The significance of the 1976 Pacific climate shift in the climatology of Alaska

The 1976 Pacific climate shift is examined, and its manifestations and significance in Alaskan climatology during the last half-century are demonstrated. The Pacific Decadal Oscillation index shifted in 1976 from dominantly negative values for the 25-yr time period 1951-75 to dominantly positive values for the period 1977-2001. Mean annual and seasonal temperatures for the positive phase were up to 3.1 degrees C higher than for the negative phase. Likewise, mean cloudiness, wind speeds, and precipitation amounts increased, while mean sea level pressure and geopotential heights decreased. The pressure decrease resulted in a deepening of the Aleutian low in winter and spring. The intensification of the Aleutian low increased the advection of relatively warm and moist air to Alaska and storminess over the state during winter and spring. The regime shift is also examined for its effect on the long-term temperature trends throughout the state. The trends that have shown climatic warming are strongly biased by the sudden shift in 1976 from the cooler regime to a warmer regime. When analyzing the total time period from 1951 to 2001, warming is observed; however, the 25-yr period trend analyses before 1976 (1951-75) and thereafter (1977-2001) both display cooling, with a few exceptions. In this paper, emphasis is placed on the importance of taking into account the sudden changes that result from abrupt climatic shifts, persistent regimes, and the possibility of cyclic oscillations, such as the PDO, in the analysis of long-term climate change in Alaska.