CP Climate of the Past CP Clim. Past 1814-9332 Copernicus Publications Göttingen, Germany 10.5194/cp-9-1761-2013 Assessing the impact of late Pleistocene megafaunal extinctions on global vegetation and climate Brault M.-O. 1 3 Mysak L. A. 1 Matthews H. D. https://orcid.org/0000-0003-3625-390X 2 Simmons C. T. 1 Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Canada Department of Geography, Planning and Environment, Concordia University, Montreal, Canada now at: Department of Geography, McGill University, Montreal, Canada 02 08 2013 9 4 1761 1771 Copyright: © 2013 M.-O. Brault et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://cp.copernicus.org/articles/9/1761/2013/cp-9-1761-2013.html The full text article is available as a PDF file from https://cp.copernicus.org/articles/9/1761/2013/cp-9-1761-2013.pdf

The end of the Pleistocene was a turning point for the Earth system as climate gradually emerged from millennia of severe glaciation in the Northern Hemisphere. The deglacial climate change coincided with an unprecedented decline in many species of Pleistocene megafauna, including the near-total eradication of the woolly mammoth. Due to an herbivorous diet that presumably involved large-scale tree grazing, the mammoth extinction has been associated with the rapid expansion of dwarf deciduous trees in Siberia and Beringia, thus potentially contributing to the changing climate of the period. In this study, we use the University of Victoria Earth System Climate Model (UVic ESCM) to simulate the possible effects of these extinctions on climate during the latest deglacial period. We have explored various hypothetical scenarios of forest expansion in the northern high latitudes, quantifying the biogeophysical effects in terms of changes in surface albedo and air temperature. These scenarios include a Maximum Impact Scenario (MIS) which simulates the greatest possible post-extinction reforestation in the model, and sensitivity tests which investigate the timing of extinction, the fraction of trees grazed by mammoths, and the southern extent of mammoth habitats. We also show the results of a simulation with free atmospheric CO<sub>2</sub>-carbon cycle interactions. For the MIS, we obtained a surface albedo increase and global warming of 0.006 and 0.175 °C, respectively. Less extreme scenarios produced smaller global mean temperature changes, though local warming in some locations exceeded 0.3 °C even in the more realistic extinction scenarios. In the free CO<sub>2</sub> simulation, the biogeophysical-induced warming was amplified by a biogeochemical effect, whereby the replacement of high-latitude tundra with shrub forest led to a release of soil carbon to the atmosphere and a small atmospheric CO<sub>2</sub> increase. Overall, our results suggest the potential for a small, though non-trivial, effect of megafaunal extinctions on Pleistocene climate.

 References Alroy, J.: A multispecies overkill simulation of the end-Pleistocene megafaunal mass extinction. Science, 292, 1893–1896, 2001. Arora, V. K. and Montenegro, A.: Small temperature benefits provided by realistic afforestation efforts, Nat. Geosci., 4, 514–518, 2011. Bala, G., Caldeira, K., Wickett, M., Phillips, T. J., Lobell, D. B., Delire, C., and Mirin, A.: Combined climate and carbon-cycle effects of large-scale deforestation, Proc. Natl. Acad. Sci. USA, 104, 6550–6555, 2007. Barnosky, A. D., Koch, P. L., Feranec, R. S., Wing, S. L., and Shabel, A. B.: Assessing the causes of late Pleistocene extinctions on the continents, Science, 306, 70–75, 2004. Bathiany, S., Claussen, M., Brovkin, V., Raddatz, T., and Gayler, V.: Combined biogeophysical and biogeochemical effects of large-scale forest cover changes in the MPI earth system model, Biogeosciences, 7, 1383–1399, <a href="http://dx.doi.org/10.5194/bg-7-1383-2010">https://doi.org/10.5194/bg-7-1383-2010</a>, 2010. Betts, R. A.: Offset of the potential carbon sink from boreal forestation by decreases in surface albedo, Nature, 408, 187–190, 2000. Bitz, C. M., Holland, M. M., Weaver, A. J., and Eby, M.: Simulating the ice-thickness distribution in a coupled climate model, J. Geophys. Res., 106, 2441–2463, 2001. Bonan, G. B., Pollard, D., and Thompson, S. L.: Effects of boreal forest vegetation on global climate, Nature, 359, 716–718, 1992. Bonan, G. B., Chapin III, F. S., and Thompson, S. L.: Boreal forests and tundra ecosystems as components of the climate system, Clim. Change, 29, 145–167, 1995. Brovkin, V., Levis, S., Loutre, M.