<p>Climate warming accelerated as the Atlantic Multidecadal Oscillation (AMO) transitioned from negative to positive phase, facilitating clearer climatological detection. Notably, atmospheric circulation patterns observed in the extratropical Northern Hemisphere during the AMO’s transition to the end of the twentieth century differed from those observed in earlier periods, indicating an altered influence of AMO-related mechanisms. During the 1915–1944 transition, the East Asian westerly jet stream moved northward and was associated with greater tropical convective activity across the Maritime Continent. The corresponding poleward extension of the Hadley circulation was dynamically linked to strengthened ground-level winter monsoon flow near the surface across East Asia, bordered by the intensified Siberian high and Aleutian low. A globally uniform circulation change that manifested as a belt across the lower latitudes was clearly distinguishable. Although tropical convective activity increased during the 1985–2014 transition, the northward-shifting midlatitude jet stream experienced considerable disruption, which coincided with more frequent seasonal blocking and severe weather events. The response of upper tropospheric circulation to warming varied locally rather than uniformly across the globe. Concerns were raised about the usefulness of AMO periodicity for tracking time-varying climatological conditions, whether or not they are related to varied levels of warming. The transformation in hemispheric resonance also questioned the uncertainty of climate variability in climate modeling, raising concerns about the reliability of some climate change estimates.</p> Graphical Abstract <p></p> <p>From the 1910s to the 1940s, rapid climatological warming (lower panel) was correlated with a northward shift of the midlatitude westerly jet stream in the upper troposphere and a poleward expansion of the Hadley circulation. Over East Asia, this expansion was associated with enhanced winter surface monsoon flow, which was flanked by a reinforced Siberian high and Aleutian low, and increased tropical convective activity to the south across the Maritime Continent. This globally uniform change in circulation, manifesting as a belt-like pattern at lower latitudes (as the 300-hPa stream-functions shown in the upper panels), may be readily understood to be typical of an AMO-scale change (transitioned from negative to positive phase). However, in response to rapid warming in the late twentieth century (from the 1980s to the 2010s), large changes around the Arctic likely disrupted the extratropical westerly jet stream as it propagated north. Atmospheric circulation patterns in the extratropical Northern Hemisphere observed during the transition varied differently when compared with those observed during earlier periods; this led to intensified seasonal blocking and severe weather conditions, which are indicative of altered AMO-related mechanisms. Notably, the transformation in hemispheric resonance was only partially detected in climate models. Researchers have also raised concerns about the practicality of using periodicity as a basis for tracking the evolution of climatological conditions and about uncertainty in change forecasts.</p>