratosphere Fit uses entire 140-year simulation time series

6. Fitting Model Temperature Time Series to EESC, CO 2, and CH 4 Terms: Midlatitude Upper Stratosphere Thin line: model output Thick line: Fit with All Terms CO 2 Term (+mean) EESC Term (+mean) CH 4 Term (+mean) Change from 1979-1998 -1.9K EESC -0.7K CO2 -0.4K CH4 -3.0K Total

7. Thin line: model output Thick line: Fit with All Terms CO 2 Term (+mean) EESC Term (+mean) CH 4 Term (+mean) Change from 1979-1998 -1.9K EESC -0.7K CO2 -0.4K CH4 -3.0K Total Change from 2006-2025 +0.7K EESC -1.3K CO2 -0.6K CH4 -1.2K Total Fitting Model Temperature Time Series to EESC, CO 2, and CH 4 Terms: Midlatitude Upper Stratosphere

8. Relative Contribution of EESC, CO 2, and CH 4 to Temperature Change at 1 hPa 40 o N

9. How long must the record be to separate effects by time-series analysis?

10. Effect of Length of Record on Fitting: Graphical Illustration: 40 o N, 1hPa

11. Effect of Length of Record on Fitting: Graphical Illustration: 40 o N, 1hPa Continued

12. Sensitivity to EESC and CO 2 as a Function of Endpoint of Output 40 o N 1hPa These are trends from 1979 through 1998 calculated from output from 1979 through various end years. Thin lines in left panels are .

13. Some Other Locations in the Stratosphere

14. Northern Mid Latitude Lower Stratosphere Methane term includes effects of increased HO x 60% EESC

15. Sensitivity to EESC and CO 2 as a Function of Endpoint of Output 40 o N 50hPa Statistically significant after 2020, but uncertainty never gets less than 50%

16. Fitting Model Temperature Time Series to EESC, CO 2, and CH 4 Terms: Antarctic Lower Stratosphere Thin line: model output Thick line: Fit with All Terms CO 2 Term (+mean) EESC Term (+mean) CH 4 Term (+mean) Antarctic lower stratospheric temperature is dominated by ozone hole from ~1960 through 2100. Greenhouse gas terms are minor.

17. Fitting Model Temperature Time Series to EESC, CO 2, and CH 4 Terms: Antarctic Upper Stratosphere Antarctic upper stratospheric temperature increases due to dynamic response to ozone hole through 2000. Thereafter, temperature decreases as ozone hole recovers and GHGs continue to cause decrease.

18. Map of EESC Term Using Output from 1979 to: 2010 20252040 20152020 2060 Color Regions are Statistically Significant

19. Greenhouse Gas (CO 2 ) Term Using Output from 1979 to: 2010 2025 2040 20152020 2060

20. Some Tentative Conclusions Simulations indicate about 2/3 of annual temperature trend of upper stratosphere due to ozone decrease Simulations indicate about 60% of annual temperature trend of lower mid latitude stratosphere due to ozone decrease Upper stratospheric ozone effect should be able to be separated from greenhouse gas effect with present data: a few more years are needed to reduce uncertainties (of course this assumes a lot about the simulation’s representation of variability and its lack of QBO and solar cycle).