Climate & Climatic Variation (Chapter 2)

1. Climate & Climatic Variation (Chapter 2)

2. CLIMATE = 1. Statistics of Weather Daily Precipitation - Iowa/Nebraska

3. CLIMATE = 1. Statistics of Weather The expected weather + departures from expected weather

4. CLIMATE Reflects the geophysical processes active at a location…

5. Northeastern Siberia

6. Namibia

7. Amazon Rainforest

8. CLIMATE = …and how they might change (e.g., seasonally)… Winter Daily Precipitation - Iowa/Nebraska

9. CLIMATE = …and how they might change (e.g., seasonally)… Summer Daily Precipitation - Iowa/Nebraska

10. … and in the future! (and of course the past)

11. CLIMATE • Implies samples over a period of time. How long? How frequent? 2. WMO standard: 30 years • which 30? • paleoclimate? 3. There is no universal standard, but must define the interval for the topic at hand

12. CLIMATE Has regular cycles …

13. Grassland - Net Radiation Cycles FLH FSH Diurnal Dry Lake - Net Radiation FSH FLH

14. Cycles Soil Temperature at depths marked Annual

15. CLIMATE Has regular cycles … … with other types of variability superimposed …

16. Climatic Variation and Change (IPCC TAR, Ch. 2) Note: Trends, Abrupt Change, Stationarity

17. Climatic Variation and Change (IPCC TAR, Ch. 2) Note: Quasi-periodic Increased range of variability

18. Climatic Variation and Change Additional Factors • Abrupt change • external conditions (e.g., solar output) • internal feedbacks • passing a threshold (e.g. ice caps melting) 2. Multiple climate states from the same external conditions

19. The Climate System (IPCC TAR, Ch. 1)

20. The Climate System (IPCC TAR, Ch. 1)

21. The Climate System Three important controling factors: • Latitude - insolation • Elevation - temp. decrease with height • Closeness to oceans - heat reservoir

22. The Climate System Water in the climate system: (Peixoto & Oort, 1992)

23. The Climate System

24. The Climate System Mean extreme temperatures and differences (˚C) :

25. Thermal Inertia of Oceans Annual Temperature Range (Wallace & Hobbs, 1979)

26. The Climate System (Michael Pidwirny, DLESE, 2004)

27. The Climate System Subsystems • Atmosphere - rapid changes • - links other subsystems • - greenhouse gases • Ocean • slow evolution (“memory”, “flywheel”) • chemical role, esp. CO2 • Land • - range of time scales • - cryosphere & biosphere roles • - location of continents

28. Cryosphere Note: Time scales, albedo effects

29. Biosphere Note: albedo, evapotranspiration, surface roughness, gas exchanges (esp. CO2)

30. Feedbacks Internal couplings through linking processes Amplify or diminish initial induced climate change

31. Negative Feedback: Example How does Earth’s temperature get established and maintained?

32. Solar Constant At photosphere surface, solar flux ~ 6.2.107 W-m-2

33. Solar Constant At photosphere surface, solar flux ~ 6.2.107 W-m-2 At Earth’s orbit, solar flux ~ 1360 W-m-2

34. Planetary Albedo Scattering: air molecules, aerosols Reflection: clouds Surface albedo

35. What is Earth’s temperature? Balance: Radiation in = Radiation out a Incoming = 1360 W-m-2 x (1-albedo) x (area facing sun) = 1360 x (1-0.3) x pa2 = 1.2.10+17 W

36. What is Earth’s temperature? Balance: Radiation in = Radiation out a Incoming = 1360 W-m-2 x (1-albedo) x (area facing sun) = 1360 x (1-0.3) x pa2 = 1.2.10+17 W Outgoing = sT4 x (area emitting) ; i.e., black body = sT4 x 4 pa2

37. What is Earth’s temperature? Balance: Radiation in = Radiation out a Incoming = 1360 W-m-2 x (1-albedo) x (area facing sun) = 1360 x (1-0.3) x pa2 = 1.2.10+17 W Outgoing = sT4 x (area emitting) ; (i.e., black body) = sT4 x 4 pa2 Balance implies T = {0.7(1360 W-m-2)/4s}1/4 = 255 K = -18 oC

38. What is Earth’s temperature? Balance: Radiation in = Radiation out a Balance implies T = -18 oC Observed surface T = +15 oC Difference? Must account for atmosphere (greenhouse effect).

39. What if temperature decreases? a The same: Incoming = 1.2.10+17 W Outgoing = sT4 x (area emitting) = sT4 x 4 pa2

40. What if temperature decreases? a These are the same: Incoming = 1.2.10+17 W Outgoing = sT4 x (area emitting) = sT4 x 4 pa2 • But for T < 255 K: • imbalance • Incoming solar exceeds outgoing IR • net energy input • T increases ~ Negative Feedback ~

41. Negative Feedback Perturb climate system Negative feedback moves climate back toward starting point A stabilizing factor

42. Positive Feedback: Example How does Earth’s temperature get established and maintained?

43. Greenhouse Effect IR radiation absorbed & re-emitted, partially toward surface Solar radiation penetrates

44. Greenhouse Effect IR radiation absorbed & re-emitted, partially toward surface Net IR: ~25-100 W-m Emitted IR: ~200-500 W-m

45. Greenhouse Effect Cooler atmosphere: - Less water vapor - Less IR radiation absorbed & re-emitted Solar radiation penetrates

46. Greenhouse Effect Cooler atmosphere: - thus less surface warming - cooler surface temperature Solar radiation penetrates

47. Positive Feedback Perturb climate system Positive feedback moves climate away from starting point A destabilizing factor Other examples (textbook): - ice-albedo feedback - CO2-ocean temperature feedback

48. Feedbacks Distinguish between: 1. external forcing change - e.g., insolation, volcanism - often predictable 2. Internal feedback mechanisms - nonlinear, coupled interactions - generally less predictable (stochastic)

49. Radiation Spectrum Black Body Curves Emission 255 K 6,000 K Wavelength [m] Solar (shortwave, visible) Terrestrial (longwave, infrared)

50. Daily Solar Radiation at Top of Atmos. [106 J-m-2]