Atmospheric composition and the greenhouse

Atmospheric Composition
and the Greenhouse
12.340 Global Warming Science
February 23, 2012
Dan Cziczo
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A Little About Myself…

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Today’s Class
• Why are atmospheres important?
-Bare rocks and blankets (the greenhouse concept)
•What are the Earth’s greenhouse gases? Where are they
from?
•Paleo versus modern greenhouse levels

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Recap
All others

Argon

Early Atmosphere
Probably H2, He
- Likely lost to space early

Carbon dioxide

Later Atmosphere
- Volcanic out gassing + impacts
: H2O, CO2, SO2, CO, S2, Cl2, N2, H2,
NH3, and CH4

Oxygen

Nitrogen

O2 ?
Ocean Formation ?

Image by MIT OpenCourseWare.

4

Lutgens and Tarbuck, The
Atmosphere, 8th edition


Planetary Temperature
Let’s start by
assuming the Earth
is a rock heated by
the sun with no
greenhouse gases

Earth

Sun Light

Earth Light
Image by MIT OpenCourseWare.

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Unless otherwise specified: Archer, Global Warming


‘Bare Rock’
Energy in = energy out
Fin = Fout (Watts)
From Archer: Intensity = W/m2
Fin[W] = I[W m-2] x (1-a) x Area[m2]

What is I? What is albedo?

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This image has been removed due to copyright restrictions. Please see the
image on page />
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Fin
Area = pr2 (why not

4pr2?)
Earth

Fin =Iin x (1-a) x Area
Fin = Iin x (1-a) x pr2

Sunlight
Image by MIT OpenCourseWare.

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Fig 3-1


Fout
Stephan-Boltzmann
Equation

Fout=Iout x Area
Iout = esT4

Earth

Area = 4pr2 (why not
pr2?)

e = ‘emissivity’, 0Earth Light
Image by MIT OpenCourseWare.

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‘Bare Rock’

Earth

Sun Light

Earth Light
Image by MIT OpenCourseWare.

4prearth2esTearth4 = prearth2(1-a)Iin
Tearth= [(1-a)Iin/4es]1/4
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Sun Light

Earth Light

4

(1 - α)lsolar

εσT

earth

4

Earth
What's Wrong?
l

α (%)
3

T
(K)
5

-2
(Wm
0 )

Venus

71

240

2600

Earth

33

251

1350

Mars

17

216

600

Planet

1

solar

Image by MIT OpenCourseWare.
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Let’s Add an Atmosphere
Sun Light

Earth Light

Fout = 4prearth2esTearth4
Define Iout = esTearth4 [W m-2]
4

εσT

(1 - α)lsolar

earth

4

Fin = prearth2(1-a)Iin
Define Iin = (1-a)Iin/4

Earth

Image by MIT OpenCourseWare.

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1 Layer
Boundary to space

(1 - α)lsolar

lup, atmosphere

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The Balance:
Iin,solar = = (1-a)Iin/4
Iup,ground = esTgrnd4

ldown, atmosphere
lup, ground

Iup,atmosphere = esTatm4
What is Tgrnd?

Earth

Image by MIT OpenCourseWare.
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1 Layer
Boundary to space

(1 - α)lsolar

lup, atmosphere

The atmosphere is
like the bare rock:

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Iup,atm = Iin,solar
esTatm4 = (1-a)Isolar/4
ldown, atmosphere
lup, ground

Earth

Image by MIT OpenCourseWare.
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Tatm= [(1-a)Iin/4es]1/4


1 Layer
And the ground is
now warmer:

Boundary to space

(1 - α)lsolar

lup, atmosphere

4

Iup,atm + Idown,atm = Iup,grnd
2esTatm4 = esTgrd4
ldown, atmosphere
lup, ground

Tgrd = [2]1/4 Tatm (~1.2Tatm)
Tgrd= [(1-a)Isolar/2es]1/4

Earth

Image by MIT OpenCourseWare.

