Is the Last Interglacial Warm Period a Good Analog for Future Greenland Mass Balance?

The substantial deglaciation of the Greenland Ice Sheet (GrIS) in the Last Interglacial warm period (LIG, 127,000 years ago) is often referred to as an “imperfect analog” for Greenland sensitivity and melt under anthropogenic climate change. Understanding the LIG GrIS deglaciation helps quantify its contribution to sea level rise, offering insights into future projections. However, the LIG warmth was due to high boreal summer insolation controlled by Earth’s orbital configuration, whereas the observed anthropogenic warming is primarily attributed to elevated concentrations of atmospheric greenhouse gasses. To this end, we investigate the GrIS and the North Atlantic response to insolation versus greenhouse gas concentrations in simulations from the Community Earth System Model, version 2 (CESM2). The model simulations suggest that the difference in spatial signature of GrIS surface mass balance is controlled by local precipitation. In the future high CO₂ world, the GrIS is expected to melt faster in the South and slower in the North compared to the LIG. This difference is due to reduced winter precipitation over southern Greenland in the future world, as well as a stronger seasonal cycle in the LIG. In the future high CO₂ world, reduced winter precipitation over the GrIS is tied to an equatorward shift in extratropical storm trajectories, as well as a regional cold anomaly in the North Atlantic that is related to a weakening of the meridional overturning circulation. In the LIG world, precipitation seasonality is stronger and the North Atlantic jet stream and storm track are shifted equatorward due to increased cyclonic breaking of Rossby waves in winter months. The differences in climate responses between the LIG and future scenarios indicate that direct comparisons may oversimplify the many mechanisms involved. As such, caution is potentially warranted when using the LIG as an analog for anthropogenic change, particularly in the context of 21st century sea level rise.