Brief communication: Reanalyses underperform in cold regions, raising concerns for climate services and research

Many changes in cold regions are amplified by nonlinear processes involving ice and have important consequences locally and globally. We show that the average ensemble spread of the mean annual air temperature (1.5 °C) in the reanalyses is 90 % greater in cold regions compared to the other regions and shows pronounced disagreement in the trend. The ensemble spread in the mean annual maximum snow water equivalent is found to be greater than the ensemble mean. The reduced quality of reanalyses in cold regions, coinciding with sparse in situ observations and low population, points to challenges in how we represent cold-region phenomena in simulation systems and limits our ability to support climate research and services.