Guest post: How the Greenland ice sheet fared in 2021
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46% OffAs meltwater refreezes in the snow, it can be seen as a thin layer of ice in a shallow ice core that consists of layers of snow and firn– the intermediate phase before snow ends up being compressed into glacier ice. Summer and winter season snow look various in such a core, so we can count the years and, for that reason, find in which year the melt occurred..
This year was likewise noteworthy for the very first tape-recorded rainfall at the top of Greenland, which is 3,200 metres above water level. And a new velocity of ice loss at Sermeq Kujalleq– sometimes understood as Jakobshavn Isbræ or Ilulissat glacier.
Despite the cool start, as the melt season got underway there was a duration of very high temperatures at the end of July. This brought intense melt all around the ice sheet that caused very big ice losses over a couple of days..
This is also the very first time given that direct observations began in 2008 that rain was seen by personnel at the station.
As ever with our annual Greenland review, we focus on the 12 months up until completion of August..
Sermeq Kujalleq on 22 August 2021, drawn from ESA Sentinel-2 image processed in the shortwave and infrared bands on Sentinel Hub. The glacier sped up and calved substantially in 2020-21, losing around 45Gt of ice. Credit: Modified Copernicus Sentinel information 2021/Sentinel Hub.
Greenlands yearly cycle sees the ice sheet mostly get snow from September, building up ice through autumn, winter season and into spring. Then, as the year heats up into late spring, the ice sheet begins to lose more ice through surface melt than it gains from fresh snowfall. This melt season usually continues up until the end of August..
Winter season snowfall over 2020-21 was close to average, which is good news for the health of the ice sheet. For example, low winter season snowfall in mix with warm summers– as in 2019– can lead to really high ice losses..
The map below programs the area of ice melt on 28 July (red shading), and the chart below validates that more than 60% of the ice sheets surface was melting on that day.
Accounting for both surface melting and discharge of icebergs, the Greenland ice sheet lost around 166bn tonnes of ice over the 12-month period ending in August. This indicates that 2021 is the 25th year in a row where Greenland has actually lost more ice than it gained.
Although this year was not a record ice loss year in Greenland, when we also account for calving, it was still the 25th year in a row where the ice sheet lost more ice than it acquired..
( See our previous yearly analysis for 2020, 2019, 2018, 2017, 2016 and 2015.).
While a rapid-attribution study revealed that such an extreme event would have been “essentially difficult” without the underlying impact of human-caused warming, it was mostly driven by a meandering jet stream..
Rain suggests temperatures near or above the freezing point and melting at Summit is a really unusual occasion..
Rain at the top.
Combining these losses with the SMB gives a “total mass balance” for the year.
The science tech up at Summit did make direct observations of rain on August 14. I can provide you more information!: Alicia Bradley, NSF. 6am, rain observed. pic.twitter.com/hGnFvRm0yT— Zoe Courville (@ZoeCourville) August 19, 2021.
When the satellite records started, this method shows that the year 2020-21 had the greatest loss of ice to calving and ocean melt since at least 1986.
The factor for the wet and cold early summertime over the Greenland ice sheet can be discovered rather far, over south-western Canada and north-western US, which experienced a record-breaking “heat dome” at the end of June and the beginning of July.
The snow gains and ice losses at the ice sheets surface area over the previous 12 months is Greenlands “surface mass balance” (SMB). Listed below, the blue line in the leading and bottom charts show the everyday SMB and cumulative SMB for 2020-21, respectively. The grey line shows the red line and the long-term average shows the record low year of 2011-12 for contrast.
Leading: Map showing areas of Greenland going through surface area melt on 28 July 2021 (shaded red). Bottom: Chart revealing portion of ice sheet location seeing surface melt on every day of 2021 (blue line), ending on the 28 July. The grey line shows the 1981-2010 average. Credit: DMI Polar Portal.
According to our calculations, this year the Greenland ice sheet ended with an overall SMB of about 396bn tonnes (Gt). This implies that the period September 2020 to August 2021 ranks as 28th least expensive out of a 41-year timeseries. In the existing environment, this can be considered a relatively typical year. However, in the late 90s, this would be viewed as a very low year.
Significantly, in 2020-21, Sermeq Kujalleq– likewise known as the Jakobshavn Isbræ or Illulissat glacier, the fastest glacier on the planet– has accelerated once again after a few peaceful years. At the very same time the glacier produced a big amount of icebergs and we calculate it lost around 45Gt in the last year– more than 10% of the yearly surface area mass spending plan. This has a huge influence on the total ice spending plan for the year.
In this guest post, we decipher the processes of ice sheet melt, glacier calving, weather condition and environment that describe these losses.
