Use of Shallow Ice Core Measurements to Evaluate and Constrain 1980–1990 Global Reanalyses of Ice Sheet Precipitation Rates

Sea‐level rise (SLR) projections by Earth System Models (ESMs) depend on ice sheet surface mass balances. Accurate, global atmosphere reanalyses would be ideal for providing equilibrated ice sheet model initial conditions in fully coupled ESM simulations. Here we present the first evaluation of 1980–1990 global reanalysis precipitation over Greenland and Antarctica that uses independent observations of net accumulation rates derived from shallow ice cores. Precipitation distributions from both the European Centre for Medium‐Range Weather Forecast's Reanalysis (ERA5) and the Modern‐Era Retrospective Analysis for Research and Applications (MERRA‐2) are highly correlated with contemporaneous co‐located net accumulation rates from Greenland (r2 > 0.95) and West Antarctica (r2 > 0.7). Three other commonly used reanalyses (WFDE5, CRUNCEP, and GSWP3) exhibit significantly weaker correlations on one or both ice sheets. Our findings imply that ESMs should use ERA5 or MERRA‐2 in data‐forced simulations to validate ice sheet model dynamics and precondition firn for SLR projections. Plain Language Summary Because they assimilate observational data into self‐consistent models, atmospheric reanalyses are generally considered the best products for estimating the historical evolution of Earth's atmosphere. For this reason, their surface fields commonly provide land surface models with input data to study the impacts of climate change. To determine which reanalysis data set provides the best input data over Greenland and Antarctica, we compare precipitation from five reanalysis data sets to ice core measurements. We find that two reanalysis data sets provide accurate long‐term precipitation fields over Greenland, indicating their utility for ice sheet studies. Overall, we suggest the application of specific reanalysis data sets to improve future studies of sea‐level rise from ice sheets. Key Points Net accumulation measured in shallow ice cores, adjusted for sublimation/deposition, constrains climatological precipitation over ice sheets ERA5 and MERRA‐2 precipitation fields over Greenland are highly correlated (r2 > 0.95) with in situ measurements of net accumulation Other widely used reanalyses (WFDE5, CRUNCEP, and GSWP3) are unfit for studies of ice sheet surface mass balance