Atmosphere Assessments

Aaron Letterly
23 March 2018

The Arctic: 2017 Begins and Ends with High Temperatures

The year 2017 began with widespread positive temperature anomalies, almost 5°C over the entire Arctic Ocean. Twin low pressure systems in the Gulf of Alaska and the North Atlantic set up prime conditions for warm southerly advection (Figure 1). Some areas near Novaya Zemlya and the Central Arctic affected by the warm air reached temperatures up to 10°C higher than their 1984-2013 average (Figure 2), according to the Extended Advanced Very High Resolution (AVHRR) Polar Pathfinder dataset (APP-x). Higher-than-usual temperatures continued through February and March, slowing sea ice growth and contributing to the lowest annual maximum extent in the 38-year satellite record. The large, low pressure feature over Siberia and the Arctic Ocean in March and early April led to continued southerly winds and higher temperatures in early spring over this region, while temperatures over the Alaskan and Canadian Arctic dropped to lower than normal. Pressure remained far below average in Siberia and the rest of the Eastern Hemisphere, but was higher than average over Greenland and the Canadian Arctic. This atmospheric pressure pattern produces a trans-polar airflow that extends from Alaska to Svalbard. This circulation is apparent in the sea ice motion vectors tracked from satellite (Figure 3).

Figure 1: Mean sea level pressure (mb) during January, 2016 from the NCEP/NCAR Reanalysis Version 1. Areas of low sea level pressure brought southerly winds into the Arctic from both the Atlantic and Pacific sectors. Data are from ClimateReanalyzer.org.

Figure 2: Monthly surface temperature anomaly for every month in 2017. Departures from average (in degrees Celsius) are compared to their 1984-2013 mean for that month. Data are from the APP-x dataset.

Figure 3: Sea ice motion January 15-16, 2017. The data show trans-polar sea ice motion across almost the entire Arctic. Higher brightness temperatures show the sea ice edge in the Northern Atlantic Ocean. This sea ice motion product is derived from Advanced Microwave Scanning Radiometer 2 (AMSR2) and Visible Infrared Imaging Radiometer Suite (VIIRS) data.

May and June were mixed, with surface temperatures generally higher over the Canadian Archipelago but lower-than-normal in the East Siberian Sea. Areas of the Chukchi and Bering Sea experienced intense northerly winds in April, which blew thin, first-year ice into warmer water where it promptly broke apart and melted (NSIDC). This setback would have major implications for sea ice concentration in this region for the rest of the year. Ice retreat in the Pacific Arctic continued throughout the summer due to above-average temperatures and early arrival of warm water in the Bering Sea. As summer came to a close, low atmospheric pressure over Northern Alaska helped push sea ice northward in the Beaufort and Chukchi Seas. Over the entire Arctic, however, circulation driven by the low pressure system spread the ice over a larger area which resulted in the eighth-lowest minimum sea ice area on September 13. By mid-October, positive surface temperature anomalies off of Greenland had stymied ice growth in much of the North Atlantic Arctic. On the Pacific side, warm water and winds from the south in November contributed to the extremely reduced sea ice extent in the Chukchi Sea. The warm conditions here persisted into 2018, and can be read about in Interesting Events.

Northern and Southern Hemispheres

Overall, 2017 was characterized by above-average temperatures in both hemispheres. It is the 41st consecutive year of land and ocean temperatures above their 20th century average and stands currently as the third-warmest year on record. Figure 4 shows yearly temperature anomalies in the left column, for the Northern and Southern hemispheres, with month-by-month temperature anomalies in the right column. Since the beginning of 2016, every month has had an average temperature anomaly of greater than 0.6°C in the Northern Hemisphere and greater than 0.5°C in the Southern Hemisphere.

Figure 4: Annual temperature anomaly for the Northern Hemisphere (top left) and Southern Hemisphere (bottom left). Monthly temperature anomaly for the Northern Hemisphere (top right) and Southern Hemisphere (bottom right) over all land and sea pixels from the beginning of 2016 through the end of 2017. Data are from the Climatic Research Unit in conjunction with the Hadley Centre (UK Met Office).

References

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Jones, P.D., Osborn, T.J., Briffa, K.R., Folland, C.K., Horton, B., Alexander, L.V., Parker, D.E. and Rayner, N.A., 2001: Adjusting for sampling density in grid-box land and ocean surface temperature time series. J. Geophys. Res. 106, 3371-3380, doi:10.1029/2000JD900564.

Jones, P.D., Lister, D.H., Osborn, T.J., Harpham, C., Salmon, M. and Morice, C.P., 2012: Hemispheric and large-scale land surface air temperature variations: an extensive revision and an update to 2010. Journal of Geophysical Research 117, D05127, doi:10.1029/2011JD017139.

Kennedy J.J., Rayner, N.A., Smith, R.O., Saunby, M. and Parker, D.E., 2011: Reassessing biases and other uncertainties in sea-surface temperature observations measured in situ since 1850 part 2: biases and homogenisation. Journal of Geophysical Research 116, D14104, doi:10.1029/2010JD015220.

Morice, C.P., Kennedy, J.J., Rayner, N.A. and Jones, P.D., 2012: Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: the HadCRUT4 dataset. Journal of Geophysical Research, 117, D08101, doi:10.1029/2011JD017187.

NOAA National Centers for Environmental Information, State of the Climate: Global Climate Report for Annual 2017, published online January 2018, retrieved on March 22, 2018 from https://www.ncdc.noaa.gov/sotc/global/201713.

NSIDC, 2018: Baked Alaska and 2017 in review, National Snow and Ice Data Center, http://nsidc.org/greenland-today/category/analysis/, January 3, 2018.

NSIDC, 2017: Warm Arctic cool continents, National Snow and Ice Data Center, http://nsidc.org/arcticseaicenews/2017/05/warm-arctic-cool-continents/, May 3, 2017.

NSIDC, 2017: Sluggish ice retreat, National Snow and Ice Data Center, http://nsidc.org/arcticseaicenews/2017/06/sluggish-ice-retreat/, June 7, 2017.

Osborn, T.J. and Jones, P.D., 2014: The CRUTEM4 land-surface air temperature data set: construction, previous versions and dissemination via Google Earth. Earth System Science Data 6, 61-68, doi:10.5194/essd-6-61-2014.

Woodgate et al, 2017, Bering Strait 2017 Norseman II Cruise report, July 22, 2017.