Ozone

1
(Flux in GtC/yr)
1 GtC (gigaton carbon) 109 metric tons
1012 kg 1015 grams (1 petagram Pg) 1 Tg
(teragram) 1012 grams
Fast exchange (75 m.)
Permanent sink
(GtC)
2
Anthropogenic sources -fossil fuels cement 6.3
GtC/yr -permanent deforestation 1.6
GtC/yr
CO2 fixation
Fast exchange
Permanent sink
3
Anthropogenic sources -fossil fuels cement 6.3
GtC/yr -permanent deforestation 1.6
GtC/yr Fate of anthropogenic CO2 42 stays in
air longer than 1 yr 29 absorbed by ocean
surface 29 Northern Hemisphere land
CO2 fixation
Fast exchange
Permanent sink
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• Residence time (yr) steady-state concentration
  (ppm)/ input rate (ppm/yr)
• Can also be defined with respect to output rate
• Can be well-defined if there is a known removal
  mechanism
• (example CH4 is removed by reaction with
  hydroxyl radical in the
• troposphere in a reaction with established
  kinetics)
• For CO2, the removal mechanisms are complex
• (i) photosynthesis cycle terrestrial biosphere
  absorption (fast)
• (ii) dissolution in oceans (hundreds of years)
• (iii) reactions in ocean to equilibrate with
  CaCO3 (thousands of yrs)
• (iv) weathering reactions (hundreds of thousands
  of years)
• After 1000 years 15-30 of CO2 remains in the
  atmosphere
• After 100,000 years 7 of CO2 remains in the
  atmosphere

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Long-term fate of atmospheric CO2 following a
large release from fossil fuel burning
today
Climatic Change 90, 283-297 (2008)
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At T 288K, Iout 390 W/m2
LOSU assessed level of scientific understanding

• Radiative forcing imbalance in the energy
  equilibrium of Earth
• change in solar insolation rate
• change in IR absorption/reradiation (natural or
  anthropogenic)
• Requires then a reequilibration (fast in
  stratosphere generally slow in troposphere)

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Human and natural influences affect the drivers
for climate change, which then in turn affect
RF and have lag effects (such as changes in
evaporation). This leads to a large-scale
climate change and response, later modified by
human mitigation or a biogeochemical feedback
in Nature.
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FEEDBACK process whereby the result affects
its origin (cause-effect loop) -can be positive
(amplifies original phenomenon) or
negative (dampens original phenomenon)
ICE ALBEDO FEEDBACK original cause
anthropogenic fossil fuel burning affected
climate change driver CO2 trapping of IR
light radiative forcing is the primary effect
climate response increased temperature
feedback positive increased melting of
ice decreases overall Earth albedo, leading to
more overall absorption of Isolar, producing
higher temperatures, leading to more ice
melting lag effect positive, increased
evaporation of H2O leading to further IR
trapping. ? Implicates another positive
feedback water vapor positive feedback.
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FEEDBACK process whereby the result affects
its origin (cause-effect loop) -can be positive
(amplifies original phenomenon) or
negative (dampens original phenomenon)
EXAMPLES OF NEGATIVE FEEDBACKS hydrological
cycle prevents runaway of water vapor positive
feedback radiative damping increased T leads
to increased Iout Iout seT4
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At T 288K, Iout 390 W/m2
LOSU assessed level of scientific understanding

• Radiative forcing imbalance in the energy
  equilibrium of Earth
• change in solar insolation rate
• change in IR absorption/reradiation (natural or
  anthropogenic)
• Requires then a reequilibration (fast in
  stratosphere generally slow in troposphere)

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Methane levels - 7.66 mm absorption band -
about 2.5-fold increase since 1800 - leveling
off since 1999 is not well understood, but
may be decreased inputs to balance sinks
(Bousquet et al., Nature 443, 439 (2006)
Wuebbles Hayhoe, Earth-Sci Rev. 57,
177-210 (2002))

• Chief atmospheric sink for methane
• CH4 ?OH ? ?CH3 H2O
• (residence time 12 years)
• Effectiveness over 100 years 23x
• higher than CO2 (per-molecule basis)
• Note also the water generation (stratosphere)

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Nature 443, 71-75 (2006) also Science 318, 633
(2007)

• Warming-induced permafrost melting and lake
  expansion
• Increased rates of methane bubbling
• Methane exists as a caged frozen hydrate with ice
  (methane hydrate)
• Methane hydrates may be the worlds largest
  fossil fuel resource!!

