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Climate change: certainties and uncertainties

Climate change: certainties and uncertainties. Hervé Le Treut, Laboratoire de Météorologie Dynamique (CNRS/Ecole Normale Supérieure/Ecole Polytechnique/ Université Paris 6) Académie des sciences. Plan of the talk. 1. The main greenhouse gases

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Climate change: certainties and uncertainties

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  1. Climate change: certainties and uncertainties Hervé Le Treut, Laboratoire de Météorologie Dynamique (CNRS/Ecole Normale Supérieure/Ecole Polytechnique/ Université Paris 6) Académie des sciences

  2. Plan of the talk • 1. The main greenhouse gases The emission by human activities: recent evolution The time scales in question: are the past climate variations relevant indicators? How do atmospheric chemical changes affect the Earth radiative budget? • 2. Consequences What is already detectable? How can we predict future evolutions? Models and scenarios. What are the forecasts for the coming century?

  3. During the last century, the atmospheric composition has undergone changes which are unprecedented over the last millenia IPCC, 2001

  4. The yearly use of energy (and associated CO2 emissions) have increased sharply since the second world war, with a direct impact on CO2 concentration. Schilling & al + Observatoire énergie + AIE, cited by Jancovici

  5. 100 millions years = 100 000 millenia G. Jacques, communication personnelle

  6. Louis Agassiz

  7. Quaternary evolution follows slow patterns of evolution Milankovitch Obliquity: ~ 40 000 years Eccentricity: ~ 100 000 years Precession of the equinoxes: ~ 21 000 years Illustrations de S. Joussaume (éditions du CNRS,1993)

  8. The rate of current changes is large when compared with observed evolutions over the Quaternary era. GIEC, 20001 (CNRS/CEA)

  9. Changes of global temperature over the last millenium are within a few tenths of a degree Mann, IPCC, 2001

  10. Changes in the atmospheric composition act on complex and interactive systems which had previously reached equilibrium:

  11. First example of a complex system: the global carbon cycle GIEC, 1990 - CDIAC

  12. CO2 emissions per habitant 1 2 0.5

  13. Greenhouse emission per kg of produced food (in France) Jancovici, 2002

  14. Greenhouse gas emission per passenger and kilometer (in France) Jancovici, 2002

  15. Methane sources in millions of tons per year

  16. OH Pollution: brings CH4 Pollution: brings O3

  17. Another example of a complex system: the energy cycle GIEC, 2001

  18. Atmospheric constituents contributing to the greenhouse effect Anthropogenic(2.8 W/m2) Natural (155 W/m2)

  19. Evolution of the greenhouse effect after some instantaneous emission of one ton Forçage radiatif par tonne émise Année après la perturbation Hauglustaine D., LSCE

  20. Greenhouse Gas Time scale (years) GWP (20 years) GWP (50 years) GWP (100 years) CO2 150 1 1 1 CH4 12 62 23 7 N2O 114 275 296 156 CFC-11 45 6 300 4 600 1 600 CFC-12 100 10 200 10 600 5 200 HCFC-22 12 4 800 1 700 540 HFC-134a 14 3 300 1 300 400 CF4 50 000 3 900 5 700 8 900 SF6 3 200 15 100 22 200 32 400 Greenhouse Warming Potential

  21. Radiative forcing of anthropogenic elements (1750 à 2000) IPCC [2001]

  22. Agence Européenne pour l’Environnement

  23. Are consequences already perceptible ? Mann, IPCC, 2001

  24. Change in the extension of mountain glaciers IPCC, 2001

  25. Climate modelling: an old dream which became possible in the last decadesRichardson (1922) An artist view of recent climate models (L. Fairhead /LMD-CNRS) The weather machine

  26. The real world (synthetic radar image)

  27. The « simulated planets » are now very similar to the real one Simulation carried out using the Japanese Earth Simulator, JSTEC

  28. Earth simulator

  29. Atmosphere and ocean: two fluids which act as partners

  30. IPSLCM4 Increasingly complex models: The IPSL-CM4 Earth System Model Continents Atmosphere Oceans Orchid é e LMD ZT LMD ORCALIM Z Physics Atmospheric circulation Ocean circulation Land Surface Sea ice Soil and vegetation STOMATE PISCES Terrestrialbiogeochemistry Marine biologyand biogeochemistry CarbonCycle Carbon CO2 Carbon INCA Chemistry CH , VOCs, DMS 4 Gases Chemistry Aerosols Nutrients & Aerosols Salt Aerosols

  31. Clouds simulated by models in 1990 … and in 2000

  32. Model evaluation: precipitations

  33. IPCC scenarios: a wide range of possible futures (without taking into account specific policies, such as those linked with Kyoto protocol)

  34. Surface air temperature IPSL-CM4 coupled model A2 Without sulf. aerosol A2 A1B B1 Comit. Control

  35. IPCC 2001 Report • Changes in global mean temperature:

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