Greenhouse Gases & Climate Change - SOLAS...

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Greenhouse Gases & Climate ChangeLaurent BoppLSCE, Paris

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

1958 Keeling begins direct measurement of CO2 in atmosphere

Introduction

2007 Last IPCC report :

Introduction

“Global atmospheric concentrations ofcarbon dioxide, methane and nitrousoxide have increased markedly as a result of human activities since 1750 andnow far exceed pre-industrial values determined from ice cores spanningmany thousands of years

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 atmosphericconcentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result ofhuman activities since 1750 andnow far exceed pre-industrialvalues determined from ice coresspanning many thousands ofyears

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”

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 ofthe 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 GreenHouseEffect

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),( /

TkchB ehcTF λ

λπλ (monochromatic emissive power of a black body)

Wien’s Law : Wavelength of maximum intensity with TTT /2897)(max =λ

Stefan-Boltzmann’s Law : hot bodies radiate more energythan cold ones

4TFB σ=

1. Earth’s radiative budgetNo spectral overlap between predicted spectra with temperatures similar to sun and earth

ObservationsPeak at 0.5 μm

Peak at 15 μm

Version 1 : Without any atmosphere

FeαS0S0

(1-α) S0 = σ Te4

S0 = 342 W m-2

Albedo α = 0.3Stephan-Boltzman Constant σ = 5.67 10-8 W m-2 K-4

Te = 255 K ! It is too cold…

1.2 Absorption of radiation by gases

The mechanism of absorption differs depending on the the wavelength

UltraVioletMolecule Dissociation

InfraRedMolecule Vibration

MicroWaveMolecule Turning

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 differentforms 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) and15.0 micron (C and D mode)

4.2 μm15 μm

Some greenhouse gases transmission spectra

Absorbing Spectrum :

- almost complete in UV- very low in the visible and near IR- IR : mainly H2O except in the 7-15

micron band

EmissionTemperature Surface

Temperature

Radiation emitted to space

Emitted Radiation from the surface

Absorption -emission by

Temperature

1.3 Greenhouse Principle

Surface : (1-α) S0 + Fa = Fe

Top of the Atmosphere : Fe - Fa = τFe + Fa

τFeαS0S0

Transparent atmosphere in SW Partially absorbing in IR

Version 2 : With an atmosphere (only one layer here…)

1.4 The Earth’s annual and global mean energy balance.

IPCC, 2001

2. Greenhouse Gases (GHG)

Atmospheric concentrations vary by more than eight orders ofmagnitudeRadiative efficiencies vary by more than four orders ofmagnitude,

enormous diversity in their properties and origins.

Greenhouse GasMean Concentration / BurdenRepartitionRadiative 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, …)

2.1 Useful definitions

Life time : Atmospheric burden divided by mean global sink for a gas in steadystate. Characterizes time to turn over atmospheric burden once.

CH4 : Atm. Burden : 1,774 ± 1.8 ppbSinks (mostly tropospheric oxydation with OH) 581 Tg(CH4)

12 years

N2O : Atm. Burden : 319 ± 0.12 ppbSink (mostly photolysis in the strat.): 12.5 TgN

114 years

CO2 : 5 yrs ? … 200 yrs ?… to be discussed tomorrow…

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 relatedto radiative forcing by ΔTs = λ RF

GWP (Global Warming Potential) : ratio of the time-integrated forcing from theinstantaneous 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 theconsidered 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)

NaturalGreenhouse Effect(W/m2)

2.2 Main Greenhouse gases (Pre-Industrial)

Contribution to Natural Greenhouse Effect

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 GasesCFCs, halons

- Tropospheric O3- Non-direct GHGs

- CO- NOx…..

Global Warming Potential

2.2 Main Greenhouse gases (from pre-industrial to today)

- Increase from 1750CO2 : +31 %CH4 : +151 %N2O : +17 %O3 trop. : +36 %

IPCC, 2007

- Hydrofluorocarbons - Chlorofluorocarbons

Evolution of major halogen-containing LLGHGs.

Contribution to Anthropogenic Greenhouse effect

IPCC, 2007

2.3 Example : N2O cycle

• Fourth GHG in termsof contributionto anthropogenicgrenhouse effect

Natural Sources (~11 TgN/yr) :

Natural Soils(3.3-9.0 TgN/yr)

Anthropogenic Sources (~ 6.7 TgC/yr) :

Ocean(1.8-5.8 TgN/yr)

FF combustionAgricultureBiomass burningRivers, Estuaries…

Sinks (~12.5 TgN/yr) :StratosphericPhotolysis

Ocean Source

RITS89 (Nevison, 2003)

Production N2O = f(denitrification, nitrification)

Ocean Source

N2O Flux mgN/m2/yr

Data compilation: Nevison et al. 2005 :

Evolution of thesenatural fluxes with global warming?

2. Greenhouse Gases

2.4 Projections underdifferentscenarios

IPCC 2001

3. Response of Climate

3.1 Observations3.2 A Cause-Effect relationship ?3.3 Projections

- 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…

Recent Warming compared to past 1000 y reconstruction

IPCC, 2007

- Mid to high latitudes from N.H. : increase (+0,5/1%/decade)- sub-tropics (10N-30N) : decrease (-0.3%/decade)

Precipitations

World Mountain Glaciers

Le glacier d’Argentière

(Alpes)

Snow cover and Sea-ice extent

Ocean : Heat Content

Ocean : Salinity

+ Oxygen , pH, …

Sea Level evolution

- from tide gauges / satellite

- mechanisms :

∂U∂t

+ 2Ω × U = .

Climate Models

“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

3.3 Projections

Temperature Change (°C)

IPCC, 2007

And a new glaciation… very unlikely in the next 100 yrs…

(If you come at the modelling practical, you’ll compute when will be next glaciation…)

Global atmospheric concentrations of carbon dioxide, methane and nitrous oxidehave increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands ofyears.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 globalaverage air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.”

WARMING AND OTHER ASPECTS OF CLIMATE

CAUSE-EFFECT RELATIONSHIP

GREENHOUSE GASES CONCENTRATIONS

Greenhouse Gases & Climate Change - SOLAS...

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