Glacier ice loss in Central-Western Greenland from last-millennium maximum to present

The melting of snow and ice in Greenland has accelerated since the 1990s, resulting in significant impacts on the ecosystem, such as sea-level rise. However, the spatiotemporal evolution of Greenland's peripheral glaciers and ice caps (GICs) during the late Holocene period remains poorly understood. Understanding the maximum extent of these glaciers during the last millennium contextualize ongoing glacier trends in response to a changing climate. Currently, there is a lack of agreement between geological evidence of last-millennium maximum moraine extension and the prevailing climate conditions of that time. In this study, we aimed to model the past evolution of GICs in Central-Western Greenland and estimate anomalies relative to present-day conditions to reconcile past climate and quantify committed ice loss within a changing climate. We utilized the Instructed Glacier Model (IGM), a physically based glacier model incorporating mass conservation principles and deep learning emulator to estimate 3D ice-flow dynamics. Initially, the IGM was calibrated and validated using an ensemble of model parameterization options and climate perturbed conditions to reproduce the actual glacier area and ice thickness. The model successfully replicated ice-thickness and glaciers extension, reaching stable-state conditions for glacier area after a 500-year model run. This validated model was then forced with a range of potential air temperature and precipitation conditions based on estimates derived from ice core data near the study area. The resulting maximum glacier termini were validated with cosmogenic dating evidence from the last millennium (late Medieval Warm Period and onset of the Little Ice Age). The results indicated that air temperatures were at least < -0.75 ºC compared to the baseline climate (1960-1990 period) or <-0.5ºC with precipitation > 10%. These calibrated climate conditions suggested a reduction in glacier area and an ice thickness of approximately 20% compared to near present-day (2022) conditions. Using positive degree-day function calibrated with mass balance data, and a long-term model run (500 years after calibration), an increase of +1ºC would lead to a decrease in glacier area and ice thickness of around >50% compared to present-day conditions. These findings provide insights into the past glacier evolution within a long-term temporal perspective and help contextualize ongoing glacier retreat in response to climate change.