-F., Crucifix, M., Claussen, M., Ganopolski, A., Kubatzki, C., and Petoukhov, V.: Stability analysis of the climate-vegetation system in the northern high latitudes, Clim. Change, 57, 119–138, 2003. Brovkin, V., Raddatz, T., Reick, C. H., Claussen, M., and Gayler, V.: Global biogeophysical interactions between forest and climate, Geophys. Res. Lett., 36, L07405, <a href="http://dx.doi.org/10.1029/2009GL037543">https://doi.org/10.1029/2009GL037543</a>, 2009. Chalita, S. and Le Treut, H.: The albedo of temperate and boreal forest and the Northern Hemisphere climate: a sensitivity experiment using the LMD GCM, Clim. Dynam., 10, 231–240, 1994. Claussen, M., Brovkin, V., and Ganopolski, A.: Biogeophysical versus biogeochemical feedbacks of large-scale land-cover change, Geophys. Res. Lett., 28, 1011–1014, 2001. Cox, P.: Description of the "TRIFFID" Dynamic Global Vegetation Model, Met Office, Hadley Centre technical note 24, 2001. Cox, P. M., Betts, R. A., Bunton, C. B., Essery, R. L., Rowntree, P. R., and Smith, J.: The impact of new land surface physics on the GCM simulation of climate and climate sensitivity, Clim. Dynam., 15, 183–203, 1999. Crucifix, M., Betts, R. A., and Hewitt, C. D.: Pre-industrial-potential and Last Glacial Maximum global vegetation simulated with a coupled climate-biosphere model: Diagnosis of bioclimatic relationships, Global Planet. Change, 45, 295–312, 2005. Davin, E. L. and de Noblet-Ducoudré, N.: Climatic impact of global-scale deforestation: radiative versus nonradiative processes, J. Climate, 23, 97–112, 2010. De Deyn, G. B., Cornelissen, J. H., and Bardgett, R. D.: Plant functional traits and soil carbon sequestration in contrasting biomes, Ecol. Lett., 11, 516–531, 2008. Doughty, C. E., Wolf, A., and Field, C. B.: Biophysical feedbacks between the Pleistocene megafauna extinction and climate: The first human-induced global warming?, Geophys. Res. Lett., 37, L15703, <a href="http://dx.doi.org/10.1029/2010GL043985">https://doi.org/10.1029/2010GL043985</a>, 2010. Douville, H. and Royer, J.-F.: Influence of the temperate and boreal forests on the Northern Hemisphere climate in the Météo-France climate model, Clim. Dynam., 13, 57–74, 1997. Eby, M., Zickfeld, K., Montenegro, A., Archer, D., Meissner, K. J., and Weaver, A. J.: Lifetime of anthropogenic climate change: millenial time scales of potential CO<sub>2</sub> and surface temperature perturbations, J. Climate, 22, 2501–2511, 2009. Fanning, A. F. and Weaver, A. J.: An atmospheric energy-moisture balance model: climatology, interpentadal climate change, and coupling to an ocean general circulation model, J. Geophys. Res., 128, 15111–15128, 1996. Foley, J. A., Prentice, I. C., Ramankutty, N., Levis, S., Pollard, D., Sitch, S., and Haxeltine, A.: An integrated biosphere model of land surface processes, terrestrial carbon balance, and vegetation dynamics, Global Biogeochem. Cy., 10, 603–628, 1996. Foley, J. A., Costa, M. H., Delire, C., Ramankutty, N., and Snyder, P.: Green surprise? How terrestrial ecosystems could affect earth's climate, Front. Ecol. Environ., 1, 38–44, 2003. Fraedrich, K., Jansen, H., Kirk, E., and Lunkeit, F.: The Planet Simulator: Green planet and desert world, Meteorol. Z., 14, 305–314, 2005. Gibbard, S., Caldeira, K., Bala, G., Phillips, T. J., and Wickett, M.: Climate effects of global land cover change, Geophys. Res. Lett., 32, L23705, <a href="http://dx.doi.org/10.1029/2005GL024550">https://doi.org/10.1029/2005GL024550</a>, 2005. Gill, J. L., Williams, J. W., Jackson, S. T., Lininger, K. B., and Robinson, G. S.: Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America, Science, 326, 1100–1103, 2009. Grayson, D. K. and Meltzer, D. J.: A requiem for North American overkill, J. Archaeol. Sci., 30, 585–593, 2003. Guthrie, R. D.: New carbon dates like climatic change with human colonization and Pleistocene extinctions, Nature, 441, 207–209, 2006. Heck, P., Lüthi, D., Wernli, H., and Schär, C.: Climate impacts of European-scale anthropogenic vegetation changes: A sensitivity study using a regional climate model, J. Geophys. Res., 106, 7817–7835, 2001. Kabat, P., Claussen, M., Dirmeyer, P. A., Gash, J. H. C., de Guenni, L. B., Meybeck, M., Vörösmarty, C. J., Hutjes, R. W. A., and Lütkemeier, S.: Vegetation, water, humans