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

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] use less energy emit less CO 2 change climate adapt

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

(1) Stratospheric sulphate aerosols Pinatubo eruption, 1991

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

(3) Cloud seeding

(4) Crop albedo geoengineering Ridgwell et al. 2009

(5) Iron fertilisation  SOIREE iron fertilisation experiment.

(6) Biochar

Royal Society Report on Geoengineering

 Fully dynamic atmosphere, slab ocean: CCM3  3 experiments: pre-industrial, 2*CO2, geoengineered CO 2 radiation pertubationSolar radiation pertubation

ΔT due to CO 2 doubling alone ΔT due to CO 2 doubling and reduction in solar constant – ‘geoengineered’

ΔT due to 4*CO 2 alone ΔT due to 4*CO 2 and reduction in solar constant – ‘geoengineered’ Seaice, control Seaice, geoengineered Seaice, 4*CO 2

 GCM ocean, Energy balance atmosphere: UVic  2 experiments: A2 scenario, geoengineered Plants use water more efficiently at high CO 2 – less evapotranspiration

Failure of geoengineering A2 geoengineered

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

Temperature anomaly, Geo - PreInd Solar forcing, TOA Solar forcing has strong meridional gradient. CO 2 forcing balances in global mean but is more meridionally homogeneous

Annual mean surface temperature change Geoengineered - pre-industrial

Annual mean sea ice change Geoengineered - pre-industrial

Precipitation Soil moisture Storm tracks (500mbar EKE)

ENSO Control: σ=0.46 Geoengineered: σ=0.35

“Sunshade World” Temp “CO 2 World” Precip“Sunshade World” Precip “CO 2 World” Temp Lunt et al, 2008

“Sunshade World” Temp “CO 2 World” Precip“Sunshade World” Precip “CO 2 World” Temp What about Greenland??

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]

control4*CO2, Ridley et al, Journal of Climate, *CO 2

control4*CO 2 4*CO 2, geoengineered Irvine et al, 2009

4*CO 2 4*CO 2 with sunshade SAT Precip Lunt et al *CO 2 with sunshade Anomaly compared to pre-industrial climate Sunshade Geoengineering

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

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