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Possible methane hydrate release from shallow
ocean sediments
This scenario is very unlikely in the next
century But thawing of the Arctic permafrost and
large-scale CH4 release is possible without
coupling to sea level rise
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Sources of methane anthropogenic and natural
marsh gas
Natural sources
Anthropogenic sources
Approximate overall estimates Natural 140-235
Tg CH4/yr Agriculture 141 Tg CH4/yr Anthro,
non-Ag 217 Tg CH4/yr What is the ultimate
origin of CH4?
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ANAEROBIC CARBON AND HYDROGEN CYCLES
Clostridia
anaerobic environment

• Reduced CH2O from photosynthesis undergoes
  fermentation (disproportionation)
• reactions to generate a variety of
  small-molecule products
• Methanogenesis exploits this process 4H2 CO2 ?
  CH4 2H2O
• Methanogens are chemoautotrophs and depend on H2
  generated by other
• microorganisms, such as Clostridia, or on
  geologic H2.
• Redox half-reactions
• 4 H2 ? 8 H 8 e- E 400 mV
• CO2 8 H 8 e- ? CH4 2 H2O E -250 mV

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• Methanococcus jannaschii
• Strict anaerobe
• Optimal growth temperature 85C
• Autotrophic, nitrogen fixer
• 4H2 CO2 ? CH4 2H2O
• Exclusively hydrogenotrophic
• Central role in global carbon cycling

Methanogens account for 70 of the total
global methane source
black smoker chimney East Pacific Rise
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Methanogenesis
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Microbial biogeochemistry coupled reactions in
distinct microorganisms
Methane monooxygenase enzyme (MMO)
catalyzes CH3OH production from CH4. Overall
pathway CH4 O2 ? CO2 H2O
Methanococcus, Methanosarcina, etc
Clostridia
Anaerobic reactions in the lake sediment are
dependent on the detritus from photosynthesis,
which is drifting downward
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At T 288K, Iout 390 W/m2
LOSU assessed level of scientific understanding

• Radiative forcing imbalance in the energy
  equilibrium of Earth
• change in solar insolation rate
• change in IR absorption/reradiation (natural or
  anthropogenic)
• Requires then a reequilibration (fast in
  stratosphere generally slow in troposphere)

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Nitrous oxide, N2O Bond stretch at 7.8 mm Angle
bend at 8.6 mm
Preindustrial concentration 270 ppb Atmospheric
half-life 114 years Effectiveness compared to
CO2 296x

• Anthropogenic driver microbial (increased
  fertilizer use)
• Implicates the global nitrogen cycle in climate
  change

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Global warming potentials for CFCs and related
compounds
CFCs

• per-molecule effects can be several
• thousand fold greater than CO2.
• residence times are 1-1700 yrs.
• SF6 residence time 3200
• efficiency 37000x CO2. Used as an
• insulating gas in semiconductor
• industry. Now recycled, not vented.

data from IPCC4
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Effects of ozone (O3).
Stratospheric ozone anthropogenic effect is
toward cooling due to depletion by CFCs and
similar compounds. Tropospheric ozone arises
from photochemical smog as a secondary
ground-level pollutant, from NO and volatile
organics under the influence of sunlight.
Significant warming effect. Controllable with
smog reduction technology.
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Albedo influence on heat balance

• Varies greatly over the Earths surface (average
  30)
• -as low as 6 in the oceans (most energy
  absorbed)
• -agricultural and forest land are low albedo
  (10-20)
• -deserts are higher (25-40)
• -global average for clouds (35-40)
• -snow and ice cover (40-80)

Cropland/pasture in 1750 6-7 of global land
surface Cropland/pasture in 1990 35-39 of
global land surface Decrease in forest cover by
8 of global land surface Estimated total effect
small net cooling (increased albedo) Black
carbon on snow increases melting, small net
warming (decreased albedo)
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Solar irradiance changes (natural forcing)
data from IPCC4
Possibly a small influence toward warming poorly
understood
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At T 288K, Iout 390 W/m2
LOSU assessed level of scientific understanding

• Radiative forcing imbalance in the energy
  equilibrium of Earth
• change in solar insolation rate
• change in IR absorption/reradiation (natural or
  anthropogenic)
• Requires then a reequilibration (fast in
  stratosphere generally slow in troposphere)

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Effects of particles and clouds on albedo
Cloud types

• Clouds dominate albedo reflect incoming
  sunlight, but reradiate
• the IR radiation coming from the Earths surface
• Clouds form from water condensation, but depend
  also on particles
• Biggest unknown in climate modeling is the effect
  of clouds, which in
• turn depend significantly on presence of aerosols

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Effects of particles and clouds on albedo
Cloud types

• Cirrus very thin ? little reflection of Isolar.
  But absorbs Iup (IR) from
• warmer ground and reradiates colder light ? net
  warming.
• Reradiation to space is from cloud top, so that
  T is relevant.

