Transcript IPCC [2001]
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 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? During the last century, the atmospheric composition has undergone changes which are unprecedented over the last millenia IPCC, 2001 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 100 millions years = 100 000 millenia G. Jacques, communication personnelle Louis Agassiz 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 ) The rate of current changes is large when compared with observed evolutions over the Quaternary era. GIEC, 20001 (CNRS/CEA) Changes of global temperature over the last millenium are within a few tenths of a degree Mann, IPCC, 2001 Changes in the atmospheric composition act on complex and interactive systems which had previously reached equilibrium: First example of a complex system: the global carbon cycle GIEC, 1990 - CDIAC CO2 emissions per habitant Inde Emission de CO 2 par habitant Cuba Mexique Chili Venezuela Afrique du Sud Corée du Sud Chine Pays Ukraine France Italie Royaume Uni Japon Allemagne Belgique Australie Canada USA 0,00 5,00 0.5 1 10,00 2 15,00 tonne par habitant 20,00 25,00 Greenhouse emission Emissions per kg of de produced (in France) GES parfood kg d'aliment Veau Mouton Boeuf Beurre Fromage pâte cuite Fromage pâte crue Cochon Poulet fermier Oeufs Farine Lait de vache 0 2 4 6 kg C Jancovici, 2002 8 10 12 Greenhouse gas emission per passenger and kilometer (in France) Avion (court courrier) Mode de transport Voiture (ville) Avion (long courrier) Voiture (route) Bus Train RU Train SNCF 0 20 40 60 80 Emissions, gC par passager.km Jancovici, 2002 100 120 Methane sources in millions of tons per year 250 swamps, rice termits ocean hydrates energy litter, wate cows biomass 200 150 100 50 0 natural anthropogenic OH Pollution: brings CH4 Pollution: brings O3 Another example of a complex system: the energy cycle GIEC, 2001 Atmospheric constituents contributing to the greenhouse effect Halocarbons 12% Water vapor 55% Other greenhouse gases 30% Clouds 15% Natural (155 W/m2) Ozone 13% CO2 53% N2O 5% CH4 17% Anthropogenic (2.8 W/m2) Forçage radiatif par tonne émise Evolution of the greenhouse effect after some instantaneous emission of one ton Année après la perturbation Hauglustaine D., LSCE Greenhouse Warming Potential Greenhouse Gas CO2 CH4 N2O CFC-11 CFC-12 HCFC-22 HFC-134a CF4 SF6 Time scale (years) GWP (20 years) GWP (50 years) GWP (100 years) 150 12 114 45 100 12 14 50 000 3 200 1 62 275 6 300 10 200 4 800 3 300 3 900 15 100 1 23 296 4 600 10 600 1 700 1 300 5 700 22 200 1 7 156 1 600 5 200 540 400 8 900 32 400 Radiative forcing of anthropogenic elements (1750 à 2000) IPCC [2001] Agence Européenne pour l’Environnement Are consequences already perceptible ? Mann, IPCC, 2001 Change in the extension of mountain glaciers IPCC, 2001 Climate modelling: an old dream which became possible in the last decades Richardson (1922) The weather machine An artist view of recent climate models (L. Fairhead /LMD-CNRS) The real world (synthetic radar image) The « simulated planets » are now very similar to the real one Simulation carried out using the Japanese Earth Simulator, JSTEC Earth simulator Atmosphere and ocean: two fluids which act as partners Increasingly complex models: The IPSL-CM4 Earth System Model IPSLCM4 Continents Atmosphere Orchidée Physics LMDZT LMDZ Land Surface Soil and vegetation Atmospheric circulation STOMATE Terrestrial biogeochemistry Carbon Cycle Carbon CH4, ORCALIM Ocean circulation Sea ice PISCES Marine biology and biogeochemistry CO2 INCA Chemistry Oceans VOCs, Aerosols Carbon Chemistry Gases DMS Nutrients & Aerosols Aerosols Salt Clouds simulated by models in 1990 … and in 2000 Model evaluation: precipitations IPCC scenarios: a wide range of possible futures (without taking into account specific policies, such as those linked with Kyoto protocol) Surface air temperature IPSL-CM4 coupled model A2 Without sulf. aerosol A2 A1B B1 Comit. Control IPCC 2001 Report • Changes in global mean temperature: Unmodified for the last 20 years Geographical disparities Climate change for two models and two scenarios: Temperature CNRM A2 B1 IPSL Climate change with two models : Precipitations CNRM A2 IPSL Agreement between models is scale dependent CMIP models Oceans: Are changes irreversible? IPCC, 2001 Gordon (86) Changes in sea level: A delayed effect IPCC, 2001 Will the moderation effect of vegetation last for a long time? Will vegetation continue to mitigate the atmospheric increase of carbon dioxide? . CO2 absorption with climate change Without climate change Difference of the two Other risks are not well diagnosed: Greenland melting, methane from permafrost … Regional approaches: PRUDENCE changes in summer precipitations Prudence EU project Conclusions • Climate change will constitute one of the important sources of tension affecting the Earth during the century to come. • A certain level of climate change is now unavoidable; the global amplitude of these changes, their rate, the nature of their impacts, however, depend on our ability to curve down greenhouse gases emissions • The risks resulting from our unability to predict the details of future climate changes, the possibility of thresholds above which changes may be amplified, reinforce the need for immediate actions