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Boundary to space
(1 - α)lsolar

lup, atmosphere

4

ldown, atmosphere
lup, ground

Earth
What about Venus and Mars?
Planet

α (%)

T

T

observed

T

1 layer

l

solar

(K)
5

(K)

(K)

(Wm-2)

Venus

71

240

700

285

2600

Earth

33

251

295

303

1350

Mars

17

216

240

259

600

Image by MIT OpenCourseWare.
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If It Wasn’t For Greenhouse
Gases We Wouldn’t Be Here!
(or we’d look a lot different)
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This image has been removed due to copyright restrictions.
The image is from Ruddiman, W. F., 2001. Earth's Climate: past and future.

W.H. Freeman & Sons, New York.

“Runaway Greenhouse”

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“The Goldilocks Effect”


Earth’s Atmosphere
The Earth’s
atmosphere can be
mimicked by a 1
layer atmosphere
but is much more
complex

Figure by MIT OpenCourseWare.
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Greenhouse Gases
All others

Argon

Table: Principal gases of dry air

Carbon dioxide

Constituent

Oxygen

Nitrogen

Image by MIT OpenCourseWare.

Percent by
volume

Concentration in Parts
Per Million(PPM)

Argon (Ar)

0.934

9,340.0

Carbon dioxide (CO2)

0.036

360.0

Helium(He)

0.000524

5.24

Hydrogen (H2)

0.00005

0.5

Krypton (Kr)

0.000114

1.14

Methane (CH4)

0.00015

1.5

Neon (Ne)

0.00182

18.2

Nitrogen (N2)

78.084

780,840.0

Oxygen (O 2)

20.946

209,460.0

Image by MIT OpenCourseWare.

figure and table fron Lutgens and Tarbuck, The Atmosphere, 8th edition)

Carbon dioxide, methane and nitrous oxide are natural (as well as anthropogenic)
More on CO2 in a moment.
Methane (CH4) – from wetlands, grazing animals, termites, and other sources
Nitrous Oxide (N2O) – from denitrifying bacteria
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Where Do Greenhouse Gases
Come From (and go)?
CO2

CO2

0.2 Gton / yr

H2O + CO2 -> H2CO3 (soil)
Volcano

Hot Spring

H2CO3 + CaSiO3 -> CaCO3 + SiO2 +H2O

Melting

Image by MIT OpenCourseWare.

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Ruddiman,2001


Greenhouse Gases
Vegetation: 610

Soils:
1560

Atmosphere: 600
(Pre-industrial)
Ocean mixed layer: 1000

What if volcanoes stopped?
Concept of lifetime:

Deep ocean: 38,000
Sediments and rocks:
66,000,000

Abundance (Gton) /Emission
(Gton/yr)= Lifetime (yr)

A Major carbon reservoirs (gigatons; 1 gigaton = 1015 grams)
Image by MIT OpenCourseWare.

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Ruddiman,2001


Greenhouse Gases Record

Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report
of the Intergovernmental Panel on Climate Change, Figure 6.1. Cambridge University Press. Used with permission.

This image has been removed due to copyright restrictions.
Please see the image on page
/>23


Paleo Changes in GGs

Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report
of the Intergovernmental Panel on Climate Change, Figure 6.4. Cambridge University Press. Used with permission.
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IPCC

Greenhouse Gases
All others

Argon

Table: Principal gases of dry air

Carbon dioxide

Constituent

Oxygen

Nitrogen

Image by MIT OpenCourseWare.

Percent by
volume

Concentration in Parts
Per Million(PPM)

Argon (Ar)

0.934

9,340.0

Carbon dioxide (CO2)

0.036

360.0

Helium(He)

0.000524

5.24

Hydrogen (H2)

0.00005

0.5

Krypton (Kr)

0.000114

1.14

Methane (CH4)

0.00015

1.5

Neon (Ne)

0.00182

18.2

Nitrogen (N2)

78.084

780,840.0

Oxygen (O2)

20.946

209,460.0

Image by MIT OpenCourseWare.

figure and table fron Lutgens and Tarbuck, The Atmosphere, 8th edition)

Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report
of the Intergovernmental Panel on Climate Change, Table 2.1. Cambridge University Press. Used with permission.
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