Potential for bias in effective climate sensitivity from state-dependent energetic imbalance

To estimate equilibrium climate sensitivity from a simulation where a step change in carbon dioxide concentrations is imposed, a common approach is to linearly extrapolate temperatures as a function of top-of-atmosphere energetic imbalance to estimate the equilibrium state (“effective climate sensit...

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Bibliographic Details
Published in:Earth system dynamics 2022-12, Vol.13 (4), p.1715-1736
Main Authors: Sanderson, Benjamin M, Rugenstein, Maria
Format: Article
Language:English
Subjects:
Analysis
Atmosphere
Atmospheric models
Bayesian analysis
Calibration
Carbon dioxide
Carbon dioxide concentration
Climate
Climate change
Climate models
Climate sensitivity
Environmental Sciences
Equilibrium
Experiments
Gases
Greenhouse effect
Greenhouse gases
Mathematical models
Modelling
Probability theory
Sensitivity
Simulation
Time series
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Summary:To estimate equilibrium climate sensitivity from a simulation where a step change in carbon dioxide concentrations is imposed, a common approach is to linearly extrapolate temperatures as a function of top-of-atmosphere energetic imbalance to estimate the equilibrium state (“effective climate sensitivity”). In this study, we find that this estimate may be biased in some models due to state-dependent energetic leaks. Using an ensemble of multi-millennial simulations of climate model response to a constant forcing, we estimate equilibrium climate sensitivity through Bayesian calibration of simple climate models which allow for responses from subdecadal to multi-millennial timescales. Results suggest potential biases in effective climate sensitivity in the case of particular models where radiative tendencies imply energetic imbalances which differ between pre-industrial and quadrupled CO2 states, whereas for other models even multi-thousand-year experiments are insufficient to predict the equilibrium state. These biases draw into question the utility of effective climate sensitivity as a metric of warming response to greenhouse gases and underline the requirement for operational climate sensitivity experiments on millennial timescales to better understand committed warming following a stabilization of greenhouse gases.
ISSN:2190-4987
2190-4979
2190-4987
DOI:10.5194/esd-13-1715-2022