Greenhouse gases in the Quaternary: constraining sources, sinks, feedbacks and surprises Eric Wolff...
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![Page 1: Greenhouse gases in the Quaternary: constraining sources, sinks, feedbacks and surprises Eric Wolff 1 and the QUEST-DESIRE team 1. British Antarctic Survey,](https://reader036.fdocuments.in/reader036/viewer/2022062619/5515e34f55034638038b4d0c/html5/thumbnails/1.jpg)
Greenhouse gases in the Quaternary: constraining sources, sinks, feedbacks and surprises
Eric Wolff1 and the QUEST-DESIRE team1. British Antarctic Survey, High Cross, Madingley Road,
Cambridge CB3 0ET, UK
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Why palaeo greenhouse gases?
• How do recent changes compare with natural variability?
• Can we understand natural cycles? – important if we want to underpin estimates of (future) feedbacks
• Does the past constrain the likelihood of “high impact, low probability” events (surprises)?
• How did Earth respond to high CO2 climates?• Can we find analogues for large carbon releases in
the past, to test effects and recovery?
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Plan for today
• Set the scene by presenting the evidence
• Challenge the AIMES community to understand (at process level) the records
• Briefly consider which aspects of the past are most relevant to the future
• Muse on the extent to which the Quaternary Earth System was deterministic
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Recent past – other GHG
240
280
320
1000 1200 1400 1600 1800 2000Age of air / years AD
N2O
/ pp
bv
0
600
1200
1800
CH
4 /
ppbv
280
320
360
CO
2 /
ppm
v
Etheridge et al 1996MacFarling Meure et al 2006
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500
1000
1500
CH
4 /
pp
bv
250
300
350
0200040006000800010000
South Pole flasksLaw Dome (Etheridge et al., 1996)Dome C ice (Fluckiger et al., 2002)
Age / years before 1950 AD
CO
2 /
pp
mv
Greenhouse gases over the Holocene (10 kyr)
Natural or anthropogenic?Ruddiman 2003 (Clim. Change, 61, 261-293)
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European Project for Ice Coring in Antarctica (EPICA)
Dome C75ºS; 3233 m aslMean T:-54.5ºCCore to 3270 m
0km 1 ,000km 2 ,000km
80S°
70S°
60S°
Vo sto k
Do m e F
Ta ylo rDo m e
Byrd
Dro nn ingM a ud La nd
Sip le Do m e
Do m e CLa w Do m e
Be rkne rIsla nd
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-10
-5
0
5
0 200 400 600 800
Age / thousands of years before present
Est
imat
ed D
ome
C
tem
pera
ture
diff
eren
ce / C
Estimated Antarctic temperature(based on water isotopes)
EPICA Community Members, Nature, 429, 623-628, 2004;Jouzel et al., Science, 2007
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What does CO2 do in a changing climate?
- CO2 responsible for 30-50% of the glacial-interglacial warming- probably controlled mainly through processes in the Southern Ocean
200
250
300Lüthi et al., 2008
CO
2 / p
pmv
-10
-5
0
5
0 200 400 600 800Age / EDC3 ka bp (1950)
Est
imat
ed
Dom
e C
te
mpe
ratu
re d
iffer
enc
e / C
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CO2 in the last glacial
Ahn and Brook 2008
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Dome C detailed CO2
Monnin et al (2001)
Science 291, 112-114
Phasing is consistent with CO2 as an amplifier
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13CO2
Lourantou et al, GBC, In Press (2010)
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Estimates courtesy of Andy Ridgwell
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But we are out of the range of the last 800 ka
150
200
250
300
350
400
0 200 400 600 800Age / ka (b1950)
CO
2 /
pp
mv
Lüthi et al., Nature 2008 (EPICA gas consortium)
• In rate as well as concentration:– Fastest multicentennial rate in last termination was ~20 ppmv in
1000 years
– 20 ppmv increase in last 11 years
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CH4
-450
-430
-410
-390
-370
0 200 400 600 800
Jouzel et al 2007
9C
COLD
WARM
Age / EDC3 ka before present
D /
‰
200
400
600
800
1730
Loulergue et al, 2008, Nature
CH
4 /
