Den stora tråden om global uppvärmning/växthuseffekten

Polar Portal Season Report 2018

Unusual weather resulted in an atypical melting season in the Arctic

The 2017-18 season in the Arctic has once again been extraordinary. A cold summer with high levels of precipitation has benefitted the Ice Sheet, whilst glaciers have continued the development seen during the last six years in which they have more or less maintained their area. The sea ice, on the other hand, has been more vulnerable, with high sea temperatures and warm winds leading to a large area north of Greenland being ice-free in two separate periods – February and August respectively.

The heatwave in Europe and the cold Greenlandic summer are connected through the Atlantic “seesaw”

Many people in the Northern Hemisphere – and in particular northern Europe – will remember the record-breaking heat and drought of the summer of 2018. In contrast, Greenland had a rather cold and snowy summer, particularly in June and at the end of August, when a major storm dumped large amounts of snow on the Ice Sheet.

As early as AD 1230, a Norwegian book called “The King’s Mirror” contained a description of the correlation between stormy weather over the eastern Atlantic and cold air, which is “sucked down” from the Ice Sheet to inhabited areas. Much later, in the 1770s, Danish missionary Hans Egede observed that “when the winter in Denmark was severe, as we perceive it, the winter in Greenland in its manner was mild, and conversely. In other words, the “seesaw” connection between warm weather in Europe and cold weather in Greenland (and vice versa) has been a recognised phenomenon for centuries. And the summer of 2018 was a particularly clear example of this circulation anomaly.

From the end of April until mid-October, a circulation pattern in the form of the Greek capital letter Ω over Scandinavia was prevailing most of the time. This type of circulation “blocks” the normal westerlies, and while warm air moves north across large parts of northern Europe, cold air from the central Arctic is present over Iceland and Greenland. This pattern is seen most clearly in the map of temperature anomalies for May
2018 shown below. But the same circulation anomaly was present during the other months as well.

In the following, we will look at the most important results monitored in the Arctic in 2018:

• The wettest May in Greenland since 1949
• As in the previous year, 2018 was yet another year with a low degree of
melting of the Ice Sheet
• The albedo of the Ice Sheet was recordhigh in May, June and the beginning of
August
• Two unusual openings in the sea ice north of Greenland in 2018
• Small changes in the area of the glaciers
• Still no data from GRACE Follow-On