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Earth System Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Sep 2018

Research article | 27 Sep 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth System Dynamics (ESD).

Evaluating Climate Emulation: Unit Testing of Simple Climate Models

Adria K. Schwarber1, Steven J. Smith1,2, Corinne A. Hartin2, Benjamin Aaron Vega-Westhoff3, and Ryan Sriver3 Adria K. Schwarber et al.
  • 1Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742
  • 2Joint Global Change Research Institute, 5825 University Research Ct, College Park, MD 20740
  • 3Department of Atmospheric Sciences, University of Illinois Urbana-Champaign, Champaign, IL 61820

Abstract. Simple climate models (SCMs) are numerical representations of the Earth’s gas cycles and climate system. SCMs are easy to use and computationally inexpensive, making them an ideal tool in both scientific and decision-making contexts (e.g., complex climate model emulation; parameter estimation experiments; climate metric calculations; and probabilistic analyses). Despite their prolific use, the fundamental responses of SCMs are often not directly characterized. In this study, we use unit tests of three chemical species (CO2, CH4, and BC) to understand the fundamental gas cycle and climate system responses of several SCMs (Hector v2.0, MAGICC 5.3, MAGICC 6.0, FAIR v1.0, and AR5-IR). We find that while idealized SCMs are widely used, they fail to capture important global mean climate response features, which can produce biased temperature results. Comprehensive SCMs, which have non-linear forcing and physically-based carbon cycle representations, show improved responses compared to idealized SCMs. Even some comprehensive SCMs fail to capture response timescales of more complex models under BC or CO2 forcing perturbations. These results suggest where improvements should be made to SCMs. Further, we provide a set of fundamental tests that we recommend as a standard validation suite for any SCM. Unit tests allow users to understand differences in model responses and the impact of model selection on results.

Adria K. Schwarber et al.
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Adria K. Schwarber et al.
Adria K. Schwarber et al.
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Publications Copernicus
Short summary
Simple climate models (SCMs) underlie many important scientific and decision-making endeavors. This illustrates the need for their use to be rooted in a clear understanding of their fundamental responses. In this study, we provide a comprehensive assessment of model performance by evaluating the fundamental responses of several SCMs. We find biases in some responses, which have implication for decision science. We conclude by recommending a standard set of validation test for any SCM.
Simple climate models (SCMs) underlie many important scientific and decision-making endeavors....