The Polar Amplification of Global Warming in the Absence of the Ice Albedo Feedback

1
The Polar Amplification of Global Warming in the
Absence of the Ice Albedo Feedback
Aaron Donohoe and David Battisti University
of Washington
2
Annual Mean Temperature change in AGCM
(CAM4)simulation of Last Glacial Maximum (LGM)
and four times CO2 (Quad) as compared to
pre-industrial (PI)
Delta Temperature (K)
Latitude
Delta Temperature (K)
(Data Camille Li)
3
Meridional anomaly of annual mean temperature
change
5
0 K
-5
Latitude
4
2
K
0
-2
-4

• Surface Polar Amplification
• Indication of the Opposite Aloft

4
Seasonal Cycle of Temperature
Change in Seasonal Amplitude of Temp.
Seasonal Amplitude of Temperature PI run
5 0 -5
K
K
2
K
0
Latitude
-2

• Smaller amplitude surface seasonal cycle in
  warmer climate
• Opposite true aloft

5
How does the system respond to CO2 only?

• GFDL 2.1 AGCM coupled to a 50 meter slab ocean
• NO LAND - aquaplanet
• NO ICE
• Ensemble of runs with 180 ppm (LGM),
• 350 ppm (P ), and 1300 ppm (QUAD) CO2

(Thanks to Dargan Frierson)
6
Aquaplanet Temperature Changes
Annual Mean, Meridional Anomaly
QUAD - LGM
Annual Mean
K
K
Seasonal Amplitude
QUAD - LGM
K
K
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QUAD LGM Change in global annual mean energy
budget
SWABS
LWA?
8.2
-0.2
ATMOSPHERE
34.9
-48.5
9.5
-3.9
LH
SENS
SWTRANS
LWA?
LWS?
SWREF
48.5
-9.5
-34.9
-8.2
0.2
3.9
SURFACE
ALL TERMS ARE IN W/m2
8
Water Vapor as a SW Absorber
SW Heating by Water Vapor
0 50 100 150 200 250
QUAD LGM SW heating
(Figure Robert Rhode Global Warming Art Project)
(Chou and Lee 1996)
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SW absorption and the equator to pole gradient
Meridional Anomaly of Annual Mean
Global Annual Mean
?S Meridional Anomaly of Solar Insolation
S(1-a)
-?S(1-a)
?S(1-a)
ß 3.5 Absorption
70 W/m2
-70 W/m2
ßS(1-a)
-ß?S(1-a)
ß?S(1-a)
8 W/m2
2.5 W/m2
-2.5 W/m2
-ßS(1-a)
-ß?S(1-a)
ß?S(1-a)
-8 W/m2
-2.5 W/m2
2.5 W/m2
Tropics
Extratropics
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SW Absorption and the Seasonal Cycle
SUMMER SE Seasonal Extratropical
Insolation Anomaly
WINTER
SE(1-a)
- SE(1-a)
140 W/m2
-140 W/m2
- ßSE(1-a)
Enhanced Seasonal Cycle
5.5 W/m2
-5.5W/m2
Reduced Seasonal Cycle
ßSE(1-a)
-5.5 W/m2
5.5 W/m2
Extratropics
Extratropics
11
QUAD LGM change in meridional anomaly of SW
clearsky heating
12
(Quad LGM) Change in seasonal amplitude of
clearsky SW heating
13
Conclusions

• Warmer planets exhibit SURFACE polar
  amplification of temperature change and a
  reduction of the seasonal cycle independent of an
  ice albdeo feedback
• Enhanced SW absorption by water vapor in a warmer
  world explains both the polar amplification and
  the reduction of the seasonal cycle of
  temperature
• How much might this mechanism contribute to the
  real world?

Percent Change in Seasonal Cycle Aquaplanet
Simulations

14
Clearsky SW Heating in Aquaplanet runs
Annual Mean, Meridional Anomaly
Annual Mean
k/day
k/day
k/day
15
Water Vapor as a SW Absorber
SW Heating by Water Vapor
0 0.5 1.0 1.5 2.0 2.5
QUAD LGM SW heating
(Figure Robert Rhode Global Warming Art Project)
(Chou and Lee 1996)
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Annual Mean Heat Transport in Aquaplanet
Simulations