Clim. Past Discuss., 7, 1-46, 2011
www.clim-past-discuss.net/7/1/2011/
doi:10.5194/cpd-7-1-2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Impact of CO2 and climate on the Last Glacial Maximum vegetation
M.-N. Woillez1, M. Kageyama1, G. Krinner2, N. de Noblet-Ducoudré1, N. Viovy1, and M. Mancip1
1LSCE/IPSL INSU, UMR 8212, CE Saclay, l'Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
2LGGE, UMR CNRS 5183, 54 rue Molière, 38402 St. Martin d'Hères Cedex, France

Abstract. Vegetation reconstructions from pollen data for the Last Glacial Maximum (LGM), 21 kyr ago, reveal lanscapes radically different from the modern ones, with, in particular, a massive regression of forested areas in both hemispheres. Two main factors have to be taken into account to explain these changes in comparison to today's potential vegetation: a generally cooler and drier climate and a lower level of atmospheric CO2. In order to assess the relative impact of climate and atmospheric CO2 changes on the global vegetation, we simulate the potential modern vegetation and the glacial vegetation with the dynamical global vegetation model ORCHIDEE, driven by outputs from the IPSL_CM4_v1 atmosphere-ocean general circulation model, under modern or glacial CO2 levels for photosynthesis. ORCHIDEE correctly reproduces the broad features of the glacial vegetation. Our modelling results support the view that the physiological effect of glacial CO2 is a key factor to explain vegetation changes during glacial times. In our simulations, the low atmospheric CO2 is the only driver of the tropical forests regression, and explains half of the response of temperate and boreal forests to glacial conditions. Our study shows that the sensitivity to CO2 changes depends on the background climate over a region, and also depends on the vegetation type, needleleaf trees being much more sensitive than broadleaf trees in our model. This difference of sensitivity leads to a dominance of broadleaf types in the remaining simulated forests, which is not supported by pollen data, but nonetheless suggests a potential impact of CO2 on the glacial vegetation assemblages. It also modifies the competitivity between the trees and makes the amplitude of the response to CO2 dependent on the initial vegetation state.

Citation: Woillez, M.-N., Kageyama, M., Krinner, G., de Noblet-Ducoudré, N., Viovy, N., and Mancip, M.: Impact of CO2 and climate on the Last Glacial Maximum vegetation, Clim. Past Discuss., 7, 1-46, doi:10.5194/cpd-7-1-2011, 2011.
 
Search CPD
Discussion Paper
    XML
    Citation
    Final Revised Paper
    Share