Judy Twedt ~ Kelly McCusker ~ Cecilia BitzJune 5, 2012

Effects of GeoEngineering on the

Southern Ocean

Reuters

A Tale of Two Geoengineering Strategies

increase the earth’s reflectance with stratospheric sulfate aerosols

remove greenhousegasses

decrease global mean surfacetemperature

increased winds;more upwelling

Southern Oceanbarely cools

decreased winds; less upwelling

Southern Ocean Coolsfeasible now

hypothetically feasible

Increasing Albedo with

Sulfate Aerosols(Kelly’s work)

• Run RCP 8.5 emissions scenarios on CCSM4, with *full ocean dynamics*

•In 2035, increase Earth’s albedo by prescribing stratospheric concentrations of sulfate aerosols on top of RCP 8.5 greenhouse gasses

•Compare with 20th Century Climatology (1970-1999)

http://www.noaa.gov/features/protecting_0808/images/volcanoashcloud.jpg

RCP 8.5

McCusker, 2012

Annual Mean Global Temperature

288 K

1960 2060

RCP 8.5

McCusker, 2012

Sulfate Engineering

Annual Mean Global Temperature

288 K

1960 2060

RCP 8.5

McCusker, 2012

Annual MeanGlobal Temp (k)

Sulfate EngineeringShut-Off

288 K

1960 2060

RCP 8.5

McCusker, 2012

Annual Mean Global Temperature

Sulfate Engineering

Shut-Off

1850 Reference

288 K

1960 2060

return to 1988 GHG concentrations

Annual Mean Global Temperature

288 K

1960 2060

return to 1988 GHG concentrations

Annual Mean Global Temperature

288 K

1960 2060

Surface Temperature Differences (k)

Annual Avg of Sulfate Engineering (2045-2054) – 20th C (1970-1999)

Sulfates Cool the Arctic more than the Antarctic

Vertical Temperature Profile Annual Avg of

Sulfate Engineering (2045-2054) – 20th C (1970-1999)

pause Temperature Difference

• Sulfates absorb sw radiation in the stratosphere and are confounded with greenhouse gases.

• Result: a poleward shift in surface westerlies

Near Surface Winds Sulfate Engineering (2045-2054) – 20th C (1970-1999)

The change in the sulfate run is a strengthening of existing Antarctic winds

increased westerlies1970-1999 control

Motivating Questions

• Why didn’t the Southern Ocean cool?• Are winds the culprit? Does the combination of greenhouse gasses & sulfates increase the winds and induce warm water upwelling in the Southern Ocean?

Modeling Wish Fulfillment (Greenhouse Gas Removal)• I ran a branch from the RCP 8.5 scenario

• In 2035, dropped the GHG emissions to 1988 concentrations; ran 50 yearsPrescribed Greenhouse Gas Concentrations

CO2 concentrations of 350 ppm have been proposed as target concentration by Hansen et. al., 2008

CO2 CH4N2O

CFC-11CFC-12

350ppm

Return to 1988 concentrations

(just a reminder)

sulfate geoengineering

2045 – 2054climatology

Surface Temperature DifferenceAnnual Avg (2045 – 2054) of

GHG Removal – Sulfate Engineering

Although the global mean surface temp is warmer, the Southern Ocean surface is already cooler!

Wind Stress DifferenceAnnual Avg (2045 – 2054) of

GHG Removal – Sulfate Engineering

surface westerlies over Antarctica are weaker with greenhouse gas removal

Zonal Avg Ekman Pumping

Upwelling *negative*

Anta

rcti

ca

Downwelling *positive*

‘zero-line’ of the greenhouse gas removal run is NORTH of the sulfate run

90 S 44 S

Comparison of CCSM4 Cooling Scenarios

Stratospheric Sulfates• Rapid reduction in

global mean surface temp

• Increased westerlies over the Southern Ocean – more upwelling, more heating from below

• Not a viable means of protecting the Antarctic ice sheet

Greenhouse Gas Removal• Reduction in global

mean surface temp• Decreased Ekman

pumping• Ekman transport shifts

northward• Cooling over the

Southern Ocean

Next Steps• Dig deeper into the ocean data and

look at the subsurface ocean response

• Probe the response rate: how does the Southern Ocean respond so quickly?

• Remove MORE greenhouse gasses: simulate a return to pre-industrial forcing

• ? ? ? ?

I’d like to thankKelly McCusker and Cecilia Bitz

for their help and terrific feedback.That said, any errors are my own.

xkcd.com/154