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Author: Ganopolski, Andrey × Subject: climate sensitivity ×

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Now showing 1 - 2 of 2
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    The Effect of Obliquity-Driven Changes on Paleoclimate Sensitivity During the Late Pleistocene
    (Hoboken, NJ : Wiley, 2018) Köhler, Peter; Knorr, Gregor; Stap, Lennert B.; Ganopolski, Andrey; de Boer, Bas; van de Wal, Roderik S. W.; Barker, Stephen; Rüpke, Lars H.
    We reanalyze existing paleodata of global mean surface temperature ΔTg and radiative forcing ΔR of CO2 and land ice albedo for the last 800,000 years to show that a state-dependency in paleoclimate sensitivity S, as previously suggested, is only found if ΔTg is based on reconstructions, and not when ΔTg is based on model simulations. Furthermore, during times of decreasing obliquity (periods of land ice sheet growth and sea level fall) the multimillennial component of reconstructed ΔTg diverges from CO2, while in simulations both variables vary more synchronously, suggesting that the differences during these times are due to relatively low rates of simulated land ice growth and associated cooling. To produce a reconstruction-based extrapolation of S for the future, we exclude intervals with strong ΔTg-CO2 divergence and find that S is less state-dependent, or even constant state-independent), yielding a mean equilibrium warming of 2–4 K for a doubling of CO2.
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    Nonlinear climate sensitivity and its implications for future greenhouse warming
    (Washington, DC [u.a.] : Assoc., 2016) Friedrich, Tobias; Timmermann, Axel; Tigchelaar, Michelle; Elison Timm, Oliver; Ganopolski, Andrey
    Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing-referred to as specific equilibrium climate sensitivity (S)-is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth's future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections.