State‐Dependence of the Climate Sensitivity in Earth System Models of Intermediate Complexity

Pfister, Patrik L.; Stocker, Thomas F.

doi:10.1002/2017gl075457

Cited by 18 publications

(19 citation statements)

References 38 publications

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“…Most other studies on this topic indicate a similar behavior, including a review that covers a wide range of colder and warmer climate states (von der Heydt et al, 2016). However, there have also been studies using general circulation models (GCMs) or Earth system models of intermediate complexity (EMICs) which simulate an increase in climate sensitivity for colder than present-day climate (e.g., Colman & McAvaney, 2009;Kutzbach et al, 2013;Pfister & Stocker, 2017).…”

Section: Introductionmentioning

confidence: 88%

The Effect of Obliquity‐Driven Changes on Paleoclimate Sensitivity During the Late Pleistocene

Köhler

Knorr

Stap

et al. 2018

Geophysical Research Letters

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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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Section: Introductionmentioning

confidence: 88%

The Effect of Obliquity‐Driven Changes on Paleoclimate Sensitivity During the Late Pleistocene

Köhler

Knorr

Stap

et al. 2018

Geophysical Research Letters

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“…In the two lower-ECS versions of Bern3D-LPX, the values based on year 20-150 Gregory extrapolation (circles) underestimate the true ECS slightly more than the 1000 year temperatures (diamonds), because the global feedback changes still substantially between years 150 and 1000 (Pfister 2017). The opposite is true for other EMICs where feedback changes are small (Pfister and Stocker 2017).…”

Section: Ensemble Differences and Ecs Uncertaintymentioning

confidence: 97%

“…ECS was estimated using the Gregory method experiments are available from CMIP5, which may bias the ECS estimates for statedependent ESMs (Good et al 2015, Pfister andStocker 2017). This difference in forcing magnitude may also affect the estimates of the effective radiative forcing R.…”

Section: Analysis Of Published Esm Ensemblesmentioning

confidence: 99%

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The realized warming fraction: a multi-model sensitivity study

Pfister

Stocker

2018

Environ. Res. Lett.

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The degree of physical-biogeochemical equilibration of the climate system determines for how long global warming will continue after anthropogenic CO 2 emissions have ceased. The physical part of this equilibration process is quantified by the realized warming fraction (RWF), but RWF estimates differ strongly between different climate models. Here we analyze the RWF spread and its physical causes in three model ensembles: 1. an ensemble of comprehensive climate models, 2. an ensemble of reduced-complexity models, and 3. an observationally constrained parameter ensemble of the Bern3D-LPX reduced-complexity model. We show that RWF is generally lower in models with higher equilibrium climate sensitivity. The RWF uncertainty from applying different extrapolation methods for climate sensitivity is substantial, but smaller than the inter-model spread in the three ensembles. We decompose the inter-model spread of RWF using a diagnostic global energy balance model, to compare the spread contribution by the climate sensitivity to contributions by other physical quantities: the efficiency and efficacy of ocean heat uptake, and the effective radiative forcing. In the ensembles of the comprehensive climate models and the Bern3D-LPX model, the spread of the RWF is mostly determined by the spread of the climate sensitivity; for the reduced-complexity models, the spread contribution by the ocean heat uptake efficiency is dominant. Compared to the comprehensive models, the reduced-complexity models have a lower range of climate sensitivities and lower, more unitary ocean heat uptake efficacies, resulting in higher RWF. However, by tuning such models to higher climate sensitivities, they can also achieve RWF values in the lower range of comprehensive models, as demonstrated for Bern3D-LPX. This suggests that reduced-complexity models remain useful tools for future climate change projections, but should employ a range of climate sensitivity tunings to account for the uncertainty in both the long-term warming and the RWF.

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“…Climate sensitivity characterizing the response to radiative forcing is a free parameter in BernSCM. Climate sensitivity may change under increasing warming, particularly in highemission scenarios (Geoffroy et al, 2012a;Gregory et al, 2015;Pfister and Stocker, 2017). Here, climate sensitivity is assumed to be time invariant and a potential state dependency of climate sensitivity is not considered.…”

Section: Introductionmentioning

confidence: 99%

The Bern Simple Climate Model (BernSCM) v1.0: an extensible and fully documented open-source re-implementation of the Bern reduced-form model for global carbon cycle–climate simulations

Strassmann

Joos

2018

Geosci. Model Dev.

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Abstract. The Bern Simple Climate Model (BernSCM) is a free open-source re-implementation of a reduced-form carbon cycle-climate model which has been used widely in previous scientific work and IPCC assessments. BernSCM represents the carbon cycle and climate system with a small set of equations for the heat and carbon budget, the parametrization of major nonlinearities, and the substitution of complex component systems with impulse response functions (IRFs). The IRF approach allows cost-efficient yet accurate substitution of detailed parent models of climate system components with near-linear behavior. Illustrative simulations of scenarios from previous multimodel studies show that BernSCM is broadly representative of the range of the climate-carbon cycle response simulated by more complex and detailed models. Model code (in Fortran) was written from scratch with transparency and extensibility in mind, and is provided open source. BernSCM makes scientifically sound carbon cycleclimate modeling available for many applications. Supporting up to decadal time steps with high accuracy, it is suitable for studies with high computational load and for coupling with integrated assessment models (IAMs), for example. Further applications include climate risk assessment in a business, public, or educational context and the estimation of CO 2 and climate benefits of emission mitigation options.

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State‐Dependence of the Climate Sensitivity in Earth System Models of Intermediate Complexity

Cited by 18 publications

References 38 publications

The Effect of Obliquity‐Driven Changes on Paleoclimate Sensitivity During the Late Pleistocene

The Effect of Obliquity‐Driven Changes on Paleoclimate Sensitivity During the Late Pleistocene

The realized warming fraction: a multi-model sensitivity study

The Bern Simple Climate Model (BernSCM) v1.0: an extensible and fully documented open-source re-implementation of the Bern reduced-form model for global carbon cycle–climate simulations

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