The importance of longevity in a greenhouse gas as climate forcing

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The importance of longevity in a greenhouse gas
as climate forcing

• David Archer
• University of Chicago

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Joseph Fourier
Joseph Fourier described the greenhouse effect in
1827
Memoires d lAcademie Royale des Sciences de
lInstitute de France VIIII, 570-604 (1827)
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Energy Balance of a Bare Rock
Tearth 259 K -14 C 6F
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A Planet with an Atmosphere
Tatm 259 K
Tearth 303 K 86 F
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John Tyndall, 1859
John Tyndall discovered that CO2, H2O, and CH4
are greenhouse gases. O2 and N2 are not.
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CO2 is a greenhouse gas
Symmetric Stretch
Resting State
C
O
C
O
O
O
No Resting Dipole
IR
Inactive
Asymmetric Stretch
Bend
C
O
O
C
O
O
-1
-1
2349
cm
660
cm
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Earths outgoing infrared spectrum
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The band saturation effect
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Radiative Forcing goes as ln(CO2)
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Svante Arrhenius
Svante Arrhenius calculated that doubling CO2
would warm the Earth by 4-6C, in 1896
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The water vapor feedback

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The Runaway Greenhouse Effect
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The ice albedo feedback

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David Keeling
David Keeling started measuring CO2
concentration in the atmosphere
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The biosphere breathes
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Various public predictions of detectable
human-caused warming by year 2000
Charney report and others
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Climate forcings
Only greenhouse gasforcing looks like therecent
temperature rise.
Crowley, 2000
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What about phenomenaundreamed-of?
The sun is good at pushing our climate buttons.
Clouds? Humidity? They blame CO2 because
they cant think of anything else.
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A detective story
The Butler. Found holding a smoking gun next to
the deceased. Forensics matches the gun with the
bullets. The Chauffer. In Kentucky for
sisters wedding. Cant think of any way he
could have done it. To convict the Chauffer,
wed have to first unconvict the Butler.
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Airborne fraction of fossil fuel CO2
Century timescale peak
Airborne Fraction of Carbon Released
Millennial timescale tail
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IPCC 2001 and earlier Summaries for Policymakers
IPCC 2001 and earlier reports implied that
global warming would last about a century.
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Everyone gets this wrong
Rutledge 2011
Shindell, 2012
Ramanathan 2008
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Paleocene/Eocene Thermal Maximum Event 55 Myr Ago
A natural releaseof CO2, comparableto the
potential fossil fuel release. Warming, with a
recovery that took100,000 years.
Zachos et al. 2001
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Long Tail Model Intercomparison Project LTMIP
D. Archer, M.l Eby, V. Brovkin, A. Ridgwell, L.
Cao, U. Mikolajewicz, K. Caldeira, K. Matsumoto,
G. Munhoven, A. Montenegro, Ann. Rev. Earth
Sciences, 2009.
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Band saturation effect of IR absorbtion by CO2
emphasizes the tail
1800
1600
1400
1200
pCO2
1000
800
600
400
200
0
6
5
C
4
3
2
1
0
0
100
300
500
200
400
kyr
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Seawater pH Chemistry
CO2 CO3 H2O lt--gt 2 HCO3-
10
100
2000 mM
Concentration in seawater
CO2 uptake capacity is determined by CO3
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Atmosphere / Ocean Equilibrium
600 Gton C
1800 Gton C as CO3
We expect a partitioningof 13 between air
andocean
Gton C 1015 g
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Atmosphere / Ocean Equilibrium
Airborne Fraction of CO2 Slug
1000-2000Gton
4000-5000Gton
Archer 2005 22 33 Lenton 2006 21-26 34 C
LIMBER 22 35 Goodwin 2007 24-26 40 Ridg
well 2007 31
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Atmosphere / Ocean Equilibrium
Affected by changes in circulation biology o
cean temperature saturating the carbonate ion
buffer
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Flakiness in ocean / atmosphereequilibrium
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Neutralization by CaCO3
CO2 CaCO3 H2O gt Ca2 2 HCO3-
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How long does it take?
Neutralization e-folding timescale
Archer 2005 5-8kyr Lenton 2006 500 - 1000
yr Ridgwell 2007 1-2 kyr Tyrell 2007 2-3
kyr
Pulls the airborne fraction down to 10
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The Silicate Weathering CO2 Thermostat
Volcanic CO2 degassing
CaSiO2 -gt Ca2 SiO2
Weathering function( CO2 )
Ca2 CO3 -gt CaCO3
CaCO3 SiO2 -gt CaSiO2 CO2
Burial Subduction
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The Silicate Weathering CO2 Thermostat
CO2
gt100,000 years
Helps explain Carl Sagans Faint Young Sun
paradox
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Time scale must be longer than this
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Sea Level
Sea Level, m
100
Eocene
40
Myr
ago
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Pliocene
3
Myr
ago
Global Mean T, C
Today
IPCC
5
10
15
20
Forecast
Year 2100
-50
-100
Last Glacial
Maximum

20
kyr
ago
-150
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Methane
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Methane is about here
CO2 is here
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Methane is about here
CO2 is here
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Methane
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Methane
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Earths temperature response toradiative forcing
RF
Climate sensitivity D T / D RF
Time scale 10 yrs
Upper 100m
Thermal bufferof the deepocean Time scale 1000
yrs
DeepOcean
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Shindell, et al 2012
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CO2 vs. CH4
CO2 poses a trap for humanity, because of the
time separation of the cause and the impacts,
which will continue to worsen essentially
forever. Its like an ever-intensifying curse
on our descendents, or planting a cancer.
The climate impacts from CH4 peak and subside
within a human timescale. Good cholesterol
vs. Bad cholesterol?
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1 Trillion tons of C gt 2 C peak warming
Allen et al 2009
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1 Trillion tons of C
Already released 1/2 trillion tons 0.3 from
fuels 0.2 from deforestation Costs (cuts /
year) go up if we wait
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Fossil fuels are mostly coal
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Conclusions
No one has a model or theory of climate that
explains the present but predicts that global
warming wont happen and be significant. The
impacts of global warming from CO2 will last for
millennia (not just a few centuries). The
impacts of short-lived greenhouse gases is
attenuated by the slow response time of Earths
temperature. Lesson from the past Sea level
is 100x more sensitive to Earths temperature
on thousand-plus year timescales than the
forecast for the year 2100.
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