1. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The modelling of the climate system Professor Lennart Bengtsson ESSC, University of Reading Max-Planck-Institut für Meteorologie, Hamburg

2. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

3. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Temperature change 1854 - 2004 ( land areas only)

4. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Temperature change 1854 - 1904 ( land areas only)

5. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Temperature change 1904 - 1954 ( land areas only)

6. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Temperature change 1954 - 2004 ( land areas only)

7. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Temperature change 1954 - 2004

8. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The modelling of the climate system What is climate? Climate variations on different time-scales The modelling of climate Atmospheric modelling and weather prediction Modelling of the Earth climate system How predictable is climate? Model simulation of the present climate Why is the climate changing? Climate change prediction Concluding remarks

9. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The classical view on climate Climate as a stationary concept

10. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Köppen climate zones Main groups A: Tropical rainy climate, all months > +18 C B: Dry climate, Evaporation > Precipitation C: Mild humid climate, coldest month +18 C - -3 C D: Snowy - forest climate, coldest month +10 E: Polar climate, warmest month < +10 C ET: Tundra climate, warmest month > 0 C Subgroups f : Moist, no dry seasons w: Dry season in winter s : Dry season in summer

11. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity GPCP (Prec) CRU2 (Temp) ECHAM5 T159 Köppen climate zones

12. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity What is climate? Climate is nowadays generally defined as a comprehensive statistical description of weather ( including extremes) over a sufficiently long period of time (30-100 years) There is no sharp distinction between weather and climate There are free atmospheric modes of circulation that have time-scales of up to about two years ( quasi-biennal oscillation) There are coupled ocean-atmospheric modes that have time-scales from weeks to several decades. A dominant feature is the El-Nino phenomenon in the eastern tropical Pacific ocean with a time-scale of about four years.

13. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The present view on climate Climate as a dynamical system

14. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Climate variations on different time-scales Climate variations are dominated by chaotic weather events Other variations are due to coupled ocean-atmosphere processes which could cover longer periods of time. They are probably also mainly chaotic. Climate would also vary due to changes in solar irradiation( regular or otherwise) and under the influence of volcanic aerosols Climate also varies due to changes in the composition of the atmosphere such as greenhouse gases and aerosols

15. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Shorter term climate variations and their likely causes

16. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Natural temperature variations ENSO influence

17. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

18. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Natural temperature variations Pinatubo and ENSO

19. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

20. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The modelling of climate Prior to the 1950s climate was essentially a descriptive science, but general ideas of the general circulation of the atmosphere and the oceans existed Over the past 50 years the direction of climate research has changed driven by space based observations and mathematical modelling of the climate system. Climate modelling has occurred along three lines: - increased numerical resolution and more accurate treatment of individual physical and chemical processes - coupling of individual model components of the climate into Earth system models including aspects of the biosphere - ensemble predictions to be able to separate signal from noise.

21. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity What is a CLIMATE MODEL? A COMPUTER PROGRAM which numerically solves the MATHEMATICAL EQUATIONS that represent the LAWS OF PHYSICS. Components include the: ATMOSPHERE, OCEAN, LAND, CRYOSPHERE and BIOSPHERE and all the dynamics, physical processes and interactions between them. The most comprehensive climate models include: GENERAL CIRCULATION MODELS (GCMs) as atmospheric and oceanic components. An AGCM follows the evolution of all the weather systems, clouds, and rain, and the interactions with the land and ocean.

22. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Climate system in pictorial form

23. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

24. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Climate system as a principle system

25. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Climate model components

26. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The strategy of climate research

27. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Significant atmospheric processes

28. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Aspects of numerics & physical parameterizations for AGCMs

29. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Resolution issues

30. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Modelling error as a function of horisontal and vertical resolution (ECHAM climate model 2005)

31. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity How well can model simulate present climate? Some examples

32. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Typical cyclone storm tracks Tracks Intensities

33. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Storm track density ERA40 (left, 1979 - 2002) ECHAM5 ( right, 1979 - 1999, atmos. model run) for the relative vorticity at 850 mb

34. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Number of extra-tropical storms at the Northern Hemisphere as a function of intensity during winter

35. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

36. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity ECHAM5 simulated ERA40 determined from analyses. Köppen climate zones

37. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity How predictable is climate? Do we have a unique climate? Predictability of weather and predictability of climate

38. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity CLIMATE PREDICTION AND CHAOS “ For want of a nail, the shoe was lost; For want of a shoe, the horse was lost; For want of a horse, the rider was lost; For want of a rider, the battle was lost; For want of a battle, the kingdom was lost “

39. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Predictability of weather

40. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity ECMWF EPS: Forecast Started 8 th January 00UTC

41. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity ECMWF EPS: Forecast Started 6 th January 00UTC

42. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Predictability of snow in Germany

43. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Why is the climate changing? There are natural changes on a variety of time scales. Some of these changes are chaotic and unpredictable. Sometimes chaotic events are inadvertently interpreted as due to specific external events ( e.g. solar forcing, volcanic eruptions, human influences etc.). However, increasing greenhouse gases exercise a real influence on climate and observations and model results are supporting each other

44. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The greenhouse effect

45. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The greenhouse effect

46. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Carbon dioxide increase 1957-2003

47. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity CO 2 and CH 4 Concentrations Past, Present and Future Compiled by K. Alverson

48. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Svante Arrhenius 1859-1927

49. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The carbon cycle

50. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

51. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

52. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Annual increase in GHG forcing 1958-2003

53. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The problem of climate change prediction How credible are climate change predictions? How will climate forcing change? What aspects of climate change is predictable? What is unpredictable? Some important processes are not yet generally considered in climate models. This include feedback with the biosphere

54. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Climate feedback

55. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The feedback problem

56. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The feedback problem

57. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity The feedback problem

58. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Feedback results from different models

59. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Delworth and Knutson, 2000 Monte-Carlo simulations with a coupled AO GCM: one out five simulations almost perfectly reproduced the observed global temperature variability. obsexp 3

60. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Ensemble climate trends averaged for different time-periods (T/decade) 1-30 years 1-80 years

61. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

62. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Storm track density difference between scenario A1B ( aver. cond. 2071-2100 and ( aver. cond. 1961-1990) for the ECHAM 5 model. NH left and SH right. Note the poleward change of the storm track at the SH

63. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Coupled Model T63L31

64. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity

65. 16 January 2005 Lennart Bengtsson Celsius lecture 2005 Uppsala Unversity Concluding remarks Climate model can reproduce most features of the general circulation of the atmosphere( and to a lesser degree) of the oceans. Results generally improves with higher numerical accuracy (resolution) The treatment of small scale physical processes, turbulence, clouds, boundary layer fluxes etc. are parameterised ( only expressed in terms of the resolvable parameters) and thus to some extent subject to ad hoc assumptions. However climate change feedbacks are likely to be influenced by such assumptions Climate change predictions over larger areas and longer time-scales are dynamically robust (albeit model dependent). Regional climate change predictions of a few decades and shorter are most likely unpredictable, but an ensemble over many cases could indicate a change in the overall probability distribution of climate and weather events.