what is the role of palaeogeography across the cretaceous and paleogene?
DESCRIPTION
Modelled insights into climate dynamics of the Cretaceous and Paleogene greenhouse Dan Lunt, Claire Loptson, Alex Farnsworth, Paul Markwick. What is the role of palaeogeography across the Cretaceous and Paleogene? Where can new data be targetted to obtain a ‘pure’ climate signal? - PowerPoint PPT PresentationTRANSCRIPT
ICP, Sitges, 2013
Modelled insights into climate dynamics of the Cretaceous and
Paleogene greenhouseDan Lunt, Claire Loptson, Alex Farnsworth, Paul Markwick
(1) What is the role of palaeogeography across the Cretaceous and Paleogene?
(2) Where can new data be targetted to obtain a ‘pure’ climate signal?
(3) How does palaeogeography influence Climate Sensitivity?
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Data from Friedrich et al (2012)
(1) Introduction
What is the role of solar forcing vs. palaeogeographic forcing vs. carbon cycle forcing?
Last 150 Ma:
Major climate trends, + ‘events’
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(1) Introduction
CO2 proxies
Solar forcing
Palaeogeography
Maps from Scotese’s ‘Paleomap’
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(2a) Previous modelling work (paleogeography)
Luyendyk et al, (1972)
Barron et al (1980)
‘Real’ models...
Energy balance models...
e.g. Westward flow through Tethys.
e.g. significant effect on temperature due to continental area (i.e. sea level), and potential importance of desert regions.
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Barron and Peterson (1990)
Barron and Washington (1984)
Bice et al (2000)
Atmosphere-only models...
Ocean-only models...
(2a) Previous modelling work (paleogeography)
e.g. changes in high latitude land area and topography most important drivers...
e.g. Eastward flow through Tethys.
e.g. Eocene (from SH) vs. Miocene (from NH) ocean overturning
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e.g. Atlantic rifting leads to warming, plus salinity changes usually interpreted as signalling middle Cretaceous warmth.
Donnadieu et al (2006)
Poulsen et al (2003)
Intermediate complexity models...
(2a) Previous modelling work (paleogeography)
e.g. break-up of continent leads to increased seasonality
ICP, Sitges, 2013Spicer et al (2008)
Huber and Sloan (2001)
Atmosphere-ocean models...
(2a) Previous modelling work (paleogeography)
e.g. modelled seasonality too large wrt. CLAMP, for 3 different Cretaceous palaeogeographies
e.g. modelled Eocene meridional temperature gradients interpreted as being too great.
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e.g. Cretaceous climate sensitivity enhanced due to vegetation feedbacks. Zhou et al (2012)
(2a) Previous modelling work (CO2)
Caballero and Huber (in press)
e.g. Eocene climate sensitivity increases at higher temperatures – due to non-linearities in both forcing and cloud feedbacks.
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(3a) Questions to be addressed
Current paradigm:
Paleogeographical changes less important than greenhouse gas forcing.
BUT:
Work mostly focussed on a limited number of time periodsLack of consistency across simulationsCoarse palaeogeographiesModels have improved
SO:
(1)What is the role of palaeogeography across the Cretaceous/Paleogene?(2)Where can new data be targetted to obtain a ‘pure’ climate signal?(3)How does palaeogeography influence Climate Sensitivity? (i.e. “state dependency”).
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(3b) Experimental DesignPalaeogeographies provided by Getech and Paul Markwick
Created using similar techniques to those outlined in Markwick (2007), based on published lithologic, tectonic and fossil studies, the lithologic databases of the Paleogeographic Atlas Project (University of Chicago), and deep sea (DSDP/ODP) data. Extensively updated from Markwick (2007), e.g. bathymetry, new rotations, more underlying data.
Animation removed.
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(3b) Experimental Design
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(3b) Experimental Design
The model: HadCM3L (with vegetation)“state-of-the-art”....not.
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(3b) Experimental DesignThe model: HadCM3L
How good is it for the palaeo?
Lunt et al, Clim. Past (2012)
Data compiled by Tom Dunkley Jones.
