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Atmosphere Assessments

2018

Aaron Letterly
9 July 2019

The Arctic: Extreme Late-Season High Temperatures

During each month of 2018, the average Arctic surface temperature was 0.5°C above the corresponding 30-year surface temperature mean (1984-2013). Month-by-month surface temperature anomalies are shown in Figure 1.

Figure 1: Animation of monthly surface temperature anomaly for each month in 2018. Departures from average are compared to their 1984-2013 mean for that month. Data are from the AVHRR Polar Pathfinder Extended (APP-x) dataset.

On the Atlantic sector of the Arctic sea ice edge, surface temperatures near Svalbard and Greenland were almost 10°C above average throughout January and February according to the AVHRR Polar Pathfinder Extended (APP-x) dataset. Similarly, on the opposite side of pole, temperatures south of the Bering Strait were more than 10°C above average. The high temperatures over the marginal ice zones persisted through March and into April. By May, surface temperatures over much of the central Arctic Ocean had returned to normal. Surface temperatures over Alaska, northern Canada, and parts or northern Europe and western Russia were below average in the spring and early summer. In June, a large area of Russia spanning from south of the Laptev sea to Lake Baikal experienced temperatures more than 10°C above average. These extreme temperatures resulted in enhanced sea ice loss throughout the Siberian Arctic. By the end of the summer in September, the seas surrounding the Canadian Archipelago and Greenland were the only areas of the Arctic Ocean where surface temperatures were less than 3-5° above average. As temperature anomalies of over 10°C persisted throughout October and November over parts of the Laptev, Chukchi, and Beaufort Sea, the autumn freeze-up arrived slowly in much of the Arctic, which experienced its third overall lowest October sea ice area in 2018. Before the temperatures decreased in November, hundreds of kilometers of open water extended as far as 80°N in the Siberian sector. By the end of December 2018, higher-than-average surface temperatures had resulted in the third-lowest December sea ice extent in the satellite record (NSIDC).

The month-by-month temperature anomalies relative to the last few years are shown for both the Northern and Southern hemispheres in Figure 2. The annual surface temperature from 1850 to 2018 is also shown. This is the 42nd consecutive year of land and ocean temperatures above their 20th century average. In the Southern Hemisphere, each month since the beginning of 2018 was more than 0.7° C above average.

Figure 2: 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 2018. Data are from the Climatic Research Unit in conjunction with the Hadley Centre (UK Met Office).

Antarctic: Below-average Temperatures for Much of the Year

The Antarctic reached its sea ice minimum around 20 February 2018, which was the second-lowest total on the satellite record (National Snow and Ice Data Center). During this time, Antarctic surface temperatures were only 2-4 degrees above their climatological average. Below-average temperatures in March and April over the Ross Ice Shelf resulted in above-average ice growth for that time of year. Sea ice continued to grow at an accelerated rate through part of June, but slowed by the end of the month and into July as warm northern winds brought increased temperatures over much of the sea ice area. By August, sea ice extent was lower than 90% of observed years (NSIDC). Even though the October 2018 sea ice extent was approximately 3.5 million km2 lower than it was 35 years ago, surface temperatures over parts of Antarctica were up to 10°C cooler in 2018 than 1983 (Figure 3). Lower-than-average surface temperatures in conjunction with a low Antarctic sea ice area help to point out that Arctic versus Antarctic sea ice changes are influenced differently by such physical properties as geography, wind, and air/sea surface temperature. By the end of 2018, Antarctic sea ice had reached the minimum extent for December 31st over the satellite record.

Figure 3: Air surface temperature for October 2018 (left) versus October 1983 (right). Though continental temperatures were 5-10°C cooler in 2018, ice extent was only 61% of its October 1983 total (NSIDC). Data are from the APP-x dataset.

References

Jones, P.D., New, M., Parker, D.E., Martin, S. and Rigor, I.G., 1999: Surface air temperature and its variations over the last 150 years. Reviews of Geophysics 37, 173-199, doi:10.1029/1999RG900002.

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.

NSIDC, 2018: A record-low start to the new year in Antarctica, National Snow and Ice Data Center, https://nsidc.org/arcticseaicenews/2019/01/a-record-low-start-to-the-new-year-in-antarctica/, January 3, 2019.

NSIDC, 2017: Ice loss speeds up during second half of July, National Snow and Ice Data Center, https://nsidc.org/arcticseaicenews/2018/08/ice-loss-speeds-up-during-second-half-of-july/, August 2, 2018.

NSIDC, 2017: A sluggish June, National Snow and Ice Data Center, https://nsidc.org/arcticseaicenews/2018/07/a-sluggish-june/, July 4, 2018.

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.