Abstract The large‐scale atmospheric circulation plays an important role in regional climate. Recent studies have shown that poleward shifts in the Northern Hemisphere jet streams may be emerging, but the statistical significance and robustness are questionable. Here we show that a human fingerprint in the zonal mean, zonal winds has emerged above background internal variability in observed trends during boreal winter. The observed signal is highly statistically significant over 1980–2023 and robust across different reanalyses. The model fingerprint consists of a tripole pattern with strengthening of the westerly winds in the midlatitudes and weakening at both lower and higher latitudes. Single forcing simulations reveal that these trends are attributed to anthropogenic greenhouse gases increases. The magnitude of the observed signal is outside the range simulated by seven large ensemble simulations, suggesting that models underestimate either the anthropogenic forced signal, the magnitude of internal variability on multidecadal timescales, or both.
Blackport et al. (Mon,) studied this question.