climate change: certainties and uncertainties
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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 - PowerPoint PPT PresentationTRANSCRIPT
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
Eccentricity:~ 100 000 years
Precession of the equinoxes:~ 21 000 years
Obliquity:~ 40 000 years
MilankovitchQuaternary evolution follows slow patterns of evolution
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
Emission de CO2 par habitant
USA
Canada
Australie
Belgique
Allemagne
Japon
Royaume Uni
Italie
France
Ukraine
Chine
Corée du Sud
Afrique du Sud
Venezuela
Chili
Mexique
Cuba
Inde
0,00 5,00 10,00 15,00 20,00 25,00
Pays
tonne par habitant
COCO2 2 emissions per habitant emissions per habitant
0.5 1 2
Emissions de GES par kg d'aliment
0 2 4 6 8 10 12
Lait de vache
Farine
Oeufs
Poulet fermier
Cochon
Fromage pâte crue
Fromage pâte cuite
Beurre
Boeuf
Mouton
Veau
kg C
Greenhouse emission per kg of produced food (in France)Greenhouse emission per kg of produced food (in France)
Jancovici, 2002Jancovici, 2002
0 20 40 60 80 100 120
Train SNCF
Train RU
Bus
Voiture (route)
Avion (long courrier)
Voiture (ville)
Avion (court courrier)
Mo
de
de
tran
spo
rt
Emissions, gC par passager.km
Jancovici, 2002Jancovici, 2002
Greenhouse gas emission per passenger and kilometer (in France)Greenhouse gas emission per passenger and kilometer (in France)
0
50
100
150
200
250
natural anthropogenic
swamps, rice
termits
ocean
hydrates
energy
litter, wate
cows
biomass
Methane sources in millions of tons per year
Pollution:brings
Pollution: brings CH4OH
O3
Another example of a complex system: the energy cycle
GIEC, 2001
Other greenhouse
gases30%
Clouds15%
Water vapor55%
Atmospheric constituents contributing to the greenhouse effect
NaturalNatural
(155 W/m(155 W/m22))
CH4
17%
Halocarbons12%
Ozone13%
N2O5%
CO2
53%
AnthropogenicAnthropogenic
(2.8 W/m(2.8 W/m22))
Forç
ag
e r
ad
iati
f p
ar
ton
ne é
mis
eForç
ag
e r
ad
iati
f p
ar
ton
ne é
mis
e
Evolution of the greenhouse effect after Evolution of the greenhouse effect after some instantaneous emission of one ton some instantaneous emission of one ton
Année après la perturbationAnnée après la perturbation
Hauglustaine D., LSCEHauglustaine D., LSCE
Greenhouse Warming Potential
8 9005 7003 90050 000CF4
5401 7004 80012HCFC-22
4001 3003 30014HFC-134a
32 40022 20015 1003 200SF6
156296275114N2O
1 600 4 6006 30045CFC-11
5 20010 60010 200100CFC-12
7236212CH4
111150 CO2
GWP (100 years)
GWP (50 years)GWP (20 years)Time scale (years)
Greenhouse Gas
Radiative forcing of anthropogenic elements (1750 à 2000)
IPCC [2001]
Agence Européenne pour Agence Européenne pour l’Environnementl’Environnement
Are consequences already perceptible ?
Mann, IPCC, 2001
IPCC, 2001
Change in the extension of mountainglaciers
Climate modelling: an old dream which became possible in the last decades
Richardson (1922)
The weather machineAn 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
Physics
CarbonCycle
Chemistry
Continents Atmosphere OceansIPSLCM4
Atmosphericcirculation
Ocean circulation Sea ice
Carbon
DMS
Nutrients
ChemistryGases
&
Aerosols
CO2
Land Surface
Soil and vegetation
LMDZ
Orchidée LMDZT
ORCALIM
INCA
STOMATE PISCES
Carbon
CH4, VOCs,
Aerosols
Aerosols
Marine biologyand biogeochemistry
Terrestrialbiogeochemistry
Salt
Clouds simulated by models in 1990
… and in 2000
Model evaluation: precipitations
IPCC scenarios: a wide range ofpossible futures(without taking into account specific policies, such as those
linked with Kyoto protocol)
Surface air temperature
Comit.
IPSL-CM4 coupled model
A1BA2
Control
A2 Without sulf. aerosol
B1
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
A2
B1
CNRM IPSL
Climate change with two models : Precipitations
A2
CNRM
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 absorptionwith climate change
Without climatechange
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