When did the story start ?
1827 Fourier hypothesizes greenhouse effect
Introduction
1860 Tyndal identifies CO2 and water vapor as heat trapping gases
1896 Arrenhius calculates earth warming from gases
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)
-
1980s Ice core data (here from Vostok) reveal a large correlation between Temperature and Atmospheric Composition
Introduction
EPICA Dome C: up to -800 kyr
Introduction
Adapted from Lüthi et al. 2008, Loulergue et al. 2008, and Schilt et al. 2010
2007 Last IPCC report :
Introduction
“Global atmospheric concentrations of
carbon dioxide, methane and nitrous
oxide have increased markedly as a
result of human activities since 1750 and
now far exceed pre-industrial values
determined from ice cores spanning
many thousands of years
2007 Last IPCC report :
“
Warming of the climate system
is unequivocal, as is now evident
from observations of increases in
global average air and ocean
temperatures, widespread melting
of snow and ice, and rising
global average sea level.”
Introduction
“Global atmospheric
concentrations of carbon dioxide,
methane and nitrous oxide have
increased markedly as a result of
human activities since 1750 and
now far exceed pre-industrial
values determined from ice cores
spanning many thousands of
years
2001 IPCC report :
“Emissions of greenhouse gases (…) due to human activities continue to
alter the atmosphere in ways that are expected to affect the climate”
“An increasing body of observations gives a collective picture of a warming world and other changes in the climate system”
Introduction
“There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities”
2007 Last IPCC report :
Introduction
“Most of the observed increase in global average temperatures
since the mid-20th century is very likely due to the observed
increase in anthropogenic greenhouse gas concentrations.
This is an advance since the TAR’s conclusion that “most of
the observed warming over the last 50 years is likely to have been
due to the increase in greenhouse gas concentrations”.
Discernible human influences now extend to other aspects of
climate, including ocean warming, continental-average
temperatures, temperature extremes and wind patterns.
Likely : > 66 %
Very likely : > 90%
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
Outline
1. Earth’s radiative budget
1.1 Emission of radiation by a solid body or a gaz
Planck’s Law : 1
2),(
/
52
TkchBe
hcTF
(monochromatic emissive power of a black body)
Wien’s Law : Wavelength of maximum intensity with T TT /2897)(max
Stefan-Boltzmann’s Law : hot bodies radiate more energy
than cold ones
4TFB
1. Earth’s radiative budget
No spectral overlap between predicted spectra with temperatures similar to sun and earth
Observations Peak at 0.5 mm
Peak at 15 mm
1. Earth’s radiative budget
Version 1 : Without any atmosphere
Fe S0 S0
(1-) S0 = Te4
S0 = 342 W m-2
Albedo 0.3
Stephan-Boltzman Constant = 5.67 10-8 W m-2 K-4
Te = 255 K ! It is too cold…
1. Earth’s radiative budget
1.2 Absorption of radiation by gases
The mechanism of absorption differs depending on the the wavelength
UltraViolet
Molecule Dissociation
InfraRed
Molecule Vibration
MicroWave
Molecule Turning
1. Earth’s radiative budget
1.2 Absorption of radiation by gases
- 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 CO2 molecule
CO2 Absorption Spectrum : 2 absorbing bands at 4.2 micron (B mode) and
15.0 micron (C and D mode)
4.2 mm
15 mm
Absorbing Spectrum :
- almost complete in UV
- very low in the visible and near IR
- IR : mainly H2O except in the 7-15
micron band
Emission Temperature Surface
Temperature
Radiation emitted to space
Emitted Radiation from the surface
Absorption - emission by
gases
Temperature
Alt
itu
de
1. Earth’s radiative budget
1.3 Greenhouse Principle
1. Earth’s radiative budget
Surface : (1-) S0 + Fa = Fe
Top of the Atmosphere : Fe - Fa = Fe + Fa
Fe S0 S0
Fe
Fa
Fa
Transparent atmosphere in SW
Partially absorbing in IR
GHG
Version 2 : With an atmosphere (only one layer here…)
2. Greenhouse Gases (GHG)
Atmospheric concentrations vary by more than eight orders of
magnitude
Radiative efficiencies vary by more than four orders of
magnitude,
enormous diversity in their properties and origins.
2. Greenhouse Gases (GHG)
Greenhouse Gas Mean Concentration / Burden
Repartition
Radiative Properties (RF, GWP)
Recent Evolution
Sources (Natural and Artificial): Mainly at the surface
Sinks : Mainly chemical processes
- reaction with OH in troposphere (CH4, HFCs, HSFCs..)
- photolysis in stratosphere and mesosphere (N2O, PCFs, CFCs, …)
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.
