Pacific contribution to the early twentieth-century warming in the Arctic

摘要

Arctic surface temperature warmed more than twice as fast as global temperature during the early twentieth century, similar to that during the recent global warming. This Arcticwarming has been attributed to both external forcing and i internal variability associated with atmospheric dynamics and Atlantic Ocean temperature in combination with Pacificvariability. Here we show, through coupled climate model experiments that superpose externally forced and dynami- cally driven changes, that Pacific decadal variability alonewas a key contributor to the early twentieth century Arcticwarming. Sea surface temperatures in the model are phasedto observations by prescribing historical wind variations overthe Pacific, which drive thermodynamically consistent decadalvariations. During the early twentieth century, the PacificDecadal Oscillation (PDO) transitioned to a positive phasewith a concomitant deepening of the Aleutian Low that warmsthe Arctic by poleward low-level advection of extratropical air.In addition, our experiments revealed that the implementedPacific surface changes weaken the polar vortex, which leadsto subsidence-induced adiabatic heating of the Arctic surface,Thus, our results suggest that the observed recent shift to thepositive PDO phase6 will intensify Arctic warming in the forth-coming decades.