1. Can Geoengineering save the Greenland ice sheet?
Dan Lunt Andy Ridgwell, Paul Valdes
Dan Lunt, Copenhagen, 2009

2. Eventual near-total melting at CO2 >= 550ppmv
[Alley et al, Science, 2005]
Eventual near-total melting at CO2 >= 550ppmv
Dan Lunt, Copenhagen, 2009

3. [Keith, Nature, 2001]
Dan Lunt, Copenhagen, 2009

4. What did we do….? The General Circulation Model (GCM)
HadCM3(L) - “State of the art” (for > ~100 year simulations)
Dan Lunt, Copenhagen, 2009

5. (1) Pre-industrial (PI) (2) High CO2 (4* PI),
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
Dan Lunt, Copenhagen, 2009

6. Annual mean surface temperature change Geoengineered - pre-industrial
Lunt et al, GRL, 2008
Annual mean surface temperature change Geoengineered - pre-industrial
Dan Lunt, Copenhagen, 2009

7. Precipitation:
ENSO: THC:
Dan Lunt, Copenhagen, 2009

8. “Sunshade World” Precip “CO2 World” Precip
“Sunshade World” Temp
“CO2 World” Temp
“Sunshade World” Precip
“CO2 World” Precip
Dan Lunt, Copenhagen, 2009

9. What about Greenland?? “Sunshade World” Temp “CO2 World” Temp
“Sunshade World” Precip
“CO2 World” Precip
What about Greenland??
Dan Lunt, Copenhagen, 2009

10. The ice-sheet model GLIMMER
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]
Dan Lunt, Copenhagen, 2009

11. 4*CO2, Lunt et al, Phil, Trans. Roy. Soc. A, 2009
control
4*CO2, Lunt et al, Phil, Trans. Roy. Soc. A, 2009
4*CO2, Ridley et al, Journal of Climate, 2005
Dan Lunt, Copenhagen, 2009

12. 4*CO2, Lunt et al, Phil, Trans. Roy. Soc. A, 2009 4*CO2, geoengineered
control
4*CO2, Lunt et al, Phil, Trans. Roy. Soc. A, 2009
4*CO2, geoengineered
Dan Lunt, Copenhagen, 2009

13. Conclusions and Questions
‘Sunshade’ geoengineering will lead to warmer poles, cooler tropics. Effects amplified by snow and seaice albedo feedbacks.
Decreased intensity of the hydrological cycle.
Reduced ENSO variability, increased Atlantic MOC.
BUT….changes are small relative to the unmitigated case…..
and it could stop ‘dangerous’ sea level rise……
HOWEVER…….
Dan Lunt, Copenhagen, 2009

14. Risks of catastrophic failure?
Ocean acidification?
Risks of catastrophic failure?
Ice sheet model......?
Lack of albedo feedbacks
Lack of ‘fast’ processes
Lack of ‘second order’ physics
What about Antarctica?
Dan Lunt, Copenhagen, 2009