Abstract
Abstract. We describe the creation of a data set describing changes related to the presence of ice sheets, including ice-sheet extent and height, ice-shelf extent, and the distribution and elevation of ice-free land at the Last Glacial Maximum (LGM), which were used in LGM experiments conducted as part of the fifth phase of the Coupled Modelling Intercomparison Project (CMIP5) and the third phase of the Palaeoclimate Modelling Intercomparison Project (PMIP3). The CMIP5/PMIP3 data sets were created from reconstructions made by three different groups, which were all obtained using a model-inversion approach but differ in the assumptions used in the modelling and in the type of data used as constraints. The ice-sheet extent in the Northern Hemisphere (NH) does not vary substantially between the three individual data sources. The difference in the topography of the NH ice sheets is also moderate, and smaller than the differences between these reconstructions (and the resultant composite reconstruction) and ice-sheet reconstructions used in previous generations of PMIP. Only two of the individual reconstructions provide information for Antarctica. The discrepancy between these two reconstructions is larger than the difference for the NH ice sheets, although still less than the difference between the composite reconstruction and previous PMIP ice-sheet reconstructions. Although largely confined to the ice-covered regions, differences between the climate response to the individual LGM reconstructions extend over the North Atlantic Ocean and Northern Hemisphere continents, partly through atmospheric stationary waves. Differences between the climate response to the CMIP5/PMIP3 composite and any individual ice-sheet reconstruction are smaller than those between the CMIP5/PMIP3 composite and the ice sheet used in the last phase of PMIP (PMIP2).
Highlights
There are large differences in the modelled response to scenarios of future climate forcing (Kirtman et al, 2013; Collins et al, 2013)
We describe the creation of a data set describing changes related to the presence of ice sheets, including ice-sheet extent and height, ice-shelf extent, and the distribution and elevation of ice-free land at the Last Glacial Maximum (LGM), which were used in LGM experiments conducted as part of the fifth phase of the Coupled Modelling Intercomparison Project (CMIP5) and the third phase of the Palaeoclimate Modelling Intercomparison Project (PMIP3)
ICE-6G is the latest of a series of inversions of a glacial isostatic adjustment (GIA) model based on the solution for the impulse response of a viscoelastic Earth to surface loading described by Peltier (1974), in which global ice history and radial Earth viscosity profiles are repeatedly tuned to improve model predictions of relative sea-level (RSL) histories and present-day deformation rates compared to observations (Peltier and Andrews, 1976; Tushingham and Peltier, 1991; Peltier, 1976, 1994, 2002, 2004; Argus and Peltier, 2010; Engelhart et al, 2011)
Summary
There are large differences in the modelled response to scenarios of future climate forcing (Kirtman et al, 2013; Collins et al, 2013). A. Abe-Ouchi et al.: PMIP3 ice-sheet configuration to large changes in forcing (Braconnot et al, 2012; MassonDelmotte et al, 2013; Schmidt et al, 2014; Harrison et al, 2015). The boundary conditions that must be specified for the LGM experiment are a (relatively small) change in orbital forcing, reduced atmospheric concentrations of greenhouse gases, and the presence of large ice sheets. The differences between this blended ice sheet, the individual ice-sheet reconstructions, and previous ice-sheet configurations used by PMIP, and their impact on forcing and climate, are discussed in Sect. It makes recommendations for further work to investigate the impact of ice-sheet configuration on climate change as well as to minimise these uncertainties
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