Past and Future Climate Past and Future Climate SimulationSimulation

Lecture 5Lecture 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]

[Keith, Annu. Rev. Energy Environ., 2000]

use less energy emit less CO2 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

CO2 radiation pertubation Solar radiation pertubation

ΔT due to CO2 doubling alone

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

ΔT due to 4*CO2 alone

ΔT due to 4*CO2 and reduction in solar constant – ‘geoengineered’

Seaice, control

Seaice, geoengineered

Seaice, 4*CO2

GCM ocean, Energy balance atmosphere: UVic

2 experiments: A2 scenario, geoengineered

Plants use water more efficiently at high CO2 – less evapotranspiration

Failure of geoengineering

A2 geoengineered

3 simulations:

(1) Pre-industrial (PI)

(2) High CO2 (4* PI),

(3) High CO2 (4* PI), reduced solar constant

4*CO2

Pre-industrial

Geoengineered4.2% reduction in solar constant = 57 W/m2

Temperature anomaly, Geo - PreInd

Solar forcing, TOA

Solar forcing has strong meridional gradient. CO2 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

“CO2 World” Precip“Sunshade World” Precip

“CO2 World” Temp

Lunt et al, 2008

“Sunshade World” Temp

“CO2 World” Precip“Sunshade World” Precip

“CO2 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]

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

4*CO2

control 4*CO2 4*CO2, geoengineered

Irvine et al, 2009

4*CO2

4*CO2

4*CO2 with sunshade

SAT

Precip

Lunt et al. 2008

4*CO2 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 Should we Geoengineer the climate?climate?

What are the climate changes? Can we What are the climate changes? Can we know them well enough?know them well enough?

Which scheme (or combination of schemes) Which scheme (or combination of schemes) minimizes minimizes damagedamage??

Who decides what Who decides what damagesdamages matter most? matter most? How to deal with the “winners” and How to deal with the “winners” and

“losers”?“losers”? ““Moral Hazard”Moral Hazard” Is it an ethical response to global warming?Is it an ethical response to global warming?