Coexchangeable process modelling for uncertainty quantification in joint climate reconstruction

Abstract

Any experiment with climate models relies on a potentially large set of spatiotemporal boundary conditions. These can represent both the initial state of the system and/or forcings driving the model output throughout the experiment. Whilst these boundary conditions are typically fixed using available reconstructions in climate modelling studies, they are highly uncertain, that uncertainty is unquantified, and the effect on the output of the experiment can be considerable. We develop efficient quantification of these uncertainties that combines relevant data from multiple models and observations. Starting from the coexchangeability model, we develop a coexchangable process model to capture multiple correlated spatio-temporal fields of variables. We demonstrate that further exchangeability judgements over the parameters within this representation lead to a Bayes linear analogy of a hierarchical model. We use the framework to provide a joint reconstruction of sea-surface temperature and sea-ice concentration boundary conditions at the last glacial maximum (19-23 ka) and use it to force an ensemble of ice-sheet simulations using the FAMOUS-Ice coupled atmosphere and ice-sheet model. We demonstrate that existing boundary conditions typically used in these experiments are implausible given our uncertainties and demonstrate the impact of using more plausible boundary conditions on ice-sheet simulation.

De‐Tuning Albedo Parameters in a Coupled Climate Ice Sheet Model to Simulate the North American Ice Sheet at the Last Glacial Maximum

“…SSTs and SICs are taken from the statistical reconstruction of Astfalck et al (2021), combining information from the PMIP LGM multi-model ensemble (Kageyama et al, 2021b) and compilations of proxy data (Kucera et al, 2005), and their associated uncertainties. The method is able to generate ensembles of plausible SST and SIC pairs that can be used to drive atmosphere models.…”

De-tuning a coupled Climate Ice Sheet Model to simulate the North American Ice Sheet at the Last Glacial Maximum

“…SSTs and sea ice concentrations are taken from the statistical reconstruction of Astfalck et al (2021), combining information from the PMIP LGM multi-model ensemble (Kageyama, Harrison, et al, 2021) and compilations of proxy data (Kucera et al, 2005), and their associated uncertainties. The method is able to generate ensembles of plausible SST and SIC pairs that can be used to drive atmosphere models.…”