Greenhouse Effect and Atmospheric Chemistry

In nature there are neither rewards nor punishments –there are consequences
Robert tG G. Ingersoll
The Greenhouse Effect
‐ the atmospheric energy balance ‐

Organic Carbon Cycle
The pre‐industrial (1800) amount of CO 2 in the
atmosphere was 600Gt, balanced by equilibrium
between absorption by photosynthesis and
sequestration and emission through respiration
and release.
d(
CO2)
dt
d(
CO2)
dt
d(
CO2)
dt
abs
abs
ems
d(
CO2)
dt
Gt
74
y
atm
atm
ems
0
ocean
Gt
74.6
y
ocean
0.6
Gt
y
Gt
50
y
soil
soil
100
Gt
y
Gt
50
y
photosynth.
respiration
Each process has its own time scale depending
on the conversion rate which in turn depend on
environmental conditions such as light, water,
temperature. The conversion rate is proportional
to the product of CO 2 abundance in the reservoir,
the conversion cross section and the
leaf area A.
R
conv
N ,
CO
2
L,
H T A

Photosynthesis
chlorophyll
sunlight
C
6
H
O 6
O
6
CO2
6
H
2
O
12 6
6
2
and respiration
C 6 H12 O6
6
O2
6
CO2
6
H
2
O
Chemical reaction takes place
on a pico‐second timescale
which translates into a high
reaction probability or crosssection.
The absorption yield
depends on the cross section
integrated over the spectrum of
the incoming light and the
luminosity the actual light
absorption and conversion
cross section depends on the
wavelength, the leaf structure,
t
the pigment composition and
the cell conversion mechanism.
The timescale for CO 2 absorption is fast, making
photosynthesis an extremely efficient absorption
process if sufficient leaf surface area is available!

Change of balance
Increase of CO 2 emission and increase of deforestation since the 19 th century!

Drastic increase of the anthropogenic
CO 2 production due to fossil fuel
consumption by growing
industrialization
Impact on CO 2 equilibrium conditions, which
maintain the present status quo in climate !

Observational evidence, CO 2
YEAR
The dashed red line with diamond symbols represents the monthly mean values,
centeredonthemiddleofeachmonth.Theblack line with the square symbols
represents the same, after correction for the average seasonal cycle. The curve shows
a continuous increase of the CO 2 level in Earth’s atmosphere .

CO 2 Global Distribution
2

Strong seasonal variations
due to climate variances
between the northern and
the southern hemisphere
and feed back correlations
over the year.
CO 2 observations from Mauna
Loa reflect medium location in
northern hemisphere, but the
observations reflect consistently
the seasonal variations in CO 2 emission

Other Greenhouse Gases
N 2 O nitrous oxide level was stable
for the last 3000 years according to
ice core analysis. The present
annual increase in emission i by 0.2%
to 0.3% is due to widespread and
rapidly increasing applications of
nitrogen based fertilizers, tropical
deforestation, and conversion of
forest to pasture and farmland.
CH 4 methane increases at an annual rate of 0.8% to
1%. Thistrackswell with ihpopulation growth. Naturally
occurring from wetlands such as bog and swamp
emissions the increase is associated with rice
cultivation, landfills, biomass burning, mining, natural
gas venting, and pipeline leaks. Release of CH 4 from
Alaskan and Siberian permafrost regions could result
in an sudden increase by 500Gt within next century.
CFC chlorofluorocarbons have been
developed in the 1920ies for
cleaning solvents, refrigerants, and
propellants spray cans. Industrial
mass production after 1950 caused
an unprecedented increase. Inert to
chemical processes expected to
occur in the troposphere, p CFCs
accumulate in the stratosphere,
where photodissociation breaks up
molecules, releasing halogen gases.

Anthropogenic sources of CO 2

Alternative World Views
http://www.worldmapper.org/display.php?selected=295
Territory size shows the proportion of carbon dioxide emissions in 1980, 2000, 2006.
CO 2 emission 1980 CO 2 emission 2000
>17t/p
>2t/p
~8t/p
~6t/p
>2t/p
~3t/p
CO CO emission 2006 per capita
2 emission 2006 2
"... the world need[s] to differentiate between the survival emissions of
the poor and luxury emissions of [the] rich." Sunita Narain, 2002

Greenhouse gases
Greenhousegasestraptheemittedinfraredradiationfromearthsurfaceinthe
lower troposphere by atomic or molecular absorption processes, causing a
gradual heating of the lower atmosphere layer.
H 2 O is the most natural occurring greenhouse gas (humidity, clouds). CO 2 is
2 2
primarily an anthropogenic greenhouse gas (industry, traffic). Additional
anthropogenic greenhouse gases are industry produced Chlorofluorcarbons
(CFCs) and Hydrofluorcarbons (HCFCs).

