Abstract/Summary

We show that the wintertime (December‐January‐February) North Pacific jet in ERA5 has shiftednorthwards over the satellite‐era (1979–2023) at a faster rate than any of the state‐of‐the‐art coupled climatemodels used in this study. Differences in tropical sea surface temperature (SST) trends can only partially explainthe discrepancy in jet trends between models and observations and a small minority of simulations forced withobserved SSTs match the magnitude of the observed jet trend. However, analysis of longer‐term jet variability inreanalysis 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 differingresponses to anthropogenic forcing or overly weak long‐term internal variability in models. These results haveimportant implications for future climate projections for North America and motivate further research into theunderlying causes of long‐term jet trends.