High resolution simulations of Last Glacial Maximum climate over Europe – a solution to discrepancies with

observations?

1) Motivation

2) Experiment aims and description of models

3) Results –

• LMDz, CCSR, HadRM compared to observations

• Discussion of results

4) Conclusions and future work

D. Lunt (1), A. Jost (2), P. Valdes (1), A. Abe-Ouchi(3) , M. Kageyama(2) , G. Ramstein,(2)

(1) Bristol Research Initiative for the Dynamic Global Environment (BRIDGE), Bristol University, UK

(2) LSCE, Gif-sur Yvette, France

(3) CCSR, Tokyo University, Japan

d.j.lunt@bristol.ac.uk

MOTIVATION(previous work by Kageyama et al)

Intercomparison of PMIP model results.

No model simulated enough cooling over Europe at the LGM, compared to pollen data.

Perhaps due to relatively low resolution (also, ice-sheet reconstruction, dust, vegetation changes).

EXPERIMENT AIMS + MODELS USEDDoes increasing the horizontal resolution of climate models improve the agreement with observations of Last Glacial Maximum temperature and precipitation? Use PMIP boundary conditions (CLIMAP SSTs, Peltier ICE4G ice sheets)

LMDz GCM

•Low res 3.75ox2.5o global

•High res 1.0ox0.5o (zoom centered on Paris (!) )

CCSR GCM

•Low res 6.0ox5.0o global

•High res 1.0ox1.0o global

HadAM/HadRM.

•Low res 3.75ox2.5o global.

•High res 0.45ox0.45o (regional model)

LMDz low res present

LMDz high res present

LMDz low res LGM

RESULTS (1) - Tcold

LMDz low res, Tcold (LGM-present)

RESULTS (2) - Tcold

CCSR, low res, Tcold,

M=9.0

M’=11.9

LMDz, low res, Tcold,

M=6.5

M’=9.6

HadAM, low res, Tcold,

M=8.4

M’=10.6

RESULTS (3) - Tcold

HadRM high res, Tcold (LGM-present)

RESULTS (4) - Tcold

CCSR, high res, Tcold,

M’=12.4

(cf 11.9)

LMDz, high res, Tcold,

M’=9.8

(cf 9.6)

HadRM, high res, Tcold,

M’=5.9

(cf 10.6)

DISCUSSION - Tcold

HadRM has the best simulation of Tcold. Why?

Very cold sea-ice in North Atlantic.

Regional model has good representation of structure and intensity of storms. More high-windspeed events – larger surface fluxes – greater cooling. Feedback due to increase in meridional temperature gradient with increasing sea-ice.

RESULTS (1) - Pann

-900mm +900mm

CCSR low res CCSR high res

LMDz low res LMDz high res

HadAM low res HadRM high res

LOW HIGHCCSR 270 230

LMDz 240 260

Had 240 400

Mean absolute error

Reason for wetter LGM in Hadley Centre model:

Relatively high CLIMAP SSTs In Mediterranean. Cold air above advected from sea-ice

CONCLUSIONSIn the Hadley Centre model, agreement with Tcold LGM data is much improved in the regional high res. model compared to standard global model. This is due to very cold sea-ice in North Atlantic, linked to high surface heat fluxes, linked to intense storm activity. Feedback is via increased meridional temperature gradient.

In the same model, precipitation worsens, possibly due to the CLIMAP Mediterranean SSTs, which may be too high.

However, LMDz and CCSR do not show large differences between high and low resolutions. Maybe due to different approach, or ‘critical’ resolution.

“The Last Glacial Maximum climate over Europe: High resolution simulations”, Jost, Lunt,Kageyama, Abe-Ouchi, Peyron, Valdes, and Ramstein, in prep.

FUTURE WORK

Investigate sea-ice issues further – inclusion of ‘leads’.

Validation of sea-ice surface temperatures for the modern.

New interpretation of data – more modern analogues.

Inclusion of a small Alpine ice-cap.

Updated SST reconstructions.