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Effects of GeoEngineering on the Southern Ocean. Judy Twedt ~ Kelly McCusker ~ Cecilia Bitz June 5, 2012. Reuters. A Tale of Two Geoengineering Strategies. increase the earth’s reflectance with stratospheric sulfate aerosols. remove greenhouse gasses. i ncreased winds; - PowerPoint PPT Presentation
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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