Greenland melt season reaches full speed ahead
The summer months when Greenland loses more ice than it receives in snowfall (scientifically known as the ablation season) of 2020 began on June 22. This is 10 days later than the average date for the period 1981-2019. 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.
On the Polar Portal we use DMI’s definition of the beginning of the ablation season, 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 metric tonnes and corresponds to 1 cubic kilometer of water). A negative SMB of 1 Gt therefore means that one Gt of ice is lost from the Greenland Ice Sheet net of any ice gain from snow fall.
Although the melt season started close to normal and significant melt has continued since mid-May, a series of fresh snowfalls in different places across the ice sheet have balanced the loss of ice by melt and, temporarily brightened the surface which in turns leads to more reflection and a reduction in melt.
Martin Stendel, climate scientist at DMI, commented “although there have been very warm temperatures in other parts of the Arctic, Greenland has been largely close to average so far this year. There have been some pulses of extra high melt but these have been largely balanced by extra snow fall in other parts of the ice sheet. Some areas, especially western Greenland have seen very high melt rates though.”
Although this year’s onset of the ablation season was late (30th out of the 40 years in our record). the weather situation in July and August is the most important in determining how much ice melts over the year. Climate scientist Ruth Mottram, also at DMI, commented “while going into a summer with a low snow cover is important but if the summer is cool and cloudy or warm and sunny can make a very big difference to the ice budget.“
The map shows the ice sheet’s total surface gains and losses since 1 September 2019, compared to the period 1981-2010. It does not include the mass that is lost when glaciers calve off icebergs and melt as they come into contact with warm seawater. The line plots show the daily and accumulated surface mass balance averaged over all of Greenland. The blue curve shows the current season, whilst the red curve shows the corresponding development for the 2011-12 season, when the degree of melting was record high. The dark grey curve traces the mean value from the period 1981-2010, while the light grey band shows differences from year to year. For any calendar day, the band shows the range over the 30 years (in the period 1981-2010), however with the lowest and highest values for each day omitted.
Polar portal partners at GEUS use satellite observations as well as weather stations on the ice sheet to measure the brightness of the ice sheet which in turn is also used in our climate models to improve our estimates of surface mass budget.
Their data shows that the spike in brightness after each snowfall very quickly disappears, meaning that the snow cover is rather thin. Professor Jason Box, senior scientist at GEUS, comments “although the ablation season onset has been delayed this year, our data show that melt has been pretty intense over the ice sheet since June and the relatively dry winter means if we get another warm spike this year, as we did in 2019, there may well be very high ice loss from the ice sheet this year.”
Although Greenland is currently Corona free after a handful of cases in the early Spring, the Promice group are taking no chances with their fieldwork this year “we have scaled back our fieldwork as much as possible to reduce the risk of carrying the virus back to Greenland, fortunately we can do a lot of work remotely and our network has been set up to be very robust” said Robert Fausto, PROMICE lead at GEUS.
Polar Portal is a collaboration between DMI, GEUS and DTU with funding from Dancea (Danish Cooperation for Environment in the Arctic) under the Danish Ministry for Energy, Utilities and Climate.
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