Single layer Greenhouse model
Infrared radiation from theearth surface of emission i temperaturet
T e is completely absorbed in atmosphere and radiates into space
and back to earth surface increasing surface temperature T s .
F 0
( 1
)
F
Incoming net solar flux:
0
F avg
F 0 4
( 1 ) F
i
4 0
Emission temperature: T e
F
Flux A ↑ radiated to space
depends on atmospheric
temperature T a :
A
T
4
4
a
A
F
F ↑
Flux S ↑ radiated from
F
surface with terrestrial
T
A 0
F T
s
surface temperature T
in
s
4 F
Ts
2
4
s
( 1 )
0
4
4
Te
Te
4
T 2 T
1. 19 T
e
e
Emission temperature
T =255K=‐18 o e C
Surface temperature:
T s =303K=30 o C
4

Considering a change in albedo
and an atmospheric absorption
T e
T
s
4
4
1
F
4
0
1
F0
2 T
4
e
2
Earth’s surface temperature depends on
the albedo . Increasing the albedo
(reflection of incoming radiation) reduces
the emission temperature T e and therefore
also the temperature T s of the earth
surface. Enhanced cloud coverage would
cause a temperature reduction.
T
T
2
of the emitted radiation is absorbed by the
2
atmosphere (full absorption =1) reduces
s
4 T e
a
4
1 1
T
4
e
2
2
T
No absorption: 0 ≤ ≤ 1 full absorption
s
A leaky greenhouse where only a fraction
the greenhouse effect and lowers the
surface temperature T s (This corresponds to
a reduction of greenhouse gases) and also
the atmospheric temperature T a .

Examples
320
T
s
2
1 1
T T
T
2
2
2
4
e a
4 4
e
T
s
Tempe erature [K]
300
280
260
240
220
200
0 0.2 0.4 0.6 0.8 1 1.2
The globally averaged solar incident
(or emitted) flux F e on the surface is
only a fraction f≈0.16 (for =0.35)
of the incoming total flux F o .
Te
Ts
Ta
T e
4
1
F
4
Emission temperature depends
on the amount of incoming solar
radiation flux, the insolation F o !
4 1
Fe
Te
F
4
W 1 0.35 W
1 6
2
m 4 m
0
0
2

Climate feed‐backs
Greenhouse models have to account for several potential positive or
negative feedbacks that can occur, if the equilibrium of the climate system is
perturbed by an additional energy input or energy loss dQ (in units W/m 2 ).
The impact can be expressed in terms of surface temperature change dT s .
dTs
Ts
dQ QQ
is a measure for climate sensitivity
4
3
QBB Te
4 Te
Te
4
Te
since const
T
T
Q
s
BB
s
K
Wm
T
3
e
T
3
1
4
T
0.26
for
T
255
K
2
e
For every Q=1 Wm ‐2 increase in the forcing of energy balance at the earth’s
surface, the surface temperature T s will change by 0.25K ! Each such change
requires altering total insolation by 6 Wm ‐2 due to albedo or geometrical shifts!
s
e

Climate feedback from water vapor in the atmosphere depends on the
saturated vapor pressure SVP. If the temperature increases the amount
of water at saturation ti increases, enhancing the greenhouse effect of
water and raising the temperature (humid and hot weather conditions).
SVP
A
e
0.06706
T
A 6.11mbar
0
C
1
A change by 1 o C leads to a 7% change in SVP
Ts K
0.5
for Te
255K
2
Q
Wm
BBH
2
O
See lecture 7.1.
d SVP
SVP
dT s
Taking into account the water vapor for every Q=1 Wm ‐2 increase in the
forcingofenergybalancethesurfacetemperatureT s will change by 0.5K !
This is a positive feedback of water vapor formation. However, water
vapor will favor cloud formation which increases albedo, reduces
insolation and therefore reduces temperature as negative feedback.

Observed annual global temperature
trends compared with the simulated
global mean surface temperatures,
considering separately the natural and
anthropogenic forcing contributions.
The observed trend suggests an
increasing dominance of anthropogenic
based forcing contributions. This
conclusion is still heavily contested!

Temperature increase predictions as
a function of future CO 2 emission

Predictions IPCC 2001 for the development
of mean temperatures in Europe until 2080 Reality in summer 2010
Comparison with 2003
Science 332 (2011)

Conclusions by the intergovernmental Panel on Climate Change (IPCC)
Possible consequences
predicted by theoretical
model dl studies of the
IPCC and other research
institutions or research
groups.
Detailed analyses and
study are summarized
in a number of different
reports by the National
Academies and are
available on‐line:
www.nap.edu/topics.php?topic=367

Counterstrategies: how to cool the
earth by climate‐ or geoengineering
g g