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 0 K 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

7. QUAD – LGM Change in global annual mean energy budget SWABS LWA↑ +8.2 -0.2 ATMOSPHERE +34.9 -48.5 +9.5 -3.9 SWTRANS LH SENS 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)

9. Meridional Anomaly of Annual Mean Global Annual Mean SW absorption and the equator to pole gradient ΔS = Meridional Anomaly of Solar Insolation [S](1-α) -ΔS(1-α) +ΔS(1-α) β = +3.5% Absorption +70 W/m2 -70 W/m2 +β[S](1-α) +βΔS(1-α) -βΔS(1-α) +8 W/m2 +2.5 W/m2 -2.5 W/m2 -β[S](1-α) -βΔS(1-α) +βΔS(1-α) -8 W/m2 -2.5 W/m2 +2.5 W/m2 Tropics Extratropics

10. + βSE’(1-α) - βSE’(1-α) SW Absorption and the Seasonal Cycle SUMMER SE’ = Seasonal Extratropical Insolation Anomaly WINTER + SE’(1-α) - SE’(1-α) +140 W/m2 -140 W/m2 - βSE’(1-α) Enhanced Seasonal Cycle +5.5 W/m2 -5.5W/m2 Reduced Seasonal Cycle + βSE’(1-α) -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)

16. Annual Mean Heat Transport in Aquaplanet Simulations