Climate Change in Alaska
Over the last seven decades, the linear trend for statewide mean annual temperatures is around 4.3°F. The temperature change varies from one climatic zone to another, as well as for different seasons. Below is a table of the trends in mean annual and seasonal temperatures for Alaska’s first-order observing stations since 1949, the time period for which the most reliable meteorological data are available.
Table 1. Total Change in Mean Seasonal and Annual Temperature (°F), 1949-2020.
|St. Paul Island||2.1||3.0||3.4||2.5||2.8|
Seasonal trends show that most of the change in temperatures statewide has occurred in winter and spring, with the least amount of change in summer and autumn.
Considering just a linear trend can mask some important variability characteristics in the time series. The mean annual temperature timeseries below, showing the temperature departure from the 1981-2010 climatological reference period, clearly reveals that this trend is non-linear: a linear trend might have been expected from the fairly steady observed increase of CO2 during this time period. However, there are large variations from year to year.
The stepwise shift appearing in the temperature data in 1976 corresponds to a phase shift of the Pacific Decadal Oscillation from a negative phase to a positive phase. Synoptic conditions with the positive phase tend to consist of increased southerly flow and warm air advection into Alaska during the winter, resulting in positive temperature anomalies.
Table 2. Total Change in Mean Seasonal and Annual Temperature (°F), 1976-2020.
|St. Paul Island||-0.2||2.4||2.3||3.6||2.5|
The change in temperature over time influences our concept of what temperatures are considered “normal”. When we refer to temperatures being warmer or colder than normal, we are comparing the current conditions to averages over a 30-year climatological reference period. Every ten years, the reference period changes and the climate normals are recalculated. On May 4, 2021, the National Oceanic and Atmospheric Administration (NOAA) released the U.S. Climate Normals dataset for the 1991-2020 reference period. To examine the difference in annual and seasonal temperatures between the new reference period and the previous reference period (1981-2010), below are anomaly maps using temperature values from the ECMWF ERA5 Reanalysis.
Annual (top) and seasonal anomaly maps of normal temperatures (1991 – 2020 normal minus 1981 – 2010 normal), as derived from the ECMWF ERA5 reanalysis dataset (data source: Climate Reanalyzer, Climate Change Institute, University of Maine).
With the long-term temperature trend, the new temperature normal show that the state is warming. Annual average temperatures for the 1991-2020 normal period have increased 1-3°F across the state compared to the 1981-2010 normals. The most significant temperature increases have occurred along the North Slope, the Arctic Coast, and the adjacent Arctic Ocean from the Beaufort to the Chukchi Sea. This is due to the replacement of the cooler 1980s with the much warmer 2010s in the calculation of the normal. Average temperatures in the 2010s increased the most in autumn due to increased sea ice loss and historically low minimum sea ice extent. The change in temperature normals will mean that hotter temperatures will tend to not be as extreme while cold temperatures may seem to be more extreme.