Global Glacial Inception Areas during the Last Glacial Maximum

Despite extensive research on Last Glacial Maximum (LGM) glaciers, the complexity of the record means that data are often fragmented and regionally focused, limiting the availability of cohesive global field-based reconstructions and models. Developing methods to work globally is necessary to uncover undocumented glaciations and gain a better understanding of the extent of past glacial systems. In this study we used a 30 arcsecond, degree-day based glacial inception threshold map, estimating the temperature reductions required for glaciation relative to the current climate. By integrating results from eleven PMIP4 (Paleoclimate Modelling Intercomparison Project Phase 4) simulations, we identified areas where temperatures dropped sufficiently during the LGM to support glaciation in each model, and aggregated them into a global map of the number of PMIP4 models predicting conditions for glacial inception. To validate these findings, we used a dataset of ¹⁰Be and ²⁶Al radionuclide dates from glacial landforms. Using these dated points as outlet locations, we delineated watershed basins approximating potential glacier extents. The resulting polygons were merged with a vector map of documented glacial extents and then spatially compared to the modelled inception areas. Initial results indicated that only 25.99% of the documented LGM glaciers align with the aggregated inception areas as modelled by the majority of PMIP4 models, while 74.01% remain unreproduced, likely due to paleoclimate modelling resolution and spatial mismatches between inception areas and outlet points. Conversely, 49.19% of the inception areas lacked corresponding documentation, suggesting the potential existence of previously unreported glaciers. When considering regions where at least one PMIP4 model predicts threshold temperatures, 67.01% do not correspond with known paleoglaciers. Areas where all models agree on suitable conditions for glaciation, coincide with only 6.06% of documented glaciers. Future research could refine these methods by incorporating higher-resolution palaeoclimate model outputs and using ice flow modelling to delineate glacier extents more accurately.