Part 6. Current, Past, and Future Climates Chapter 15 Earth’s Climates.
Understanding past climates
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Transcript of Understanding past climates
Understanding past climates
Dick KroonDepartment of Paleoecology and Paleoclimatology
Faculty of Earth and Life SciencesVrije Universiteit
Amsterdam
Why is IODP useful for society?
Paleoclimatology provides a framework for understanding our climate system and may
even lead to climate prediction or not.
Temperature Northern HemisphereReconstruction + measurements scenarios
for future
1000 1200 1400 1600 1800 2000 2100
IPCC 2001
year AD
A geological framework (and thus IODP) is needed to put current anthropogenic warming into a context of climate history.
This is necessary to provide answers to the following questions:• How unique is the current warming as a
response to greenhouse gases? Has it happened before?
• Which feedbacks operate during an extreme warming event?
Why is the current anthropogenic warming dangerous?
modeling experiments to predict the future:
with long-term changes in insolation and greenhouse gas concentrations
H. Renssen and modeling group
METHODS: simulations with ECBilt-CLIO global 3D climate model
ECBilt (Atmospheric model)– quasi-geostrophic equations
– T21 (~5.6° lat-lon), 3 vertical levels
CLIO 3°x 3° lat-lon • Ocean general circulation model
– Primitive equations – free surface– 20 vertical levels
• Sea-ice model– Thermodynamics and dynamics– 3 layers snow-ice model + leads
coupled
H. Renssen
Atmospheric CH4 and CO2 concentrations
500
550
600
650
700
750
-9000 -8000 -7000 -6000 -5000 -4000 -3000 -2000 -1000 0
year
CH
4 c
onc
[ppb
v]
260
265
270
275
280
285
CO
2 c
onc
[ppm
v]
CH4 CO2
Forcing (2)
Not taken into account:
• Volcanism• Changes in solar activity• High-frequency changes in greenhouse gases in period 9,000-250 yr BP• Melting of Laurentide Ice Sheet
Northern Hemispheric annual mean temperature
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
-9000 -8000 -7000 -6000 -5000 -4000 -3000 -2000 -1000 0
time [yr]
°C
present-day level
level at 2100 AD
Simulated Northern Hemisphere annual mean temperature
9k climate 0k climate
Methane hydrate instability possibly amplifiedmillennial-scale climate change during the last glacial
Methane and δ18O in Greenland ice cores
Tertiary pCO2
pCO2 reconstructions from planktonic foraminiferal boron isotope measurements (Pearson
and Palmer 2000)
=> values lower than 500 ppm throughout the Neogene ?
Intensification of N Hem Glaciation
Mid Miocene Antarctic Glaciation
-0.5
0
0.5
1
1.5
13 C
(‰
VP
DB
)C benthic
0 4 8 12 16 20 24 28
2
Eq. Atlantic
N Atlantic
Southern Ocean
Eq. Pacific
Sediment observations
δ13C in benthic foraminifers
varying gradients between
North Atlantic, South
Atlantic, and Southern
Ocean are interpreted in
terms of the strength of
thermohaline overturning
benthic δ13C data from Wright and Miller
1996, Shackleton + Crowhurst 1997,
Billups 2002
PETM
Evidence for methane hydrate instability during PETM:• 3‰ excursion in 13C in all reservoirs• pronounced dissolution of carbonate• 1 to 8°C increase in ocean temperatures (18O, Mg/Ca)
0
1
2
3
4
5
6
10 15 20 25 30
G. ruber pinkG. ruber whiteG. sacculiferG. sacculifer with sacN. dutertreiP. obliquiloculataG. conglobatusG. inflataG. truncatulinoidesG. hirsutaG. crassiformisall species
18O calcification temperature (oC)
Mg/Ca= 0.38± 0.02 exp (0.09±0.003)*T)
Anand et al., Paleoceanography,
2003.
Mg/Ca in planktonic foraminifera
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
293.60 294.10 294.60 295.10 295.60 296.10
ODP Site 1263depth (mcd)
-0.500
0.000
0.500
1.000
1.500
2.000
2.500
bulk measurements
A. soldadoensis
Lourens, Sluijs, Kroon en Leg 208 Scientific Party
Lourens, Sluijs, Kroon and Leg 208 Scientific Party
What is a gas hydrate?Crystalline solid constituting of gas molecules, usually methane, surrounded by a cage of water molecules
• IODP gives the paleoclimate community the opportunity to make an attempt to find the cause of this event, and others, as well as the consequences of rapid greenhouse warming.
• PETM scenario is analogue for our future climate. Studying this event and others may tell us what may happen with our future climate. Is methane a potential source for a positive feedback?