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Jet airplane contrails Climate effects similar
to cirrus clouds cause surface warming. How?
Jet emissions particles nucleate condensation
of atmospheric water Dissipation within a few
days 9/11 effect
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Effects of particles and clouds on albedo
Cloud types
focused convection
broad, diffuse convection

• Cirrus very thin ? little reflection of Isolar.
  But absorbs Iup (IR) from
• warmer ground and reradiates colder light ? net
  warming.
• Reradiation to space is from cloud top, so that
  T is relevant.
• Cumulus and stratus hold much more water.
• 2/3 of Earth albedo derives from these clouds,
  so very small
• changes in extent have large effects. Little IR
  effect.

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General effects of aerosols to promote cooling
Particles in the atmosphere absorb light
depending on their albedo Size of particle is
important larger particles absorb more light,
and smaller particles tend to scatter (reflect)
light. Most are submicron ? scattering
(cooling) dominates Black soot absorbs much
light ? local warming in the atmosphere Sulfate
-rich aerosols reflect light because of high
albedo ? cooling effect on the air near ground
level. Both natural and anthropogenic SO2
emissions oxidize to H2SO4 in small aerosol
droplets. Overall, anthropogenic pollution
increases particles in the atmosphere by an
estimated 25-50 global dimming Natural
condensation nuclei sea salt, dust, pollen,
smoke, biogenic sulfur
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Mount Pinatubo eruption, Philippines, 15 June
1991 ejected 10 Tg SO2 (1 Tg 1012 g) slowed
the rise of global warming Approximate albedo
increase of 0.5 ? T decrease of 0.5 K
SO2 (g) ? ? H2SO4 (aq) ? acid rain
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H2S
DMS
FeS2
1012 gram 1 teragram (Tg)
Sulfur emissions occur from both anthropogenic
and natural sources
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Anthropogenic generation of SO2

• Anthropogenic sources from coal (mainly) and oil
  combustion
• H2S is also an anthropogenic source (from oil and
  CH4 processing
• natural gas reservoirs often contain
  significant H2S)
• Sulfide ores are also a source of SO2 when
  processed to yield the
• elemental metal, for example
• 2NiS(s) 3O2(g) ? 2NiO(s) 2 SO2(g)
• The SO2 can be oxidized to SO3, then converted to
  commercial H2SO4
• SO2 in power plant emissions is scrubbed by
  reaction with CaCO3
• to yield CaSO4 (CO2)
• Paradox reduced sulfur emissions alleviate
  particulate pollution,
• acid rain, but also exacerbate global warming.

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incorporation of S into protein, etc.
1.
(6)
2.
6
-2
3.
(-2)
4.

• Energy-requiring conversion from SO42- to H2S
  occurs in the
• sulfate-reducing bacteria (steps 1 - 4).
• Very common in anaerobic marine sediments
• SO42- 2CH2O 2H ? H2S 2H2O 2CO2
• The energy is provided by oxidation of reduced
  carbohydrate
• Sulfate-reducing bacteria (SRB) often live in
  consortium with methane-
• oxidizing bacteria (methylotrophs)
• If oxygen is available, methylotrophs carry out
  CH4 2 O2 ? CO2 2 H2O
• In a consortium of SRB with methylotrophs,
  anaerobic oxidation of CH4
• is coupled to reduction of SO42-. Example of
  syntrophy.

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Anaerobic oxidation of methane Syntrophic
interaction between SRB and methylotrophs
Nature 407, 623-626 (2000). Scale bar 5m.
Fluorescent probes to species-specific 16S rRNAs

• Sulfate-reducing bacteria
• SO42- 2CH2O 2H ? H2S 2H2O 2CO2
• If oxygen is available, methylotrophs carry out
  CH4 2 O2 ? CO2 2 H2O
• But in a consortium of SRB with methylotrophs,
  anaerobic oxidation of CH4
• is coupled to reduction of SO42-. Occurs in
  marine sediments.
• Example of syntrophy. Blocks escape of CH4
  to the atmosphere.
• Proposed overall reaction CH4 SO42- ? HCO3-
  HS- H2O
• Issues what intermediates are transferred? How
  to maintain favorable energetics?

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• Sulfide oxidation mediated by bacteria can occur
  from iron sulfide ores
• H2S oxidation produces an acidic environment
  acidothiobacillus also
• oxidizes Fe2 to Fe3. Oxidation can be via
  O2 or other oxidizers.

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Volatile Organic Sulfur
bacterial
bacterial
H2S is rapidly oxidized photochemically in the
atmosphere ? inorganic S does not have a
significant global effect But dimethyl sulfide
(DMS) does enter the atmosphere ? photochem
conversion to CH3SO3- (methane sulfonic acid)
? cloud condensation nuclei
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Link between methane production rates and
industrial sulfur emissions?
Schimel J, PNAS 101, 12400 (2004)
industrial emissions
microbial ecology
Competition between methanogens and sulfate
reducing archaebacteria, for nutrients in
anaerobic environments, is affected by sulfur
emissions. In turn, levels of atmospheric
methane are affected.
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