Past and Future Climate Simulation Lecture 5

1. Past and Future Climate Simulation Lecture 5 Geoengineering our Climate • What is geoengineering? • Focus on sunshade geoengineering • Should we geoengineer our climate?

2. use less energy emit less CO2 change climate adapt [Keith, Annu. Rev. Energy Environ., 2000] So, what is geoengineering…..? “The intentional large-scale manipulation of the environment, particularly manipulation that is intended to reduce undesired anthropogenic climate change’’ [Keith, Annu. Rev. Energy Environ., 2000]

3. [based on Keith, Nature, 2001] ~100 papers to date….mostly ‘opinion’ pieces (cf. at least 50,000 on climate change!).

4. (1) Stratospheric sulphate aerosols Pinatubo eruption, 1991

5. 15 m (2) Solar “sunshade” 5 m 60 cm [Angel, PNAS, 2006] They would weigh a gram each. ~15 trillion within a 100,000- km-long cloud. “It seems feasible that it could be developed and deployed in 25 years at a cost of a few trillion dollars” [Angel, PNAS, 2006]

6. (3) Cloud seeding

7. (4) Crop albedo geoengineering Ridgwell et al. 2009

8. (5) Iron fertilisation • SOIREE iron fertilisation experiment.

9. (6) Biochar

10. Royal Society Report on Geoengineering

11. Fully dynamic atmosphere, slab ocean: CCM3 • 3 experiments: pre-industrial, 2*CO2, geoengineered CO2 radiation pertubation Solar radiation pertubation

12. ΔT due to CO2 doubling alone ΔT due to CO2 doubling and reduction in solar constant – ‘geoengineered’

13. Seaice, control Seaice, 4*CO2 ΔT due to 4*CO2 alone Seaice, geoengineered ΔT due to 4*CO2 and reduction in solar constant – ‘geoengineered’

14. GCM ocean, Energy balance atmosphere: UVic • 2 experiments: A2 scenario, geoengineered Plants use water more efficiently at high CO2 – less evapotranspiration

15. Failure of geoengineering geoengineered A2

16. 3 simulations: (1) Pre-industrial (PI) (2) High CO2 (4* PI), (3) High CO2 (4* PI), reduced solar constant 4*CO2 4.2% reduction in solar constant = 57 W/m2 Geoengineered Pre-industrial

17. Solar forcing has strong meridional gradient. CO2 forcing balances in global mean but is more meridionally homogeneous Solar forcing, TOA Temperature anomaly, Geo - PreInd

18. Annual mean surface temperature change Geoengineered - pre-industrial

19. Annual mean sea ice change Geoengineered - pre-industrial

20. Precipitation Soil moisture Storm tracks (500mbar EKE)

21. ENSO Control: σ=0.46 Geoengineered: σ=0.35

22. “Sunshade World” Temp “CO2 World” Temp “Sunshade World” Precip “CO2 World” Precip Lunt et al, 2008

23. “Sunshade World” Temp “CO2 World” Temp “Sunshade World” Precip “CO2 World” Precip What about Greenland??

24. The ice-sheet model • Ice-sheet model – GLIMMER. Based on Payne (1999). • Predicts evolution of ice-sheet geometry (extent, elevation). • Mass balance scheme (surface of ice-sheet) • Ice-sheet dynamics • Driven offline by temperature and precipitation from the GCM. Temperature downscaled using high-resolution orography and a constant lapse rate. [Letreguilly et al, 1991] GLIMMER [Stone et al, in prep]

25. control 4*CO2 4*CO2, Ridley et al, Journal of Climate, 2005

26. control 4*CO2 4*CO2, geoengineered Irvine et al, 2009

27. Sunshade Geoengineering Anomaly compared to pre-industrial climate 4*CO2 4*CO2 with sunshade SAT 4*CO2 4*CO2 with sunshade Precip Lunt et al. 2008

28. Fractional Sunshade Geoengineering – regional issues Irvine et al, submitted to GRL. Irvine et al, 2010

29. Should we Geoengineer the climate? • What are the climate changes? Can we know them well enough? • Which scheme (or combination of schemes) minimizes damage? • Who decides what damages matter most? • How to deal with the “winners” and “losers”? • “Moral Hazard” • Is it an ethical response to global warming?