1. Dan LuntEGU 2013Dan Lunt Can Cretaceous and Eocene Data Inform Estimates of Future Climate Sensitivity? Dan Lunt, Claire Loptson, Paul Markwick Introduction Using the palaeo to inform the future The Cretaceous and Eocene Questions to be addressed Results Experimental Design Results Summary and future directions

2. Dan LuntEGU 2013Dan Lunt Introduction – using the palaeo to inform the future QUALITATIVE INFORMATIONQUANTITATIVE INFORMATION PALAEO DATA e.g. existence of fossilised leaves in Cretaceous Antarctica e.g. ice core CO 2 records e.g. proxy reconstructions of temperature and CO 2 provide estimates of past climate sensitivity [see Rohling et al, 2012] PALAEO MODEL- DATA COMPARISONS e.g. model-data comparisons reveal model strengths and weaknesses e.g. weighting future model simulations according to palaeo model-data comparisons + analogues and representation of long-term feedbacks in models

3. Dan LuntEGU 2013Dan Lunt Introduction – using the palaeo to inform the future QUALITATIVE INFORMATIONQUANTITATIVE INFORMATION PALAEO DATA e.g. existence of fossilised leaves in Cretaceous Antarctica e.g. ice core CO 2 records e.g. proxy reconstructions of temperature and CO 2 provide estimates of past climate sensitivity [see Rohling et al, 2012] PALAEO MODEL- DATA COMPARISONS e.g. model-data comparisons reveal model strengths and weaknesses e.g. weighting future model simulations according to palaeo model-data comparisons + analogues and representation of long-term feedbacks in models

4. Dan LuntEGU 2013Dan Lunt Warm Climates of the Past – A lesson for the future? Special Issue of Phil Trans A All papers now in press Including contribtions from: DeConto, Dowsett, Foster, Hansen, Haywood, Kiehl, Lunt, Otto-Bliesner, Pagani, Pancost, Pearson, Valdes, Zachos, Zeebe. Early Eocene, ~55 - 50 Ma Mid-Pliocene, ~3.3 - 3 Ma Last Interglacial, 135-130 ka...future, 2100 Introduction – using the palaeo to inform the future

5. Dan LuntEGU 2013 Friedrich et al (2012) and Zachos et al (2008) Global temperature evolution over the last ~100 million years Introduction – Cretaceous and Eocene

6. Dan LuntEGU 2013 mid-Cretaceous, ~ 100 million years ago © Bob Nicholls. A depiction of Alexander Island, Antarctica, during the Cretaceous early Eocene, ~50 million years ago Introduction – Cretaceous and Eocene Lunt et al, 2012; Data compiled by Tom Dunkley Jones

7. Dan LuntEGU 2013Dan Lunt Introduction – Cretaceous and Eocene CO 2 forcing [Honisch et al, 2012] Solar forcing [Gough, 1981]

8. Dan LuntEGU 2013Dan Lunt Introduction – Cretaceous and Eocene Research Questions.... (1)How does baseline climate change through these deep time periods? (2)How does Cretaceous/Eocene climate sensitivity compare with modern? (3) What are the implications of the above for proxy reconstructions of climate sensitivity at specific core sites?

9. Dan LuntEGU 2013Dan Lunt Results – Experimental Design HadCM3L (3.75 x 2.5 degrees in atmosphere and ocean) Initial ocean condition = idealised cosine in temperature and salinity; ocean at rest TRIFFID dynamic vegetation

10. Dan LuntEGU 2013Dan Lunt CO 2 forcing [Honisch et al] Results – Experimental Design

11. Dan LuntEGU 2013Dan Lunt Results – Cretaceous global mean temperature Puceat et al, 2003

12. Dan LuntEGU 2013Dan Lunt Results – Cretaceous temperature variations at a single site

13. Dan LuntEGU 2013Dan Lunt Results – Cretaceous/Eocene/modern climate sensitivity Eocene (4.7 o C)Maasthrichtian (2.5 o C) Future (4.4 o C)

14. Dan LuntEGU 2013Dan Lunt Conclusions There is a state dependence of climate through the Cretaceous (~ 1.5 o C). There is a state dependence of climate sensitivity through the Cretaceous and Eocene (~ 2 o C) For these time periods.... (1) Inferring climate trends from single paleo data points is dangerous. Depending on region, the error (even after correcting for paleolat/lon) can be as much as 8 o C. (2) Inferring climate sensitivity from paleo data is dangerous, Depending on time period, the error (even if you can estimate the global mean and forcing correctly), can be as much as x2.

15. Dan LuntEGU 2013Dan Lunt Introduction – using the palaeo to inform the future QUALITATIVE INFORMATIONQUANTITATIVE INFORMATION PALAEO DATA e.g. existence of fossilised leaves in Cretaceous Antarctica e.g. ice core CO 2 records e.g. proxy reconstructions of temperature and CO 2 provide estimates of past climate sensitivity [see Rohling et al, 2012] PALAEO MODEL- DATA COMPARISONS e.g. model-data comparisons reveal model strengths and weaknesses e.g. weighting future model simulations according to palaeo model-data comparisons + analogues and representation of long-term feedbacks in models

16. Dan LuntEGU 2013Dan Lunt Future Work Much still to do.... Complete matrix of 2x and 4x simulations through Cretaceous to modern. Ensure full consistency between all simulations. Explore other uncertainties (e.g. parametric (ensembles), structural (e.g. CCSM), boundary conditions...etc ) Model-data comparisons where possible. Then....possible weighting of future simulations + (most importantly??!!) Process-based understanding of simulations.