Introduction. Introduction. Introduction. Outline Last IPCC report : 2001 Last IPCC report :

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1 Introduction Greenhouse Gases & Climate Change Laurent Bopp LSCE, Paris When did the story start? ¾1827 Fourier hypothesizes greenhouse effect ¾1860 Tyndal identifies CO2 and water vapor as heat trapping gases ¾1896 Arrenhius calculates earth warming from gases Or «How do we go from a GreenHouse to and predicts future warming from doubling CO2 "On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground" Philosophical Magazine 41, 237 (1896) - a changing climate» Introduction ¾1980s Ice core data (here from Vostok) reveal a large correlation between Temperature and Atmospheric Composition Introduction ¾1958 Keeling begins direct measurement of CO2 in atmosphere

2 Introduction 2001 Last IPCC report : An increasing body of observations gives a collective picture of a warming world and other changes in the climate system Introduction 2001 Last IPCC report : An increasing body of observations gives a collective picture of a warming world and other changes in the climate system Emissions of greenhouse gases ( ) due to human activities continue to alter the atmosphere in ways that are expected to affect the climate Introduction Outline 2001 Last IPCC report : An increasing body of observations gives a collective picture of a warming world and other changes in the climate system Emissions of greenhouse gases ( ) due to human activities continue to alter the atmosphere in ways that are expected to affect the climate There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities 1. Earth s radiative budget : The importance of the GreenHouse Effect 2. GHG : Species, Sources and Sinks, Recent evolution and projections 3. Response of Climate : observations, projections

3 1. Earth s radiative budget 1.1 Emission of radiation by a solid body or a gaz 1. Earth s radiative budget No spectral overlap between predicted spectra with temperatures similar to sun and earth Planck s Law : F 2 5 2πc hλ λ, T ) = ch kλt e 1 B ( / (monochromatic emissive power of a black body) Wien s Law : λ max ( T ) = 2897 /T Wavelength of maximum intensity with T Stefan-Boltzmann s Law : 4 F B = σt hot bodies radiate more energy than cold ones Peak at 15 µm Peak at 0.5 µm Observations 1. Earth s radiative budget Version 1 : Without any atmosphere S 0 αs 0 F e 1. Earth s radiative budget 1.2 Absorption of radiation by gases The mechanism of absorption differs depending on the the wavelength (1-α) S 0 = σ T e 4 S 0 = 342 W m -2 Albedo α = 0.3 Stephan-Boltzman Constant σ = W m -2 K -4 UltraViolet Molecule Dissociation InfraRed Molecule Vibration MicroWave Molecule Turning Te = 255 K! It is too cold

4 1. Earth s radiative budget 1.2 Absorption of radiation by gases Some greenhouse gases transmission spectra - di-atomic molecules (O2, N2) do not absorb IR radiation (no electric dipole moment) -Tri-atomic molecules (H2O, CO2, N2O, CH4, ) present different forms of vibration and thus absorb at different wavelength An example : the CO 2 molecule 4.2 µm 15 µm CO2 Absorption Spectrum : 2 absorbing bands at 4.2 micron (B mode) and 15.0 micron (C and D mode) 1. Earth s radiative budget 1.3 Greenhouse Principle Absorbing Spectrum : - almost complete in UV - very low in the visible and near IR - IR : mainly H2O except in the 7-15 micron band

5 1. Earth s radiative budget 1.3 Greenhouse Principle Radiation emitted to space 1. Earth s radiative budget Version 2 : With an atmosphere (only one layer here ) Altitude S 0 αs 0 τf e F a GHG F e F a Absorption - emission by gases Transparent atmosphere in SW Partially absorbing in IR Surface : (1-α) S 0 + F a = F e Top of the Atmosphere : F e -F a = τf e +F a Emission Temperature Surface Temperature Temperature Emitted Radiation from the surface 1. Earth s radiative budget 1.4 The Earth s annual and global mean energy balance. 2. Greenhouse Gases (GHG) Sinks : Mainly chemical processes - reaction with OH in troposphere (CH4, HFCs, HSFCs..) - photolysis in stratosphere and mesosphere (N2O, PCFs, CFCs, ) Greenhouse Gas Mean Concentration / Burden Repartition Radiative Properties (RF, GWP) Recent Evolution Sources (Natural and Artificial): Mainly at the surface IPCC, 2001

