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Insights into Climate Dynamics of the Cretaceous and Paleogene Greenhouse

This study explores the role of palaeogeography in climate dynamics during the Cretaceous and Paleogene periods, investigating the influence of solar, palaeogeographic, and carbon cycle forcings. Using model simulations and data analysis, the study examines the impact of palaeogeography on climate sensitivity and identifies regions with minimal palaeogeographically-driven changes. The findings provide valuable insights into climate dynamics of past greenhouse periods and have implications for understanding future climate change.

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Insights into Climate Dynamics of the Cretaceous and Paleogene Greenhouse

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  1. Modelled insights into climate dynamics of the Cretaceous and Paleogene greenhouseDan 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? • How does palaeogeography influence Climate Sensitivity?

  2. (1) Introduction Last 150 Ma: Major climate trends, + variability + ‘events’ What is the role of solar forcing vs. palaeogeographic (including gateways) forcing vs. carbon cycle forcing? Data from Friedrich et al (2012)

  3. (2) Questions to be addressed • Current paradigm: • Paleogeographical / gateway 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 (including gateways) 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”).

  4. (3) Experimental Design Palaeogeographies provided by Getech and Paul Markwick Paleogeographies 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.

  5. (3b) Experimental Design

  6. (3b) Experimental Design The model: HadCM3L (with vegetation) “state-of-the-art”....not.

  7. (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.

  8. (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 4xCO2 TRIFFID Solar constants Ozone concentrations Lakes No Ice + 2 x CO2 Creation of islands Baratropic stremfunction Ice + 2 x CO2 Ice + 4 x CO2 Simulation spinup – from Alex Farnsworth

  9. (4) Results Global means...

  10. (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. Animations removed

  11. (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. Animations removed

  12. (4) Results Vegetation... e.g. Expansive N and S American deserts in early Cretaceous. ‘Green’ Sahara develops in late Eocene. Animations removed

  13. (4) Results Single sites...

  14. (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

  15. (4) Results Climate Sensitivity

  16. (4) Results Climate Sensitivity 3.3oC 2.8oC 3.0oC 2.8oC 3.0oC 3.2oC 2.5oC

  17. 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.

  18. (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

  19. (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. .

  20. (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@bristol.ac.uk

  21. 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.html

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