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

Albedo Feedback

Aaron Donohoe and David Battisti University of Washington

Annual Mean Temperature change in AGCM (CAM4)simulation of Last Glacial Maximum (LGM) and four

times CO2 (Quad) as compared to pre-industrial (PI)

Latitude

Delta Temperature (K)

Delta Temperature (K)

(Data : Camille Li)

Meridional anomaly of annual mean temperature change

Latitude

•Surface Polar Amplification

•Indication of the Opposite Aloft

-4

0

42

-2K

5

0 K

-5

Seasonal Cycle of Temperature

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

Latitude

K

K

Seasonal Amplitude of Temperature – PI run

Change in Seasonal Amplitude of Temp.

K

5

0

-5

0

2

-2

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)

Aquaplanet Temperature Changes

Annual Mean

Annual Mean, Meridional AnomalyQUAD - LGM

K

K

K

K

QUAD - LGMSeasonal Amplitude

QUAD – LGM Change in global annual mean energy budget

SURFACE

ATMOSPHERE

LWA↓

-48.5

+48.5

LWS↑

+34.9

-34.9

LWA↑

-0.2

SWABS

+8.2

-8.2

LH

-9.5

+9.5

SENS

+3.9

-3.9

ALL TERMS ARE IN W/m2

SWREF

+0.2

SWTRANS

Water Vapor as a SW Absorber

SW Heating by Water Vapor

(Chou and Lee 1996)(Figure: Robert RhodeGlobal Warming Art Project)

QUAD – LGMSW heating

0 50 100 150 200 250

SW absorption and the equator to pole gradient

[S](1-α)

β = +3.5%Absorption

+β[S](1-α)

-β[S](1-α)

+8 W/m2

-8 W/m2

Global Annual Mean Meridional Anomaly of Annual Mean

Tropics Extratropics

-ΔS(1-α)

+βΔS(1-α)

-βΔS(1-α)

+ΔS(1-α)

+βΔS(1-α)

-βΔS(1-α)

+2.5 W/m2

-2.5 W/m2

-2.5 W/m2

+2.5 W/m2

ΔS = Meridional Anomaly of Solar Insolation

+70 W/m2 -70 W/m2

SW Absorption and the Seasonal Cycle SUMMER SE’ = Seasonal Extratropical Insolation Anomaly

Extratropics Extratropics

+ SE’(1-α) - SE’(1-α)

+ βSE’(1-α)

- βSE’(1-α)+ βSE’(1-α)

- βSE’(1-α)

+140 W/m2

+5.5 W/m2

-5.5 W/m2

-140 W/m2

-5.5W/m2

+5.5 W/m2

Enhanced Seasonal Cycle

Reduced Seasonal Cycle

WINTER

QUAD – LGM change in meridional anomaly of SW clearsky heating

(Quad – LGM) Change in seasonal amplitude of clearsky SW heating

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

%

Clearsky SW Heating in Aquaplanet runs

Annual MeanAnnual Mean, Meridional Anomaly

k/day

k/day

k/day

Water Vapor as a SW Absorber

SW Heating by Water Vapor

(Chou and Lee 1996)(Figure: Robert RhodeGlobal Warming Art Project)

QUAD – LGMSW heating

0 0.5 1.0 1.5 2.0 2.5

Annual Mean Heat Transport in Aquaplanet Simulations