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Motivation Experiment aims and description of models Results –

High resolution simulations of Last Glacial Maximum climate over Europe – a solution to discrepancies with observations?. D. Lunt (1) , A. Jost (2) , P. Valdes (1) , A. Abe-Ouchi (3) , M. Kageyama (2) , G. Ramstein, (2).

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Motivation Experiment aims and description of models Results –

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  1. High resolution simulations of Last Glacial Maximum climate over Europe – a solution to discrepancies with observations? D. Lunt (1), A. Jost (2), P. Valdes (1), A. Abe-Ouchi(3) , M. Kageyama(2) , G. Ramstein,(2) • Bristol Research Initiative for the Dynamic Global Environment (BRIDGE), Bristol University, UK • LSCE, Gif-sur Yvette, France • CCSR, Tokyo University, Japan • Motivation • Experiment aims and description of models • Results – • LMDz, CCSR, HadRM compared to observations • Discussion of results • 4) Conclusions and future work d.j.lunt@bristol.ac.uk

  2. 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).

  3. EXPERIMENT AIMS + MODELS USED • Does 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

  4. RESULTS(1) - Tcold LMDz low res, Tcold (LGM-present)

  5. RESULTS(2) - Tcold CCSR, low res, Tcold, M=9.0 M’=11.9 HadAM, low res, Tcold, M=8.4 M’=10.6 LMDz, low res, Tcold, M=6.5 M’=9.6

  6. RESULTS(3) - Tcold HadRM high res, Tcold (LGM-present)

  7. RESULTS(4) - Tcold CCSR, high res, Tcold, M’=12.4 (cf 11.9) HadRM, high res, Tcold, M’=5.9 (cf 10.6) LMDz, high res, Tcold, M’=9.8 (cf 9.6)

  8. 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.

  9. CCSR low res CCSR high res RESULTS(1) - Pann Mean absolute error LMDz low res LMDz high res HadAM low res HadRM high res Reason for wetter LGM in Hadley Centre model: Relatively high CLIMAP SSTs In Mediterranean. Cold air above advected from sea-ice -900mm +900mm

  10. CONCLUSIONS • In 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.

  11. 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.

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