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Modelled insights into climate dynamics of the Cretaceous and Paleogene greenhouse Dan Lunt, Claire Loptson, Alex Farnsworth, Paul Markwick

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Title: Modelled insights into climate dynamics of the Cretaceous and Paleogene greenhouse Dan Lunt, Claire Loptson, Alex Farnsworth, Paul Markwick


1
Modelled insights into climate dynamics of the
Cretaceous and Paleogene greenhouse Dan 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?

2
(1) Introduction
Last 150 Ma Major climate trends, events
What is the role of solar forcing vs.
palaeogeographic forcing vs. carbon cycle forcing?
Data from Friedrich et al (2012)
3
(1) Introduction
CO2 proxies
Palaeogeography
Solar forcing
Maps from Scoteses Paleomap
4
(2a) Previous modelling work (paleogeography)
Real models...
e.g. Westward flow through Tethys.
Luyendyk et al, (1972)
e.g. significant effect on temperature due to
continental area (i.e. sea level), and potential
importance of desert regions.
Energy balance models...
Barron et al (1980)
5
(2a) Previous modelling work (paleogeography)
Atmosphere-only models...
e.g. changes in high latitude land area and
topography most important drivers...
Barron and Washington (1984)
Ocean-only models...
e.g. Eastward flow through Tethys.
Barron and Peterson (1990)
e.g. Eocene (from SH) vs. Miocene (from NH) ocean
overturning
Bice et al (2000)
6
(2a) Previous modelling work (paleogeography)
e.g. Atlantic rifting leads to warming, plus
salinity changes usually interpreted as
signalling middle Cretaceous warmth.
Poulsen et al (2003)
Intermediate complexity models...
e.g. break-up of continent leads to increased
seasonality
Donnadieu et al (2006)
7
(2a) Previous modelling work (paleogeography)
Atmosphere-ocean models...
e.g. modelled Eocene meridional temperature
gradients interpreted as being too great.
Huber and Sloan (2001)
e.g. modelled seasonality too large wrt. CLAMP,
for 3 different Cretaceous palaeogeographies
Spicer et al (2008)
8
(2a) Previous modelling work (CO2)
e.g. Eocene climate sensitivity increases at
higher temperatures due to non-linearities in
both forcing and cloud feedbacks.
Caballero and Huber (in press)
e.g. Cretaceous climate sensitivity enhanced due
to vegetation feedbacks.
Zhou et al (2012)
9
(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
    periods
  • Lack of consistency across simulations
  • Coarse palaeogeographies
  • Models have improved
  • SO
  • What is the role of palaeogeography across the
    Cretaceous/Paleogene?
  • Where can new data be targetted to obtain a
    pure climate signal?
  • How does palaeogeography influence Climate
    Sensitivity? (i.e. state dependency).

10
(3b) Experimental Design
Palaeogeographies provided by Getech and Paul
Markwick
Animation removed.
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.
11
(3b) Experimental Design
12
(3b) Experimental Design
The model HadCM3L (with vegetation) state-of-the
-art....not.
13
(3b) Experimental Design
The model HadCM3L
How good is it for the palaeo?
Lunt et al, Clim. Past (2012) Data compiled by
Tom Dunkley Jones.
14
(3b) Experimental Design (consistent across all
simulations)
Phase 1
Phase 2
Phase 3
Phase 4
50-years
400-years
500-1000 years
57-years
Deep ocean temperature
Pre-industrial CO2 Pre-industrial
SSTs Paleogeography's Uniform Veg
Lakes
4xCO2 TRIFFID Solar constants Ozone
concentrations
No Ice 2 x CO2
Creation of islands Baratropic stremfunction
Ice 2 x CO2
Ice 4 x CO2
Simulation spinup from Alex Farnsworth
15
(4) Results
Global means...
16
(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.
17
(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.
18
(4) Results
Vegetation...
e.g. Expansive N and S American deserts in early
Cretaceous. Green Sahara develops in late
Eocene.
Animation removed.
19
(4) Results
Single sites...
20
(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
21
(4) Results
Climate Sensitivity Only one (two) true
sensitivity Earth System Sensitivity. Either
to (a) Wm-2 or (b) ?CO2 This is neither!
Modellers imagination - Charneyvegetation.
22
(4) Results
Climate Sensitivity
3.3oC
2.8oC
3.0oC
2.8oC
3.0oC
3.2oC
2.5oC
23
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.

24
(5) Future work
CESM simulations
Early Cretaceous grid
Late Cretaceous grid
Early Cretaceous DMS emissions
Modern DMS emissions paleo-tised
Modern DMS emissions
Late Cretaceous DMS emissions
25
(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

Sagoo et al, Phil Trans, in press. Kiehl et al,
Phil Trans, in press. Lunt et al, Phil Trans, in
press. .
26
(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 d.j.lunt_at_bristol.ac
.uk
27
Using the palaeo to inform the future
Early Eocene, 55 - 50 Ma
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.
Mid-Pliocene, 3.3 - 3 Ma
Last Interglacial, 135-130 ka
...future, 2100
http//www.paleo.bris.ac.uk/ggdjl/warm_climates.h
tml
28
(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.
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