Atmosphere Assessments

2015 Arctic Atmosphere Temperature

Aaron Letterly

Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin, Madison, WI, USA

10 September 2016

Mean Annual Surface Air Temperature

From October 2014 - September 2015, the average annual surface temperature anomaly, based on the 1981-2010 mean, was +1.3°C over land poleward of 60°N. This air temperature anomaly was driven by positive temperature anomalies in all seasons over the previous year, particularly in the Alaskan and Siberian Arctic from October to June. In these regions, three-month anomalies were consistently +3°C or greater. Temperature anomalies over the ocean spanning from the Kara Sea to the Fram Strait were positive to neutral the entire year. Based on three-month averages, the central Arctic temperature anomaly stayed at or above +1°C year-round. The October 2014 - September 2015 observation period exhibited the largest positive temperature anomaly over land 60°N and poleward since the beginning of the observational record in 1900.

Polar temperature anomalies in 2015 were far more positive than temperature anomalies in the mid-latitudes, and can be seen in Figure 1. More extreme anomalies in the polar region are representative of Arctic amplification - which refers to more dramatic manifestations of warming or cooling at the poles compared to the mid-latitudes. The temperature increases over the Arctic in the 21st century are more than twice the 1.5° C increase observed over the entire Northern Hemisphere, shown in Figure 2 (Overland et al., 2011; Stroeve et al., 2012). The black line in Figure 2 shows that temperature anomalies over land 60° N (black line) or higher were far more intense than mid-latitude anomalies that same year (red and blue bars). Since 1990, Northern Hemisphere temperatures have been consistently warmer than the 1981-2010 baseline. Figure 3 shows that the most recent five-year period over the Arctic Ocean was much warmer than the 1981-2010 climatological baseline.

Seasonal Air Temperature

Fall and winter 2015 experienced a neutral NAO pattern along with a generally weak pressure gradient between the American and Siberian Arctic, resulting in an unremarkable Arctic Dipole. Circulation in the winter was largely influenced by strong low pressure zones throughout the Central Arctic and over Alaska (Figure 5). Winds follow the contours of pressure counterclockwise around low-pressure zones, resulting in the strong southern winds reinforcing high temperatures off of the Siberian Arctic as well as blowing the Beaufort Sea ice away from the northern Alaskan coastline in the winter of 2015.

Severe Weather

For all but the last few days of 2015, the Arctic was relatively unaffected by extreme weather events. An intense low pressure system near Iceland and weaker low pressure system over the North pole, coupled with a strong high pressure system over central Europe formed a steep pressure gradient on December 30, 2015. The extreme difference in pressures created a dramatic inflow of warm air to the North Pole area as the low pressure system over Iceland strengthened to 935 hPa. A buoy weather station near the North Pole momentarily recorded temperatures of +0.7° C, possibly exceeding the freezing point and 23° C above average temperatures in that region. The intrusion of warm air was so short lived, however, it is unlikely that its effects reached much further than a week of slower local ice growth in early January.

References

Overland, J. E., J. A. Francis, E. Hanna and M. Wang. 2012. The recent shift in early summer arctic atmospheric circulation. Geophys. Res. Lett., doi: 10.1029/2012GL053268.

Stroeve, J. C., M. C. Serreze, M. M. Holland, J. E. Kay, J. Maslanik and A. P. Barrett. 2012. The Arctic's rapidly shrinking sea ice cover: a research synthesis. Climatic Change, doi 10.1007/s10584-011-0101-1.