1. Global-mean energy balance

2. Spatial Radiation Imbalance Distribution of solar forcing as function of latitude

3. 100 W/m 2 300 W/m 2 E IN (SW) E OUT (LW) Top-of-atmosphere radiation imbalance

4. Cause of the seasons

5. Cause of the seasons (better)

6. Seasonal cycle in net solar radiation

7. Seasonal cycle in terrestrial radiation (outgoing infrared)

8. Seasonal cycle in net radiation (solar minus terrestrial)

9. Seasonal cycle in temperature

10. Seasonal cycle in temperature – land responds quickly

11. Seasonal cycle in temperature – ocean responds slowly

12. Amplitude in seasonal cycle. (at least) three things going on here…

13. In detail: insolation as a function of latitude Hartmann, 1994 Why are December and June not symmetric?

14. In detail: what does Earth do with this insolation? albedo as a function of latitude Wells, 1997 what causes this pattern?

15. Albedo Absorbed insolation (1-  ) x incident insolation Emitted terrestrial radiation Net radiation balance (= absorbed rad n - emitted rad n ) In detail: energy balance as a function of latitude Peixoto and Oort, 1992

16. In detail: net radiation balance at top of atmosphere Poleward Heat flux More radiation is absorbed than emitted in the tropics more radiation is emitted than absorbed at high latitudes Implies an energy flux from the equator to the high latitudes

17. In detail: net heat flux from tropics: Average radiation imbalance ~ 50 Wm -2 Surface Area of tropics = 2  R e 2 sin (30 o ) Total heat flux from tropics = surface area x imbalance = 6.4 x 10 15 W = 10,000 times global energy production. = 1 Baringer size impact craters every 11 mins!! 1 Baringer = 10 9 tonnes of TNT (1 tonne TNT = 4.2 x 10 9 J)

18. In detail: poleward heat transport Total OceanAtmosphere Trenberth and Caron, 2001 1 Petawatt = 10 15 W Ocean transports more heat in low latitudes (& net transport of heat across the equator) Atmosphere transports more in middle and high latitudes

20. Aside: longwave (infrared) emissions to space as a function of surface temperature n.b. why not use  T 4 ? We’ve used Stefan Boltman law: longwave radiation =  T 4 Make our lives easier: longwave radiation = A + BT From data: