Dan Lunt EGU 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

Dan Lunt EGU 2013Dan Lunt

Introduction – using the palaeo to inform the future

QUALITATIVE INFORMATION

QUANTITATIVE INFORMATION

PALAEO DATAe.g. existence of fossilised leaves in Cretaceous Antarctica

e.g. ice core CO2 records

e.g. proxy reconstructions of temperature and CO2

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

Dan Lunt EGU 2013Dan Lunt

Introduction – using the palaeo to inform the future

QUALITATIVE INFORMATION

QUANTITATIVE INFORMATION

PALAEO DATAe.g. existence of fossilised leaves in Cretaceous Antarctica

e.g. ice core CO2 records

e.g. proxy reconstructions of temperature and CO2

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

Dan Lunt EGU 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

Dan Lunt EGU 2013Friedrich et al (2012) and Zachos et al (2008)

Global temperature evolution over the last ~100 million years

Introduction – Cretaceous and Eocene

Dan Lunt EGU 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

Dan Lunt EGU 2013Dan Lunt

Introduction – Cretaceous and Eocene

CO2 forcing[Honisch et al, 2012]

Solar forcing[Gough, 1981]

Dan Lunt EGU 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?

Dan Lunt EGU 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

Dan Lunt EGU 2013Dan Lunt

CO2 forcing[Honisch et al]

Results – Experimental Design

Dan Lunt EGU 2013Dan Lunt

Results – Cretaceous global mean temperature

Puceat et al, 2003

Dan Lunt EGU 2013Dan Lunt

Results – Cretaceous temperature variations at a single site

Dan Lunt EGU 2013Dan Lunt

Results – Cretaceous/Eocene/modern climate sensitivity

Eocene (4.7 oC) Maasthrichtian (2.5 oC)

Future (4.4 oC)

Dan Lunt EGU 2013Dan Lunt

Conclusions

There is a state dependence of climate through the Cretaceous (~ 1.5 oC).

There is a state dependence of climate sensitivity through the Cretaceous and Eocene (~ 2 oC)

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 oC.

(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.

Dan Lunt EGU 2013Dan Lunt

Introduction – using the palaeo to inform the future

QUALITATIVE INFORMATION

QUANTITATIVE INFORMATION

PALAEO DATAe.g. existence of fossilised leaves in Cretaceous Antarctica

e.g. ice core CO2 records

e.g. proxy reconstructions of temperature and CO2

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

Dan Lunt EGU 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.