ppbv
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But the late Pleistocene holds no analogue for the present
-450
-430
-410
-390
-370
0 200 400 600 800
Jouzel et al 2007
9C
COLD
WARM
Age / EDC3 ka before present
D /
‰
600
1200
1800
Loulergue et al, 2008, Nature
CH
4 /
ppbv
And natural changes are dwarfed by the anthropogenic influence
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Rapid events in CH4
300
400
500
600
700
10 20 30 40 50 60 70Age / ka b2k, converted to GICC05
CH
4 /
ppbv
-45
-40
-35
198
18O
/ ‰
Gre
enla
nd
tem
pera
ture
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300
400
500
600
700
0 200 400 600
Vostok + Dome C data
Age / kyr BP
CH
4 /
pp
bv
300
400
500
600
700
0 10000 20000 30000 40000
GRIP/NGRIP
Age / GICC05 yrs BP
CH
4 /
pp
bv
Methane: the rapid jumps account for much of the g-ig change
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Causes of change (CH4)
Sources• Wetlands
– Northern– Tropical
• Methane hydrates• Biomass burning• Others (vegetation,….)
Sinks• OH change
• Temperature• Water vapour• Competition
(VOCs)
Isotopic evidence suggests no major role for hydrates
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δD of CH4Sowers, Science
2006Concludes marine clathrates are not important for these warming events
No evidence of fossil 14C at transitionLarge blocks from Pakitsoq, Greenland. Petrenko et al., 2009, Science
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3-box modelDallenbach et al, GRL, 2000
Combining Dallenbach et al (GRL 2000) and Brook et al (GBC 2000), you would conclude:
Interhemispheric differences
Tropics North
DO cold-warm
Bolling/Allerod to YD
LGM to preBoreal
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13CH4 - termination ILGM 13CH4 ~3.5 ‰ heavier than Holocene
rapid 13CH4 variations during Bolling/Alleroed -Younger Dryas
also slow changes during LGM and early Holocene when CH4 constant
D 20 ‰ heavier in LGM (Sowers, 2006)
Data not really in agreement with conclusions of Schaefer et al (2006)
Fischer et al., Nature 452, 864 (2008)
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Glacial/interglacial CH4 source changes
10 Variables:
5(6) potenial preindustrial sources with different isotopic signature
1 atmospheric lifetime
3 different sinks with different contributions
4 Constraints:
CH4 concentration North & South
D(CH4) North
13CH4 South
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Isotopic constraints
• Box model to estimate range of likely emissions and lifetimes in different time periods
• Relatively minor changes in isotopic content suggest changes in hydrates and biomass burning emissions were modest
• Concludes that main changes are in boreal wetlands and in atmospheric lifetime
• But conclusion on biomass burning seems at odds with terrestrial evidence and lifetime changes are hard to explain (see Levine talk)
• Also the wetland response seems stronger than bottom-up models would predict
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Last interglacial – how did CH4 react to Arctic warmth?
-420
-390
EPICA Dome C
D /
‰
-45
-40
-35
0 50 100 150
NGRIP
Age / ka b1950
18O
/ ‰
300
400
500
600
700
CH
4 /
pp
bv
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Summary• Ice cores show us the unprecedented extent and
rate of the recent increase in greenhouse gases and therefore radiative forcing
• Large changes in Quaternary challenge us to understand natural cycles and test our knowledge of feedbacks (especially wrt ocean carbon and wetland methane)
• Last interglacial might be used to seek reassurance against large methane releases under warming
• For anything approaching an analogue for a world with higher CO2 we will have to tackle the harder questions posed by older climates
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How deterministic is this system?
400
600
800 Loulergue et al 2008
CH
4 /
ppb
v
200
250
300Luethi et al 2008
CO
2 /
ppm
v
-440
-410
-380
0 200 400 600 800
Jouzel et al 2007
9C
COLD
WARM
Age / EDC3 ka before present
D /
‰
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Thank you