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Past and Future Climate
Simulation
Lecture 5
Geoengineering our Climate
 What is geoengineering?
 Focus on sunshade geoengineering
 Should we geoengineer our climate?
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]
[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
15 m
(2) Solar “sunshade”
5m
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]
(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’
Seaice, control
Seaice, 4*CO2
ΔT due to 4*CO2
alone
Seaice, geoengineered
ΔT due to 4*CO2
and reduction in
solar constant –
‘geoengineered’
 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
4.2% reduction in
solar constant = 57
W/m2
Geoengineered
Pre-industrial
Solar forcing has strong meridional
gradient. CO2 forcing balances in
global mean but is more meridionally
homogeneous
Solar forcing, TOA
Temperature anomaly, Geo - PreInd
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
“Sunshade World” Precip
Lunt et al, 2008
“CO2 World” Temp
“CO2 World” Precip
“Sunshade World” Temp
“Sunshade World” Precip
“CO2 World” Temp
“CO2 World” Precip
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 highresolution orography and a constant
lapse rate.
[Letreguilly et al, 1991]
GLIMMER
[Stone et al, in prep]
control
4*CO2
4*CO2, Ridley et al,
Journal of Climate, 2005
control
Irvine et al, 2009
4*CO2
4*CO2, geoengineered
Sunshade Geoengineering
Anomaly compared to pre-industrial climate
4*CO2
4*CO2 with sunshade
4*CO2
4*CO2 with sunshade
SAT
Precip
Lunt et al. 2008
Fractional Sunshade Geoengineering – regional issues
Irvine et al, submitted to GRL.
Irvine et al, 2010
Should we Geoengineer the climate?
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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?