Greenland ice loss season 2019 starts with a big melt spike
The summer months when Greenland loses more ice than it receives in snowfall (scientifically known as the ablation season) of 2019 began on June 13. This is very close to normal and actually one day later than the average date for the period 1981-2018. The onset of the summer ablation is defined as the first of three days in a row with more than one gigatonne mass loss across all of Greenland.
At DMI, we define the beginning of the ablation season as the first day of a period of at least three consecutive days where the surface mass balance (SMB) is negative and below –1 Gt/day (one gigatonne, Gt, is one billion tons and corresponds to 1 cubic kilometer of water or 400000 olympic size swimming pools). A negative SMB of 1 Gt therefore means that one Gt of ice is lost from the Greenland Ice Sheet. 100 gigatonnes contribute 0.28 mm to global sea level rise.
This week a wave of warmer temperatures across the Arctic including a spike in melting in Greenland on the 11th of June kicked off the ablation season. Although this is an average start date for the ablation season, 2019 actually was very close to starting much earlier, as climate scientist at DMI Peter Langen explains:
“In late May there was an early wave of melting associated with much warmer than average temperatures. There were two days in a row with more than 1 gigaton of ice lost from Greenland. Successive days saw melt, but just smaller than 1 Gt, and so this event didn’t quite make a new record for early ice loss. However, since then every day except one has had a negative SMB, so the ice loss from Greenland has actually been slow but steady since end-May.”
Despite a very snowy winter along the southeast coast of Greenland, the overall surface mass balance has been below average since a heavy snowfall event in mid-November. This helped to contribute to the second earliest start to the melt season on record as we wrote about earlier. Currently, the accumulated surface mass budget over the whole ice sheet is very low, much lower than the record-breaking high melt year of 2011-2012.
“The relatively dry winter means there is less snow to melt over most of the ice sheet compared to normal”, explains Ruth Mottram, a climate scientist and glaciologist at DMI. “The snow is brighter than the glacier ice underneath so it reflects more energy than the ice. When the snow is melted away though, the dark glacier ice starts to absorb more and the rate of melting speeds up. It’s a really important feedback that means the ice sheet may lose much more ice if the right weather conditions occur just because it has relatively little snow over most of the ice sheet”.
The albedo plots on the Polar Portal corroborate this finding and show that the ice sheet is much darker than usual for the time of year as a result of the early melting and low snowfall this year.
Martin Stendel, climate scientist at DMI, agrees but points out that conditions in the North Atlantic are very important to the local weather and how much melt can be expected. “If we see persistent positive NAO conditions this summer as we had in 2018, this circulation pattern is likely to put a brake on melting. However, in 2019 the NAO has been negative all the time since the beginning of May. Such a circulation pattern favors big melt events in Greenland like the one we are observing right now.” He further explains: “The situation is very similar to that observed in 2012 when there were very high melt rates over several days due to a blocking high pressure over the ice sheet”.
The similarities in the current weather situation with 2012 were also pointed out by polar portal scientist and sea ice researcher Rasmus Tonboe determined that the melt season for the Arctic sea ice started as early as in 2012. How extreme the situation for Arctic sea ice is can be seen on the photograph below that Steffen M. Olsen, oceanographer at DMI, took at the Inglefield Fjord in northwestern Greenland, situated close to 78°N.
The pattern of the above than average snowfall along the east coast (right panel) follows the pattern of the temperature distribution (left panel) displayed below. The figure shows the anomalies for the winter half year (November 2018 – April 2019) from the average 2004-2013. A classical “see-saw” can be seen, with temperatures above average over most of Europe and along Greenland’s east coast and cold conditions along the west coast of Greenland. Large parts of the high Arctic have also been warmer than average, in particular over the Canadian Archipelago and over Alaska.
The map below shows the accumulated ablation from September 1 to June 17 according to DMI’s surface mass balance model. Accumulation maps are updated once per week. The time series at the bottom shows the accumulated surface mass balance since September 1, 2018.
As can be seen, the surface mass balance of the season 2018/2019 is much lower than during the record year 2011/2012 at the same time. It is still too early to say how the ablation season 2019 will end, since almost all of the ablation takes place in July and August.
There is, however, a good chance for large ablation values during the summer. This is due to the fact that the albedo of the Greenland Ice Sheet has been much lower than average in the southern half of Greenland, in particular along the west coast where strongly negative anomalies have prevailed for more than six weeks now.
Polar Portal is a collaboration between DMI, GEUS, and DTU with funding from the Danish Energy Agency (Energistyrelsen).
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