1. Judy Twedt ~ Kelly McCusker ~ Cecilia Bitz June 5, 2012 Judy Twedt ~ Kelly McCusker ~ Cecilia Bitz June 5, 2012 Effects of GeoEngineering on the Southern Ocean Reuters

2. A Tale of Two Geoengineering Strategies increase the earth’s reflectance with stratospheric sulfate aerosols remove greenhouse gasses decrease global mean surface temperature increased winds; more upwelling Southern Ocean barely cools decreased winds; less upwelling Southern Ocean Cools feasible now hypothetically feasible

3. Increasing Albedo with Sulfate Aerosols (Kelly’s work) Run RCP 8.5 emissions scenarios on CCSM4, with *full ocean dynamics* In 2035, increase Earth’s albedo by prescribing stratospheric concentrations of sulfate aerosols on top of RCP 8.5 greenhouse gasses Compare with 20 th Century Climatology (1970-1999) http://www.noaa.gov/features/protecting_0808/images/volcanoashcloud.jpg

4. RCP 8.5 McCusker, 2012 Annual Mean Global Temperature 288 K 19602060

5. RCP 8.5 McCusker, 2012 Sulfate Engineering Annual Mean Global Temperature 288 K 19602060

6. RCP 8.5 McCusker, 2012 Annual Mean Global Temp (k) Sulfate Engineering Shut-Off 288 K 19602060

7. RCP 8.5 McCusker, 2012 Annual Mean Global Temperature Sulfate Engineering Shut-Off 1850 Reference 288 K 19602060

8. return to 1988 GHG concentrations Annual Mean Global Temperature 288 K 1960 2060

9. return to 1988 GHG concentrations Annual Mean Global Temperature 288 K 1960 2060

10. Surface Temperature Differences (k) Annual Avg of Sulfate Engineering (2045-2054) – 20 th C (1970-1999) Sulfates Cool the Arctic more than the Antarctic

11. Vertical Temperature Profile Annual Avg of Sulfate Engineering (2045-2054) – 20 th C (1970-1999) pause Temperature Difference Sulfates absorb sw radiation in the stratosphere and are confounded with greenhouse gases. Result: a poleward shift in surface westerlies

12. Near Surface Winds Sulfate Engineering (2045-2054) – 20 th C (1970-1999) The change in the sulfate run is a strengthening of existing Antarctic winds increased westerlies 1970-1999 control

13. Motivating Questions Why didn’t the Southern Ocean cool? Are winds the culprit? Does the combination of greenhouse gasses & sulfates increase the winds and induce warm water upwelling in the Southern Ocean?

14. Modeling Wish Fulfillment (Greenhouse Gas Removal) I ran a branch from the RCP 8.5 scenario In 2035, dropped the GHG emissions to 1988 concentrations; ran 50 years Prescribed Greenhouse Gas Concentrations CO2 concentrations of 350 ppm have been proposed as target concentration by Hansen et. al., 2008 CO 2 CH 4 N 2 O CFC-11 CFC-12 350 ppm

15. Return to 1988 concentrations (just a reminder) sulfate geoengineering 2045 – 2054 climatology

16. Surface Temperature Difference Annual Avg (2045 – 2054) of GHG Removal – Sulfate Engineering Although the global mean surface temp is warmer, the Southern Ocean surface is already cooler!

17. Wind Stress Difference Annual Avg (2045 – 2054) of GHG Removal – Sulfate Engineering surface westerlies over Antarctica are weaker with greenhouse gas removal

18. Zonal Avg Ekman Pumping Upwelling *negative* Antarctica Downwelling *positive* ‘zero-line’ of the greenhouse gas removal run is NORTH of the sulfate run 90 S44 S

19. Comparison of CCSM4 Cooling Scenarios Stratospheric Sulfates Rapid reduction in global mean surface temp Increased westerlies over the Southern Ocean – more upwelling, more heating from below Not a viable means of protecting the Antarctic ice sheet Greenhouse Gas Removal Reduction in global mean surface temp Decreased Ekman pumping Ekman transport shifts northward Cooling over the Southern Ocean

20. Next Steps Dig deeper into the ocean data and look at the subsurface ocean response Probe the response rate: how does the Southern Ocean respond so quickly? Remove MORE greenhouse gasses: simulate a return to pre-industrial forcing ? ? ? ?

21. I’d like to thank Kelly McCusker and Cecilia Bitz for their help and terrific feedback. That said, any errors are my own.

22. xkcd.com/154