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Phase 1 Phase 2 Phase 3 Phase 4D
eep
ocea
n te
mpe
ratu
re
50-years 400-years 57-years 500-1000 years
Pre-industrial CO2
Pre-industrial SSTsPaleogeography'sUniform Veg
Lakes4xCO2
TRIFFIDSolar constantsOzone concentrations
Creation of islandsBaratropic
stremfunction
No Ice + 2 x CO2
Ice + 2 x CO2
Ice + 4 x CO2
(3b) Experimental Design (consistent across all simulations)
Simulation spinup – from Alex Farnsworth
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(4) Results
Global means...
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(4) Results
SSTs...
e.g.Maximum warmth shifts from W. Pacific to E. Indian ocean in Late Eocene.
Zonal mean relatively constant.
ENSO is a constant feature.
Winter Arctic and Southern Ocean seaice for all time periods.
Animation removed.
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(4) Results
Regions of deep water formation...
e.g.N. Pacific deep water formation in earliest Cretaceous, gone by Middle Cretaceous.
Mid and late Cretaceous and early Eocene little mixing.
North Atlantic deep water formation kicks off ~40 Ma.
Animation removed.
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(4) Results
Vegetation...
e.g.Expansive N and S American deserts in early Cretaceous.
‘Green’ Sahara develops in late Eocene.
Animation removed.
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(4) Results
Single sites...
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(4) Results
Implications for site targetting...Where are the locations with least paleography-related change; i.e. Where to go for a ‘pure’ CO2 signal:
Marine Terrestrial
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(4) Results
Climate Sensitivity Only one (two) ‘true’ sensitivity – Earth System Sensitivity. Either to (a) Wm-2 or (b) ΔCO2
This is neither! Modellers’ imagination - ‘Charney’+vegetation.
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(4) Results
Climate Sensitivity
3.3oC 2.8oC 3.0oC 2.8oC
3.0oC 3.2oC 2.5oC
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Summary
Cretaceous and Paleogene simulations broadly support the paradigm that carbon cycle dominates over palaeogeography forcing.
BUT, at single sites, the temperature changes due to palaeogeography alone can be very large.
AND, other aspects of the system, such as ocean circulation and vegetation, can also show very large palaeogeographically-driven changes.
Simulations can point to where a ‘pure’ CO2 signal could be obtained.
Climate Sensitivity is a function of palaeography, varying by 30% through the late and mid Cretaceous.
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(5) Future work
CESM simulations
Early Cretaceous grid Late Cretaceous grid
Modern DMS emissionsModern DMS emissions“paleo-tised”
Early Cretaceous DMS emissions
Late Cretaceous DMS emissions
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(5) Future work
NERC project: Cretaceous-Paleocene-Eocene: Exploring Climate and Climate Sensitivity
Complete CO2 sensitivities
Ice sheets [e.g. role of CO2, gateways and ice sheets at E-O boundary]
Model internal parameter sensitivity studies.
Data compilations (Stuart Robinson, Oxford). Back-out model-derived CO2 record
Equivalent future simulations
Sagoo et al, Phil Trans, in press.
Kiehl et al, Phil Trans, in press.
Lunt et al, Phil Trans, in press.
.
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(5) Future work
Complete Neogene simulations. Role of orbital forcing
PMIP working group on ‘pre-Pliocene climates’
Joint venture between data and modelling communities
Model output available.Email: [email protected]
ICP, Sitges, 2013Dan Lunt
“Warm Climates of the Past – A lesson for the future?”
Special Issue of Phil Trans A
All papers now ‘in press’
Including contributions from:Badger, DeConto, Dowsett, Foster, Hansen, Haywood, John, Kiehl, Lunt, Otto-Bliesner, Pagani, Pancost, Pearson, Sagoo, Valdes, Zachos, Zeebe, Zhang.
Early Eocene, ~55 - 50 Ma
Mid-Pliocene, ~3.3 - 3 Ma
Last Interglacial, 135-130 ka
...future, 2100
Using the palaeo to inform the future
http://www.paleo.bris.ac.uk/~ggdjl/warm_climates.html
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(4) Results
Precipitation...
e.g.Amazon desiccates in late Oligocene.
East Asian monsoon system initiates in middle Eocene.
North Atlantic storm tracks intensify in late Eocene.
Animation removed.