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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Methods for assessment of models 14 Feb 2018

Methods for assessment of models | 14 Feb 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Geoscientific Model Development (GMD).

ATAT 1.0, an Automated Timing Accordance Tool for comparing ice-sheet model output with geochronological data

Jeremy C. Ely1, Chris D. Clark1, David Small2, and Richard C. A. Hindmarsh3 Jeremy C. Ely et al.
  • 1Department of Geography, The University of Sheffield, Sheffield, S10 2TN, UK
  • 2Department of Geography, Durham University, Durham, DH1 3LE, UK
  • 3British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK

Abstract. Earth's extant ice sheets are of great societal importance given their ongoing and potential future contributions to sea-level rise. Numerical models of ice sheets are designed to simulate ice sheet behaviour in response to climate changes, but to be improved require validation against observations. The direct observational record of extant ice sheets is limited to a few recent decades, but there is a large and growing body of geochronological evidence spanning millennia constraining the behaviour of palaeo-ice sheets. Hindcasts can be used to improve model formulations and study interactions between ice sheets, the climate system and landscape. However, ice-sheet modelling results have inherent quantitative errors stemming from parameter uncertainty and their internal dynamics, leading many modellers to perform ensemble simulations, while uncertainty in geochronological evidence necessitates expert interpretation. Quantitative tools are essential to examine which members of an ice-sheet model ensemble best fit the constraints provided by geochronological data. We present an Automated Timing Accordance Tool (ATAT version 1.0) used to quantify differences between model results and geo-data on the timing of ice sheet advance and/or retreat. To demonstrate its utility, we perform three simplified ice-sheet modelling experiments of the former British-Irish Ice Sheet. These illustrate how ATAT can be used to quantify model performance, either by using the discrete locations where the data originated together with dating constraints or by comparing model outputs with empirically-derived reconstructions that have used these data along with wider expert knowledge. The ATAT code is made available and can be used by ice-sheet modellers to quantify the goodness of fit of hindcasts. ATAT may also be useful for highlighting data inconsistent with glaciological principles or reconstructions that cannot be replicated by an ice sheet model.

Jeremy C. Ely et al.
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Jeremy C. Ely et al.
Model code and software

ATAT v 1.0 J. C. Ely, C. D. Clark, D. Small, and R. C. A. Hindmarsh

Jeremy C. Ely et al.
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Latest update: 18 Oct 2018
Publications Copernicus
Short summary
During the last 2.6 million years, the Earth's climate has cycled between cold glacials and warm interglacials, causing the growth and retreat of ice-sheets. These ice sheets can be independently reconstructed using numerical models or from dated evidence that they leave behind (e.g. sediments, boulders). We here present a tool for comparing numerical model simulations with dated ice sheet material. We demonstrate the utility of this tool by applying it to the last British-Irish ice-sheet.
During the last 2.6 million years, the Earth's climate has cycled between cold glacials and warm...