CH4 : Atm. Burden : 1,774 ± 1.8 ppb
Sinks (mostly tropospheric oxydation with OH) 581 Tg(CH4)
12 years
N2O : Atm. Burden : 319 ± 0.12 ppb
Sink (mostly photolysis in the strat.): 12.5 TgN
114 years
CO2 : 5 yrs ? … 200 yrs ?… to be discussed tomorrow…
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
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
Climate Sensitivity : Perturbation to equilibrium surface temperature Ts is related
to radiative forcing by DTs = RF
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
Climate Sensitivity : Perturbation to equilibrium surface temperature Ts is related
to radiative forcing by DTs = RF
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.
H2O few days 0-1000 100
CO2 ??? 280 50
Ozone O3 variable 0.03 1.7
Methane CH4 8-12 yrs 0.5 1.3
Nitrous Oxide N2O 100-200 yrs 0.28 1.3
Gas LifeTime Concentration
(ppm)
Natural
Greenhouse Effect
(W/m2)
2. Greenhouse Gases (GHG)
2.2 Main Greenhouse gases (Pre-Industrial)
Contribution to Natural Greenhouse Effect
2. Greenhouse Gases (GHG)
2.2 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
…..
2. Greenhouse Gases (GHG)
2.2 Main Greenhouse gases (from pre-industrial to today)
- Increase from 1750
CO2 : +31 %
CH4 : +151 %
N2O : +17 %
O3 trop. : +36 %
IPCC, 2007
2. Greenhouse Gases (GHG)
2.3 Example : N2O cycle
• Fourth GHG in terms
of contribution
to anthropogenic
grenhouse effect
2. Greenhouse Gases (GHG)
2.3 Example : N2O cycle
Natural Sources (~11 TgN/yr) :
Natural Soils
(3.3-9.0 TgN/yr) Ocean
(1.8-5.8 TgN/yr)
Anthropogenic Sources (~ 6.7 TgC/yr) :
FF combustion
Agriculture
Biomass burning
Rivers, Estuaries…
Sinks (~12.5 TgN/yr) :
Stratospheric
Photolysis
2. Greenhouse Gases (GHG)
2.3 Example : N2O cycle
Ocean Source
RITS89 (Nevison, 2003)
Production N2O = f(denitrification, nitrification)
2. Greenhouse Gases (GHG)
2.3 Example : N2O cycle
Ocean Source
N2O Flux mgN/m2/yr
Data compilation: Nevison et al. 2005 :
Evolution of these
natural fluxes
with global warming?
- The total temperature increase from the period 1850 to 1899
to the period 2001 to 2005 is 0.76°C ± 0.19°C.
- Confirmed by others instruments (balloons, satellites..)
3.1 Recent observations (from IPCC 2007)
But Warming is not uniform
in time and space…
Warming trend over 1901-2005
Warming trend over 1979-2005
- Mid to high latitudes from N.H. : increase (+0,5/1%/decade) - sub-tropics (10N-30N) : decrease (-0.3%/decade)
Precipitations
“Most of the observed increase in
global average temperatures since
the mid-20th century is very likely
due to the observed increase in
anthropogenic greenhouse gas
concentrations.
“Most of the observed increase in global average temperatures
since the mid-20th century is very likely due to the observed
increase in anthropogenic greenhouse gas concentrations.
- from climate models
-Detection
/ Attribution techniques
2. What would you bet if you were asked
when will be the next glaciation?
Two questions to conclude…..
1. Why was Arrenhius right more one century
before the big IPCC-type models?
2. What would you bet if you were asked
when will be the next glaciation?
Two questions to conclude…..
1. Why was Arrenhius right more one century
before the big IPCC-type models?
>>> because he made 2 compensating mistakes
2. What would you bet if you were asked
when will be the next glaciation?
Two questions to conclude…..
1. Why was Arrenhius right more than one century
before the big IPCC-type models?
>>> because he made 2 compensating mistakes
>>> just come to the carbon cycle
modeling practical….
Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide
have increased markedly as a result of human activities since 1750 and now far
exceed pre-industrial values determined from ice cores spanning many thousands of
years.
The global increases in carbon dioxide concentration are due primarily to fossil fuel
use and land use change, while those of methane and nitrous oxide are primarily due
to agriculture.
Most of the observed increase in global average temperatures since the mid-20th
century is very likely due to the observed increase in anthropogenic greenhouse
gas concentrations.
Discernible human influences now extend to other aspects of climate, including
ocean warming, continental-average temperatures, temperature extremes and
wind patterns.
Warming of the climate system is unequivocal, as is now evident from observations
of increases in global
average air and ocean temperatures, widespread melting of snow and ice, and
rising global average sea level.”
GREENHOUSE GASES CONCENTRATIONS
WARMING AND OTHER ASPECTS OF CLIMATE
CAUSE-EFFECT RELATIONSHIP