Greenhouse Gases & Climate Change - SOLAS · PDF file1.2 Absorption of radiation by gases -...

Greenhouse Gases & Climate Change

Laurent Bopp

LSCE, 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

Adapted from Lüthi et al. 2008, Loulergue et al. 2008, and Schilt et al. 2010

1958 Keeling begins direct measurement of CO2 in atmosphere

Introduction

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


“

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”


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


No spectral overlap between predicted spectra with temperatures similar to sun and earth

Observations Peak at 0.5 mm

Peak at 15 mm


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…


1.2 Absorption of radiation by gases

The mechanism of absorption differs depending on the the wavelength

UltraViolet

Molecule Dissociation

InfraRed

Molecule Vibration

MicroWave

Molecule Turning


1.2 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


1.3 Greenhouse Principle


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…)


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 of

magnitude

Radiative efficiencies vary by more than four orders of

magnitude,

enormous diversity in their properties and origins.


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, …)


2.1 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…





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









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)


2.2 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 Gases

CFCs, halons

- Tropospheric O3

- Non-direct GHGs

- CO

- NOx

…..

Global Warming Potential

Global Warming Potential


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

- Increase from 1750

CO2 : +31 %

CH4 : +151 %

N2O : +17 %

O3 trop. : +36 %

IPCC, 2007

- Hydrofluorocarbons - Chlorofluorocarbons

Evolution of major halogen-containing GHGs.

Contribution to Anthropogenic Greenhouse effect

IPCC, 2007 (Present time vs. 1750)


2.3 Example : N2O cycle

• Fourth GHG in terms

of contribution

to anthropogenic

grenhouse effect



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



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 these

natural fluxes

with global warming?

2. Greenhouse Gases

2.4 Projections

under

different

scenarios

IPCC 2001

3. Response of Climate

3.1 Observations

3.2 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)

(GISS, 2011)

2010

1998 2005

(GISS, 2011)

But Warming is not uniform

in time and space…

Warming trend over 1901-2005

Warming trend over 1979-2005

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)

1850

1960

Snow cover and Sea-ice extent

(NSIDC, 2011)

(NSIDC, 2011)

Ocean : Heat Content

Ocean : Salinity

+ Oxygen , pH, …

Sea Level evolution

- from tide gauges / satellite

- mechanisms :

3.2 A cause-effect relationship ?

Historical Radiative Forcing

U

t 2 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)

New scenarios (RCPs) for the next IPCC AR5 (2013).

RCP : Representative concentration pathways

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?




1. Why was Arrenhius right more one century


>>> because he made 2 compensating mistakes




1. Why was Arrenhius right more than one century


>>> 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

Date post:	02-Mar-2018
Category:	Documents
Upload:	trinhdan
View:	220 times
Download:	5 times

Greenhouse Gases & Climate Change - SOLAS · PDF file1.2 Absorption of radiation by gases -...

Documents