Evidence
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A central challenge in this context is that the inferred value of ECS can depend on the statistical model used to represent structural discrepancies between the reduced energy balance model and the full ESM output.
Passages supplied to the Evidence version
Card 1 · Dependence of Inferred Climate Sensitivity on the Discrepancy Model
We consider the effect of different temporal error structures on the inference of equilibrium climate sensitivity 1 1 1 ECS is defined as the realized equilibrium surface warming—globally-averaged surface air temperature—for a doubling of CO 2 (ECS), in the context of an energy balance model (EBM) t…
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We consider the effect of different temporal error structures on the inference of equilibrium climate sensitivity 1 1 1 ECS is defined as the realized equilibrium surface warming—globally-averaged surface air temperature—for a doubling of CO 2 (ECS), in the context of an energy balance model (EBM) that is commonly employed in analyzing earth system models (ESM) and observations. We consider error structures ranging from uncorrelated (IID normal) to AR(1) to Gaussian correlation (Gaussian Process GP) to analyze the abrupt 4xCO 2 CMIP5 experiment in twenty-one different ESMs. For seven of the ESMs, the posterior distribution of ECS is seen to depend rather weakly on the discrepancy model used suggesting that the discrepancies were largely uncorrelated.
Card 2 · Climate response and sensitivity: time scales and late tipping points
Climate response metrics are used to quantify the Earth’s climate response to anthropogenic changes of atmospheric CO 2 . Equilibrium climate sensitivity (ECS) is one such metric that measures the equilibrium response to CO 2 doubling. However, both in their estimation and their usage, such metrics…
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Climate response metrics are used to quantify the Earth’s climate response to anthropogenic changes of atmospheric CO 2 . Equilibrium climate sensitivity (ECS) is one such metric that measures the equilibrium response to CO 2 doubling. However, both in their estimation and their usage, such metrics make assumptions on the linearity of climate response, although it is known that, especially for larger forcing levels, response can be nonlinear. Such nonlinear responses may become visible immediately in response to a larger perturbation, or may only become apparent after a long transient period. In this paper, we illustrate some potential problems and caveats when estimating ECS from transient simulations. We highlight ways that very slow time scales may lead to poor estimation of ECS even if there is seemingly good fit to linear response over moderate time scales. Moreover, such slow processes might lead to late abrupt responses (late tipping points) associated with a system’s nonlineari …
Card 3 · Extreme Sensitivity and Climate Tipping Points
Abstract A climate state close to a tipping point will have a degenerate linear response to perturbations, which can be associated with extreme values of the equilibrium climate sensitivity (ECS). In this paper we contrast linearized (‘instantaneous’) with fully nonlinear geometric (‘two-point’) not…
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Abstract A climate state close to a tipping point will have a degenerate linear response to perturbations, which can be associated with extreme values of the equilibrium climate sensitivity (ECS). In this paper we contrast linearized (‘instantaneous’) with fully nonlinear geometric (‘two-point’) notions of ECS, in both presence and absence of tipping points. For a stochastic energy balance model of the global mean surface temperature with two stable regimes, we confirm that tipping events cause the appearance of extremes in both notions of ECS. Moreover, multiple regimes with different mean sensitivities are visible in the two-point ECS. We confirm some of our findings in a physics-based multi-box model of the climate system.
Card 4 · Beyond Forcing Scenarios: Predicting Climate Change through Response Operators in a Coupled General Circulation Model
Abstract Global Climate Models are key tools for predicting the future response of the climate system to a variety of natural and anthropogenic forcings. Here we show how to use statistical mechanics to construct operators able to flexibly predict climate change. We perform our study using a fully c…
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Abstract Global Climate Models are key tools for predicting the future response of the climate system to a variety of natural and anthropogenic forcings. Here we show how to use statistical mechanics to construct operators able to flexibly predict climate change. We perform our study using a fully coupled model - MPI-ESM v.1.2 - and for the first time we prove the effectiveness of response theory in predicting future climate response to CO2 increase on a vast range of temporal scales, from inter-annual to centennial, and for very diverse climatic variables. We investigate within a unified perspective the transient climate response and the equilibrium climate sensitivity, and assess the role of fast and slow processes. The prediction of the ocean heat uptake highlights the very slow relaxation to a newly established steady state. The change in the Atlantic Meridional Overturning Circulation (AMOC) and of the Antarctic Circumpolar Current (ACC) is accurately predicted. The AMOC strength …
Card 5 · Dependence of Inferred Climate Sensitivity on the Discrepancy Model
We consider the effect of different temporal error structures on the inference of equilibrium climate sensitivity 1 1 1 ECS is defined as the realized equilibrium surface warming—globally-averaged surface air temperature—for a doubling of CO 2 (ECS), in the context of an energy balance model (EBM) t…
Read full passage excerpt
We consider the effect of different temporal error structures on the inference of equilibrium climate sensitivity 1 1 1 ECS is defined as the realized equilibrium surface warming—globally-averaged surface air temperature—for a doubling of CO 2 (ECS), in the context of an energy balance model (EBM) that is commonly employed in analyzing earth system models (ESM) and observations. We consider error structures ranging from uncorrelated (IID normal) to AR(1) to Gaussian correlation (Gaussian Process GP) to analyze the abrupt 4xCO 2 CMIP5 experiment in twenty-one different ESMs. For seven of the ESMs, the posterior distribution of ECS is seen to depend rather weakly on the discrepancy model used suggesting that the discrepancies were largely uncorrelated.
Model-reported card use
Card 1 · fact
Affected output: the inferred value of ECS can depend on the statistical model used to represent structural discrepancies between the reduced energy balance model and the full ESM output
Model explanation: This row supplies the concrete fact that ECS inference from an energy balance model depends on the discrepancy model, which is the substantive content of the new paragraph.
Card 2 · terminology
Affected output: structural discrepancies
Model explanation: This row's framing of assumptions underlying ECS estimation informed the use of 'structural discrepancies' to describe the gap between reduced and full models.