J. Overland1, E. Hanna2 , I. Hanssen-Bauer3, B.-M. Kim4, S.-J. Kim4, J. Walsh5, M. Wang6, U. Bhatt7
1NOAA/PMEL, Seattle, WA, USA
2Department of Geography, University of Sheffield, Sheffield, UK
3Norwegian Meteorological Institute, Blindern, 0313 Oslo, Norway
4Korea Polar Research Institute, Incheon, Republic of Korea
5International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK, USA
6Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA, USA
7Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA
November 26, 2013
- Fall 2012 was anomalously warm over the Arctic Ocean and adjacent lands after the record sea ice loss in summer 2012.
- Anomalously low winter temperatures in Eurasia were followed by anomalously high spring temperatures in Eurasia and the adjacent Arctic Ocean, while anomalously high winter temperatures over the central Arctic Ocean, Greenland and Baffin Bay were followed by anomalously low spring temperatures in Greenland, northern Canada and Alaska.
- The summer 2013 mean sea level pressure field was characteristic of a positive Arctic Oscillation/North Atlantic Oscillation. Consequently, relative to the previous six years, air temperatures were anomalously low across the central Arctic Ocean, Greenland and northern Canada. In contrast, summer 2013 in Alaska was one of the warmest on record.
Mean Annual Surface Air Temperature
Calendar year 2012 is the most recent year for which data are available for all months. The mean annual air temperature in 2012 was slightly lower than in 2011, but it was still sixth warmest year observed in the Arctic since the early 20th Century (Fig. 1). At the time of writing, the period January-August 2013 was the second warmest such period on record since the beginning of the 20th Century.
The first twelve years of the 21st Century (2001-2012) have been much warmer than the 1971-2000 baseline period at the end of the 20th Century (Fig. 2). Positive (warm) anomalies occurred in all parts of the Arctic, an indication that the early 21st Century temperature increase is due to global warming rather than natural regional variability (Jeffries et al. 2013). Over a longer time interval, the annual mean surface air temperature over Arctic land areas has experienced a warming of about +2°C since the mid-1960s (Fig. 1). This temperature increase is a manifestation of "Arctic Amplification", which is characterized by increases 1.5°C greater than (more than double) the increases at lower latitudes (Overland et al. 2011, Stroeve et al. 2012).
Seasonal Surface Air Temperature Variability, October 2012 to August 2013
Seasonal air temperature variations are described for the period October 2012 to August 2013, i.e., the period since temperatures were last reported in Arctic Report Card 2012 (Jeffries et al. 2012), and the last month for which data were available at the time this essay was written. This 11-month period is divided into fall 2012 (October, November, December), winter (January, February, March), spring (April, May) and summer (June, July, August) of 2013.
In fall 2012 there were anomalously high air temperatures over the Arctic Basin and adjacent lands, particularly Eurasia (Fig. 3a) and northernmost Canada. This is consistent with a large release of heat associated with the cooling and freezing of the very extensive area of open water that occurred in summer 2012, when there was a record low sea ice extent (Perovich et al. 2012).
In contrast, an elliptically shaped region of low temperature anomalies stretched from central Canada to Alaska (Fig. 3a), where the temperature in parts of Interior Alaska was more than 6°C lower than normal in November. Subsequently, in winter 2013, Alaska enjoyed above normal winter temperatures and the Arctic Basin also remained anomalously warm (Fig. 3b). A very strong winter high temperature anomaly developed over the Baffin Bay region, with record high temperatures in March along the coast of west Greenland (see the essay on the Greenland Ice Sheet). In contrast, winter was particularly cold in Eurasia, from Scandinavia all the way across the continent to easternmost Siberia (Fig. 3b).
In spring 2013, the temperature anomaly pattern (Fig. 3c) was almost the opposite of the winter pattern (Fig. 3b). An area of anomalously low temperatures stretched from Iceland through Greenland and northern Canada to Alaska, where the Interior experienced the coldest April since 1924 and budburst/green-up of birch and aspen was the latest (26 May) since observations began in 1972 (Alaska Climate Research Center, 2013). In contrast, anomalously high temperatures occurred over much of the Arctic Basin and Eurasia (Fig. 3c), where a record low snow cover extent occurred in May (see the essay on Snow).
Eurasia remained anomalously warm in summer 2013 (Fig. 3d) and, in Alaska, an abrupt transition in late May to much-above normal temperatures heralded one of the hottest summers on record. For example, Fairbanks, in the Interior, experienced a record 36 days with temperatures of 27°C or higher. In contrast to Eurasia and Alaska, anomalously low temperatures occurred over northernmost Canada and Greenland (Fig. 3d). These conditions were associated with a geographically extensive low pressure field that is characteristic of a positive Arctic Oscillation/North Atlantic Oscillation (AO/NAO) (Fig. 4).
Summer 2013 Relative to the Summer Average of 2007-2012
The relative coolness of Greenland, northernmost Canada and the adjacent high Arctic Ocean in summer 2013 (Fig. 3d) is particularly evident when air temperature is compared to that of the period 2007-2012 (Fig. 5), when the six lowest minimum sea ice extents in the satellite record occurred (Perovich et al. 2012). The air temperatures across a broad swathe of the Arctic Ocean were 1-3°C lower than they were during 2007-2012 (Fig. 5). These relatively low temperatures are likely to have contributed to a notable increase in the minimum extent of the 2013 summer sea ice cover, relative to the record low in 2012. The 2013 minimum sea ice extent was the largest since 2006 (see the essay on Sea Ice). Similarly, 1-2°C lower temperatures over Greenland in summer 2013 (Fig. 5) contributed to lower surface melt extent and duration, and surface mass balance and river discharge (see the essay on the Greenland Ice Sheet).
Alaska Climate Research Center, 2013: May 2013 statewide summary. http://climate.gi.alaska.edu/Summary/Statewide/2013/May.
Jeffries, M. O., J. Richter-Menge and J. E. Overland (editors). 2012: Arctic Report Card 2012. http://www.arctic.noaa.gov/report12/.
Overland, J. E., K. R. Wood and M. Wang, 2011: Warm Arctic-cold continents: Impacts of the newly open Arctic Sea. Polar Res., 30, 15787, doi: 10.3402/polar.v30i0.15787.
Perovich, D. K., W. Meier, M. Tschudi, S. Gerland and J. Richter-Menge, 2012: Sea Ice, in Arctic Report Card 2012. http://www.arctic.noaa.gov/report12/sea_ice.html.
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.