Attribution of recent warming in Alaska Polar Science

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 °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 °C in winter and spring, 1.3 °C in summer, and 0.5 °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. Grant no. NA15OAR4310169 Grant no. NA16OAR4310162