The map listed below shows how the geographic spread of SMB gains (blue) and losses (red) for 2020-21 compare to the long-lasting average..
Sharelines from this story.
Over the western part of Canada and the US, a substantial “obstructing” high pressure system formed. Shaped like the capital Greek letter Omega (Ω), such a flow pattern happens frequently, however has actually never in the past been observed with such a strength..
Utilizing satellites, we can measure the speed at which ice flows through control points– locations around the edges of the ice sheet where we understand the thickness and shape of the ice. Integrated with data on how thick the ice is, we can estimate quite well the quantity of ice being lost by the procedure of calving and submarine melting. This information is now processed in near genuine time and is freely offered, enabling us to monitor the entire ice sheet budget.
Greenlands yearly cycle sees the ice sheet mainly acquire snow from September, accumulating ice through fall, winter and into spring. As the year warms up into late spring, the ice sheet begins to lose more ice through surface area melt than it acquires from fresh snowfall. The snow gains and ice losses at the ice sheets surface over the past 12 months is Greenlands “surface area mass balance” (SMB). Blue programs more ice gain than red and typical programs more ice loss than average. Utilizing satellites, we can measure the speed at which ice flows through control points– locations around the edges of the ice sheet where we know the thickness and shape of the ice.
Overall losses.
Provided the calving and ocean melt losses from Greenland this year, we were lucky the surface mass spending plan was so high, increasing snowfall and cool summer seasons will not always help to stabilize the ice budget plan.
In the summer season period, near-record snowfall in early June postponed the beginning of the primary part of the melt season. As fresh snow is intense white and shows sunshine better than the old dark glacier ice below, melt was low at the start of the melt season. It was also rather cool and wet in June and early July.
Over the previous 2,000 years, melt layers are just seen nine times: in 2021, 2019, 2012– these three were also straight observed by the station personnel– and prior to that in 1889, 1094, 992, 758, 753 and 244. The hottest observed temperature level at Summit was 2.2 C on 13 July in 2012..
Map revealing cool, damp summertime weather in Greenland (in centre of map) and the severe heat over North America. Shading shows temperature levels that are warmer (red) or cooler (blue) than the long-term average for the time of year.
The jet stream was diverted far to the north into the Canadian Arctic. At the “feet” of the Omega, troughs of low pressure– in this case one over Alaska and the other one over Greenland– resulted in the rather cool and damp summer..
This year, the Greenland ice sheet has provided a feast for researchers.
The records of Summit Station go back only to the 1990s, the absence of refrozen water layers in the snow and ice cores taken here reveal that rain is unlikely to have actually ever occurred at the top of the ice sheet since at least the 1880s..
The other impressive occasion of summer season 2021 was the rains at Greenlands Summit Station, literally on the top of Greenland, on 14 August. This is a very remote location– 3,216 metres above water level and with an annual average temperature of -30 C..
A damp and cool early summertime with late and unusually large snowfall in June postponed the onset of the main melt season– which generally runs through the northern hemisphere summer season– however a heatwave in late July subsequently brought greater ice loss..
Closer examination of the weather condition and ice sheet modifications expose some fascinating events and patterns.
Rain was a continuing style of the 2020-21 summer season. Qaqortoq in south Greenland taped a brand-new record daily rainfall of 145mm on the summer season solstice (and Greenland National Day), while the summer season likewise saw floods in the town of Qaanaaq in north-west Greenland.
The map below programs the cool, damp summertime weather in Greenland (in the centre of the map, shaded blue) in late June and the abnormal heat over the western half of North America (red shading on left-hand side).
The eastern Greenland airport community of Nerlerit (likewise known as “Constable Pynt”)– near to Ittoqqortoormiit (formerly referred to as “Scoresbysund”)– recorded a brand-new record high of 23.4 C at this time.
A “favorable” SMB– where the ice sheet gains more snow than it loses in ice– is the only ways by which the Greenland ice sheet can get ice. It likewise loses ice by other procedures, such as the “calving”– or breaking off– of icebergs, melting undersea at the front of glaciers where they meet the ocean, and to a small level by “basal melting” below the ice sheet as the ice slides over the ground.
The total mass balance for 2020-21 is a loss of around 166Gt of ice from Greenland– near the average ice lost each year for the duration 1986-2021..
Blue programs more ice gain than average and red programs more ice loss than average.: Daily (upper chart) and cumulative (lower) SMB of the Greenland ice sheet, in billion tonnes per day, and billion tonnes, respectively.
Blocking event.
Surface melt.
This implies that, from 1 September 1986 to 31 August 2021, we calculate the Greenland Ice Sheet has actually lost roughly 5,500 Gt of ice. This is equivalent to 1.5 cm of worldwide average water level rise.