and the climate: A new perspective on an interactive system, in: Global Change: The IGBP Series, Berlin, Springer, p. 566, 2004. Koch, P. L. and Barnosky, A. D.: Late Quaternary Extinctions: state of the debate, Annu. Rev. Ecol. Evol. Syst., 37, 215–250, 2006. Martin, P. S.: Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of America, Berkely, CA, Univ. of California Press, 2005. Matthews, H. D., Weaver, A. J., Meissner, K. J., Gillett, N. P., and Eby, M.: Natural and anthropogenic climate change: incorporating historical land cover change, vegetation dynamics and the global carbon cycle, Clim. Dynam., 22, 461–479, 2004. Matthews, H. D., Weaver, A. J., and Meissner, K. J.: Terrestrial carbon cycle dynamics under recent and future climate change, J. Climate, 18, 1609–1628, 2005. Meissner, K. J., Weaver, A. J., Matthews, H. D., and Cox, P. M.: The role of land surface dynamics in glacial inception: a study with the UVic Earth System Model, Clim. Dynam., 21, 515–537, 2003. Notaro, M. and Liu, Z.: Statistical and dynamical assessment of vegetation feedbacks on climate over the boreal forest, Clim. Dynam., 31, 691–712, 2008. Otterman, J., Chou, M.-D., and Arking, A.: Effects of nontropical forest cover on climate, J. Clim. Appl. Meteorol., 23, 762–767, 1984. Owen-Smith, N.: Pleistocene extinctions: the pivotal role of megaherbivores, Paleobiol., 13, 351–362, 1987. Pacanowski, R. C.: MOM 2 documentation, user's guide and reference manual, Princeton, GFDL Ocean Group Technical Report, NOAA, GFDL, 232 pp., 1995. Peltier, W. R.: Ice age paleotopography, Science, 265, 195–201, 1994. Petit, J. R., Jouzel, J., Raynaud, D., Barkov, N. I., Barnola, J.-M., Basile, I., Bender, M., Chappellaz, J., Davis, M., Delaygue, G., Delmotte, M., Kotlyakov, V. M., Legrand, M., Lipenkov, V. Y., Lorius, C., Pépin, L., Ritz, C., Saltzman, E., and Stievenard, M.: Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica, Nature, 399, 429–436, 1999. Prentice, I. C., Sykes, M. T., and Cramer, W.: The possible dynamic response of northern forests to global warming, Glob. Ecol. Biogeogr. Lett., 1, 129–135, 1991. Prescott, G. W., Williams, D. R., Balmford, A., Green, R. E., and Manica, A.: Quantitative global analysis of the role of climate and people in explaining late Quaternary megafaunal extinctions, Proc. Natl. Acad. Sci. USA, 109, 4527–4531, 2012. Schmittner, A., Oschlies, A., Matthews, H. D., and Galbraith, E. D.: Future changes in climate, ocean circulation, ecosystems, and biogeochemical cycling simulated for a business-as-usual CO<sub>2</sub> emission scenario until year 4000 Ad, Global Biogeochem. Cy., 22, GB1013, <a href="http://dx.doi.org/10.1029/2007GB002953">https://doi.org/10.1029/2007GB002953</a>, 2008. Simmons, C. T., Mysak, L. A., and Matthews, H. D.: Investigation of carbon dynamics since the Last Glacial Maximum with a model of intermediate complexity. Poster presented at the annual meeting of the American Geophysical Union, San Francisco, USA, 2012. Snyder, P. K., Delire, C., and Foley, J. A.: Evaluating the influence of different vegetation biomes on the global climate, Clim. Dynam., 23, 279–302, 2004. Swann, A. L., Fung, I. Y., Levis, S., Bonan, G. B., and Doney, S. C.: Changes in arctic vegetation amplify high-latitude warming through the greenhouse effect, Proc. Nat. Acad. Sci. USA, 107, 1295–1300, 2010. Thomas, G. and Rowntree, P. R.: The boreal forests and climate, Q. J. R. Meteorol. Soc., 118, 469–497, 1992. Weaver, A. J., Eby, M., Wiebe, E. C., Bitz, C. M., Duffy, P. B., Ewen, T. L., Fanning, A. F., Holland, M. M., MacFadyen, A., Matthews, H. D., Meissner, K. J., Saenko, O., Schmittner, A., Wang, H., and Yoshimori, M.: The UVic Earth System Climate Model: model description, climatology, and applications to past, present and future climates, Atmos. Ocean, 39, 361–428, 2001. Wroe, S., Field, J., Fullagar, R., and Jermin, L. S.: Megafaunal extinction in the late Quaternary and the global overkill hypothesis, in: Alcheringa: An Australasian Journal of Palaeontology, London, Taylor & Francis, 291–331, 2004. Zimov, S. A., Zimov, N. S., Zimova, A. E., Zimova, G. M., Chuprynin, V. I., and Chapin III, F. S.: Carbon storage in permafrost and soils of the mammoth tundra-steppe biome: Role in the global carbon budget, Geophys. Res. Lett., 36, L02502, <a href="http://dx.doi.org/10.1029/2008GL036332">https://doi.org/10.1029/2008GL036332</a>, 2009.