centennial-scale climate change from decadally-paced explosive … · 2010. 7. 17. · gray –...
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Centennial-scale Climate Change from Decadally-paced Explosive Volcanism
Yafang Zhong and Gifford MillerINSTAAR, University of Colorado at Boulder, USA
Bette Otto-Bliesner, Caspar Ammann, Marika Holland, David Bailey and David Schneider
NCAR, USA
Aslaug GeirsdottirUniversity of Iceland, Iceland
CCSM Workshop on June. 29, 2010
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NH Temperature
NH climate of the past millennium
Time
Col
der
MWPLIA
800AD1950AD 1300AD
Crowley (2000)
The past millennium is characterized by Medieval Warm Period (MWP), Little Iage Age (LIA), and 20th century warming.
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Time
1950AD
1300AD
Step-like changes at 1250-1300AD,~1450AD
NH Temperature Col
der
MWPLIA
800AD1950AD 1300AD
Step-like ice cap expansion during the cooling into the Little Ice Age
Ice cap expansion on N Baffin Island
Anderson et al. (2008)
Crowley (2000)Time
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Possible causes of the Little Ice Age
Volcanic forcing?Centennial-scale response?
Solar irradiance?
Ice cap expansion on N Baffin Island
Anderson et al. (2008)
Uncertainty in reconstruction.
Time
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Possible causes of the Little Ice Age
Solar irradiance?
Ice cap expansion on N Baffin Island
Question: Could the decadally sequenced volcanic eruptions cause centennial-scale response in NH sea ice?
Volcanic forcing? Centennial-scale response?
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Experiments using the CCSM3
Medieval control run:•950AD orbital forcing•Solar constant is 1365 W/m2•1000AD Greenhouse Gas level
280.6ppm CO2, 684.3ppb CH4, 264.5 ppb N2O
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Experiments using the CCSM3 (Cont)
Volcanism experiments•Volcanic forcing: decadally sequenced tropical eruptions in the second half of the 13th century
No volcanic forcing for the 14th centuryTime
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Volcanism experiments•Four runs, randomly selected initial states.
Control run
Experiments using the CCSM3 (Cont)
(1)
(2)(3)
(4)
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Centennial-scale response in NH sea ice in volcanism experiments
SW radiation
Mar ice volume
Sep ice volume
Mar ice area
Sep ice area Time
Gray – CTRL Red – EXP1 Blue – EXP2
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NH sea ice concentration anomalies
Largest anomalies in September occur in the Atlantic sector, which agrees with paleo reconstructions.
SEP MAR ANN12
90-1
299A
D13
00-
1399
AD
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Mass budget of ANN NH sea ice Mass budget of NH annual sea ice
Basal growth
Basal melt
Solid – Volcanism EXP Dashed – CTRL
Time
Sea ice expansion is driven by decreased ice-ocean heat exchange.
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Ice mass budget for Barents Sea region
Basal growth
Basal melt
Time
Sea ice expansion is driven by decreased ice-ocean heat exchange.
Solid – Volcanism EXP Dashed – CTRL
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Sea ice mass budget for west of Greenland
Basal growth
Basal melt
Time
Sea ice expansion is driven by decreased ice-ocean heat exchange.
Solid – Volcanism EXP Dashed – CTRL
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Surface cooling in the North Atlantic and Arctic oceans
Heat flux anomaly is into the Arctic Ocean, not responsible for the ocean cooling
Zonal mean ocean temperature anomalies. Shading: significant at 95% confidence level
Strong cooling at NH high latitudes
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Strong cooling at NH high latitudes
The Arctic Ocean cooling is not caused by surface heat flux changes, but rather by reduced ocean heat transport poleward.
Zonal mean surface heat flux anomaly
Surface cooling in the NH high-latitude and Arctic oceans
Into-the-ocean anomaly
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Changes in the surface ocean
Cooling!
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Changes in the surface ocean
Sustained for >100 years!
Cooling!
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Changes in the surface ocean
Cooling! Freshening! Lightening!
Increased sea ice export (freshwater flux) to and thus weakened convection in the subpolar N Atlantic!
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Decreased heat/salt advection associated with the slowed-down subpolar gyre circulation
Color: ANN sea ice thickness anomalyContour: Sea surface height anomalyVector: Current anomaly
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SummaryThe sequenced volcanism could produce an expanded NH sea ice that is sustainable for >100 years after the removal of volcanic aerosols from the stratosphere.A coupled sea ice-ocean mechanism: Sea ice expands and thickens in response to volcanic aerosol radiative forcing More ice is exported through Fram Strait and the Canadian Achipelago, and melts in the subpolar North Atlantic Cooling and freshening of the surface water in the subpolar N Atlantic, in aid of weakened convection and decreased heat/salt advection Anomalously cold water is advected into the Arctic Ocean and reduces ice-ocean heat exchangePreserves the expanded sea ice
The coupled sea ice-ocean mechanism may be sensitive to the pre-volcanic mean states, such as mixing layer depth in the subpolar N Atlantic.
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Thank you!
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Summary•Sequenced volcanism produced an expanded NH sea ice that sustained for >100 years after the removal of volcanic aerosols from the stratosphere. The largest concentration anomalies occurred in the Atlantic sector of the Arctic, agreeing with paleo data.
•A coupled sea ice-ocean mechanism: Sea ice expands and thickens in response to volcanic aerosol radiative forcing More ice is exported and melts in the subpolar North Atlantic Cooling and freshening of the surface water in the subpolar N Atlantic, in aid of weakened convection and decreased heat/salt advection
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The volcanism experiments showingno centennial-scale response
Pre-volcanic•Shallow mixing layer depth in the subpolar N Atlantic, already weak convection
Post-volcanic•Convective feedback ineffective in the subpolar N Atlantic.•Rapid sea ice growth, increased brine rejection, positive density flux in marginal seas strengthened Atlantic MOC, increased heat transport into the Arctic Sea ice recedes
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Summary
•Sequenced volcanism produced an expanded NH sea ice that sustained for >100 years after the removal of volcanic aerosols from the stratosphere. The largest concentration anomalies occurred in the Atlantic sector of the Arctic, agreeing with paleo data.
•A coupled sea ice-ocean mechanism
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Increased sea ice export to subpolar N Atlantic
Net freshwater flux Freshening effect on the subpolar North Atlantic!
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Centennial-scale responsein NH air temperatureAN
NJJA
DJF
Time
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Medieval ontrol run
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1301
-135
0AD
1351
-13
99AD
Ocean temperature anomaly
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Atlantic MOC in volcanism exps
LRSP1, 2 SRSP1 SRSP21250-1257AD
1259-1268AD
1269-1278AD
1279-1288AD
1289-1298AD
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Control run Vs. LRSP1
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1150-1600AD realistic volcanic forcing
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Decreased oceanic heat transport into the Arctic
Colder water into the Arctic!
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Weakend Atlantic Meridional Overturning Circulation