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Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

Impact:
We have shown that a concurrent phase shift of Pacific decadal variability (PDV) and Atlantic multidecadal variability (AMV) modes is a major mechanism for the unusually intense early 20th-century Arctic warming, and that the atmospheric circulation change is important. Our atmospheric general circulation model (AGCM) experiments indicate constructive contributions of the tropical and extratropical sea surface temperature (SST) forcings. The tropical Pacific warming excites a Pacific/North America (PNA)-like circulation change while the extratropical SST warming strengthens meridional sea level pressure (SLP) gradient over northern Eurasia. The North Atlantic plays a key role in changing atmospheric circulation over the Eurasian Arctic. The Pacific/Atlantic SST warming in the early 20th century was underrepresented in previous reconstructed SST datasets. Our AGCM successfully reproduces the magnitude and spatial distribution of the early Arctic warming when the phase shift of PDV/AMV modes is properly represented. Long coupled model simulations confirm that concurrent PDV–AMV phase shifts affect Arctic temperature trends (Fig. 5), highlighting the importance of regional patterns of SST change. The sensitivity to SST also highlights the need for the reliable reconstruction of the historical evolution, especially before 1950.

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