6 2. Greenhouse Gases (GHG) 2.1 Useful definitions Life time : Atmospheric burden divided by mean global sink for a gas in steady state. Characterizes time to turn over atmospheric burden once. Radiative Forcing (RF): Change in net radiative flux at the tropopause due to a perturbation of the climate system (e.g. GHG concentrations) after allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures held fixed at the unperturbed values GWP (Global Warming Potential) : ratio of the time-integrated forcing from the instantaneous release of 1 kg of trace substance relative to 1 kg of a reference gas (usually CO2). GWP is function of the radiative properties and life time of the considered gas but also of the time period considered. 2. Greenhouse Gases (GHG) Gas 2.2 Main Greenhouse gases (Pre-Industrial) LifeTime Concentration (ppm) H 2 O few days CO yr Ozone O 3 variable Methane CH yrs Oxide Nitreux N 2 O yrs Natural Greenhouse Effect (W/m2) Climate Sensitivity : Perturbation to equilibrium surface temperature Ts is related to radiative forcing by Ts = λ RF Contribution to Natural Greenhouse Effect 2. Greenhouse Gases (GHG) 2.2 Main Greenhouse gases (from pre-industrial to today) - Hydrofluorocarbons - Chlorofluorocarbons - Increase from 1750 CO 2 : +31 % CH 4 : +151 % N 2 O : +17 % O 3 trop. : +36 % IPCC, 2001

7 2. Greenhouse Gases (GHG) Global Warming Potential Lifetime Global Warming Potential (Time Horizon in Years) GAS (years) 20 yrs 100 yrs 500 Carbon Dioxide CO Methane CH Nitrous Oxide N 2 O CHLOROFLUOROCARBONS CFC CFC CFC HYDROFLUOROCARBONS HFC-23 CHF HFC-32 CH 2 F HFC-41 CH 3 F HFC-125 CHF 2 CF HFC-134 CHF 2 CHF HFC-143 CHF 2 CH 2 F HFC-152 CH 2 FCH 2 F HFC-161 CH 3 CH 2 F HFC-227 CF 3 CHFCF Main Greenhouse gases IPCC (2001) classifies the different GHGs in -CO2 - non-co2 Kyoto Gases - CH4 -N2O - HFCs (hydrofluorocarbons) - PFCs (perfluorocarbons) and SF6 (sulphur hexafluoride) - Montreal Protocole Gases CFCs, halons - Tropospheric O3 - Non-direct GHGs -CO -NOx.. Contribution to Anthropogenic Greenhouse effect 2. Greenhouse Gases (GHG) 2.3 Example : CH4 cycle Second GHG in terms of contribution to anthropogenic grenhouse effect But also Controls amount of OH (hydroxyl) in the troposphere Affects concentrations of water vapor and O 3 (ozone) in the stratosphere and plays a key-role in conversion of reactive Cl to less reactive HCl in stratosphere But large uncertainties on H2O forcing. IPCC, 2001

8 2. Greenhouse Gases (GHG) 2.3 Example : CH4 cycle (From 750 ppb to 1745 ppb in 1998) 2. Greenhouse Gases (GHG) 2.3 Example : CH4 cycle Natural Sources (~200 TgC/yr) : Anthropogenic Sources (~ 400 TgC/yr) : Sinks (~576 TgC/yr) : Soils Tropospheric OH Stratospheric Loss Wetlands Wild ruminants Termites Agriculture (Rice) Ruminants Waste treatment FF burning Biomass burning Ocean Hydrates 2. Greenhouse Gases (GHG) 2. Greenhouse Gases 2.3 Example : CH4 cycle - Life time : t = 8.4 yr (IPCC, 2001) with a burden of 4850 TgCH4 ansd a sink of 576 TgCH4/yr But complex feedback on OH concentration. 2.4 Projections under different scenarios - Some sources poorly constrained and potential feedbacks of GW on some of those sources (hydrates?) IPCC 2001

9 3. Response of Climate? 3.1 Recent observations (from IPCC 2001) - Sea surface temperature : + 0,8ºC (± 0,2) from begining of XXth century 3.1 Observations 3.2 A Cause-Effect relationship? 3.3 Projections - Confirmed by others instruments (balloons, satellites..) Recent Warming compared to past 1000 y reconstruction But Warming is not uniform in time and space

10 World Mountain Glaciers Sea Level evolution - from maregraphs Le glacier d Argentière (Alpes) - mechanisms : water thermal expansion + contribution from greenland melting Precipitations Number of frost days and Heat Wave duration (IPCC, 2001) Frost Days Heat Waves - Mid to high latitudes from N.H. : increase (+0,5/1%/decade) - sub-tropics (10N-30N) : decrease (-0.3%/decade)

11 An increasing body of observations gives a collective picture of a warming world and other changes in the climate system 3.2 A cause-effect relationship? Historical Radiative Forcing IPCC,2001 Climate Models U + 2Ω U =. t There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities - from climate models - New detection techniques

12 3.3 Projections Temperature Change ( C) IPCC, 2001 And a new glaciation very unlikely

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