Climate Models Struggle to Simulate Observed North Pacific Jet Trends, Even Accounting for Tropical Pacific Sea Surface Temperature Trends

Abstract

We show that the wintertime (December-January-February) North Pacific jet in ERA5 has shifted northwards over the satellite-era (1979–2023) at a faster rate than any of the state-of-the-art coupled climate models used in this study. Differences in tropical sea surface temperature (SST) trends can only partially explain the discrepancy in jet trends between models and observations and a small minority of simulations forced with observed SSTs match the magnitude of the observed jet trend. However, analysis of longer-term jet variability in reanalysis suggests that the jet trend has not clearly emerged from multi-decadal internal climate variability. Consequently, it is unclear whether the difference in observed and modeled jet trends arises due to differing responses to anthropogenic forcing or overly weak long-term internal variability in models. These results have important implications for future climate projections for North America and motivate further research into the underlying causes of long-term jet trends.