Attribution of recent warming in Alaska

Abstract

Abstract Alaska has experienced some of the strongest warming rates in the Northern Hemisphere since the mid-20th century. The winter-season warming is especially strong: approximately 4.1\u202f°C since 1950. The atmospheric circulation contributes to interannual variability of Alaska s temperatures through advection and thereby contributes to temperature trends over decadal to multidecadal timescales. In this study, we quantify the contribution of the atmospheric circulation to Alaska s warming by using an analog methodology to identify years with sea level pressure patterns most closely resembling the pressure pattern of each year between 1950 and 2017. The analogs enable a dynamical adjustment of temperature anomalies by removing the contribution of the atmospheric circulation. The dynamical adjustment explains approximately half the variance of Alaska s statewide temperature in winter, and smaller fractions in the other seasons. The unexplained variance, termed the “excess warmth,” shows a systematic increase from 1950 to 2017. The trends in the excess warmth correspond to a warming of 2.1\u202f°C in winter and spring, 1.3\u202f°C in summer, and 0.5\u202f°C in autumn, which are consistent with the trends simulated by global climate models run with historical and projected greenhouse gas concentrations for the same period. The excess warmth accounts for 51% of the Alaska s winter warming and 75% of Alaska s annual mean warming over the 1950–2017 time period.