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 CO₂-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 CO₂ 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 CO₂ increase. Overall, our results suggest the potential for a small, though non-trivial, effect of megafaunal extinctions on Pleistocene climate

Abstract. In this paper, we describe the development and application of a new spatially explicit weathering scheme within the University of Victoria Earth System Climate Model (UVic ESCM). We integrated a dataset of modern-day lithology with a number of previously devised parameterizations for weathering dependency on temperature, primary productivity, and runoff. We tested the model with simulations of future carbon cycle perturbations, comparing a number of emission scenarios and model versions with each other and with zero-dimensional equivalents of each experiment. Overall, we found that our two-dimensional weathering model versions were more efficient in restoring the carbon cycle to its pre-industrial state following the pulse emissions than their zero-dimensional counterparts; however, in either case the effect of this weathering negative feedback on the global carbon cycle was small on timescales of less than 1000 years. According to model results, the largest contribution to future changes in weathering rates came from the expansion of tropical and mid-latitude vegetation in grid cells dominated by weathering-vulnerable rock types, whereas changes in temperature and river runoff had a more modest direct effect. Our results also confirmed that silicate weathering is the only mechanism that can lead to a full recovery of the carbon cycle to pre-industrial levels on multimillennial timescales.

We examine the importance of the rock weathering feedback mechanism during the last deglacial period (∼16 000-4000 BCE) using an Earth system model of intermediate complexity (the University of Victoria Earth System Climate Model (UVic ESCM)) with four box-model parameterizations of terrestrial weathering. The deglacial climate change is driven by changes in orbital parameters, ice core reconstructions of atmospheric CO 2 variability, and prescribed removal of continental ice sheets. Over the course of the 12 000 year simulation period, increases in weathering provide a mechanism that slowly removes CO 2 from the atmosphere, in opposition to the observed atmospheric CO 2 increase during this period. These processes transfer both carbon and alkalinity to the ocean, the combination of which results in as much as a 1000 Pg C increase in total ocean carbon, relative to a control simulation with constant weathering. However, the rapid expansion of northern hemisphere vegetation introduces a significant uncertainty among the weathering parameterizations. Further experiments to test the individual impacts of weathering dissolved inorganic carbon and alkalinity fluxes on ocean biogeochemistry suggest that the worldwide distribution of rock types and the ratio of carbonate to silicate weathering may be crucially important in obtaining an accurate estimate of changes in global weathering rates.

The end of the Pleistocene marked a turning point for the Earth system as climate gradually emerged from millennia of severe glaciation in the Northern Hemisphere. It is widely acknowledged that the deglacial climate change coincided with an unprecedented decline in many species of large terrestrial mammals, including the near-total eradication of the woolly mammoth. Due to an herbivorous diet that presumably involved large-scale tree grazing, the mammoth expansion would have accelerated the expansion of dwarf deciduous trees in Siberia and Beringia, thus 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 megafaunal extinctions on Pleistocene climate change. We have explored various hypothetical scenarios of forest expansion in the Northern Continents, quantifying the regional and global biogeophysical effects in terms of changes in surface albedo and air temperature. In particular, we focus our attention on a Maximum Impact Scenario (MIS) which simulates the greatest possible post-extinction reforestation in the model. More realistic experiments include sensitivity tests based on the timing of extinction, the fraction of trees grazed by mammoths, and the size of mammoth habitats. We also show the results of a simulation with free (non-prescribed) atmospheric CO₂. For the MIS, we obtained a surface albedo increase of 0.006, which resulted in a global warming of 0.175 °C. 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 CO₂ 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 CO₂ increase. Overall, our results suggest the potential for a small, though non-trivial, effect of megafaunal extinctions on Pleistocene climate change

Abstract. In this paper, we describe the development and application of a new spatially-explicit weathering scheme within the University of Victoria Earth System Climate Model (UVic ESCM). We integrated a dataset of modern-day lithology with a number of previously devised parameterizations for weathering dependency on temperature, primary productivity, and runoff. We tested the model with simulations of future carbon cycle perturbations, comparing a number of emission scenarios and model versions with each other and with zero-dimensional equivalents of each experiment. Overall, we found that our two-dimensional weathering model versions were more efficient in restoring the carbon cycle to its pre-industrial state following the pulse emissions than their zero-dimensional counterparts; however, in either case the effect of this weathering negative feedback on the global carbon cycle was small on timescales of less than 1000 years. According to model results, the largest contribution to future changes in weathering rates came from the expansion of tropical and mid-latitude vegetation in grid cells dominated by weathering-vulnerable rock types, whereas changes in temperature and river runoff had a more modest direct effect. Our results also confirmed that silicate weathering is the only mechanism that can lead to a full recovery of the carbon cycle to pre-industrial levels on multi-millennial timescales.