Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 4 6 2008 10.5194/cpd-4-1319-2008 http://www.clim-past-discuss.net/4/1319/2008/ http://www.clim-past-discuss.net/4/1319/2008/cpd-4-1319-2008.html http://www.clim-past-discuss.net/4/1319/2008/cpd-4-1319-2008.pdf 1319 1326 2008-12-22 Comment on "Aerosol radiative forcing and climate sensitivity deduced from the Last Glacial Maximum to Holocene transition", by P. Chylek and U. Lohmann, Geophys. Res. Lett., 2008 J. C. Hargreaves J. D. Annan Frontier Research Centre for Global Change, JAMSTEC 3173-25 Showamachi, Kanazawa-ku, Yokohama City, Kanagawa 236-0001, Japan In a recent paper, Chylek and Lohmann (2008) used data from the Vostok ice core together with simple energy balance arguments to simultaneously estimate both the dust radiative forcing effect and the climate sensitivity, generating surprisingly high and low values for these respective parameters. However, their results depend critically on their selection of single unrepresentative data points from time series which exhibit a large amount of short-term variability, and are highly unstable with respect to other arbitrarily selected data points. When temporal averages are used in accordance with accepted norms within the paleoclimate community, the results obtained are entirely unremarkable and in line with previous analyses. Chylek, P. and Lohmann, U.: Aerosol radiative forcing and climate sensitivity deduced from the Last Glacial Maximum to Holocene transition, Geophys. Res. Lett., 35, L04804, 1–5, doi:10.1029/2007GL032759, 2008. Claquin, T., Roelandt, C., Kohfeld, K E., Harrison, S P., Tegen, I., Prentice, I C., Balkanski, Y., Bergametti, G., Hansson, M., Mahowald, N., Rodhe, H., and Schulz, M.: Radiative forcing of climate by ice-age atmospheric dust, Clim. Dynam., 20, 193–202, 2003. Crucifix, M.: Does the Last Glacial Maximum constrain climate sensitivity, Geophys. Res. Lett, 33, L18701, doi:10.1029/2006GL027137, 2006. Hansen, J., Lacis, A., Ruedy, R., Sato, M., and Wilson, H.: How sensitive is the world's climate?, Natl. Geog. Soc. Res. Exploration, 9, 142–158, 1993. Hargreaves, J C., Abe-Ouchi, A., and Annan, J D.: Linking glacial and future climates through an ensemble of GCM simulations, Clim. Past, 3, 77–87, 2007. Kucera, M., Rosell-Melé, A., Schneider, R., Waelbroeck, C., and Weinelt, M.: Multiproxy approach for the reconstruction of the glacial ocean surface (MARGO), Quaternary Sci. Rev., 24, 813–819, 2005. Mix, A., Bard, E., and Schneider, R.: Environmental processes of the ice age: land, oceans, glaciers (EPILOG), Quaternary Sci. Rev., 20, 627–657, 2001. Petit, J., Jouzel, J., Raynaud, D., Barkov, N., Barnola, J., Basile, I., Bender, M., Chappellaz, J., Davis, M., Delaygue, G., et~al.: Climate and atmospheric history of the past 420 000 years from the Vostok ice core, Antarctica, Nature, 399, 429–436, 1999. Schneider von Deimling, T., Held, H., Ganopolski, A., and Rahmstorf, S.: Climate sensitivity estimated from ensemble simulations of glacial climate, Clim. Dynam., 27, 149–163, 2006. Solomon, S., Qin, D., Manning, M., Chen, Z., et al.: Climate change 2007: The physical science basis, Contribution of the Working Group I to the Four th Assessment Report of the Intergovernmental Panel on Climate Change, Summary for Policy Makers, p. 12 and p. 749, 2007.