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Effects & Impacts: Greenland melting

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Greenland melting

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Summary

The models used by the Intergovernmental Panel on Climate Change predict a sea level rise contribution from Greenland of around 10 centimeters by 2100, with a worst-case scenario of 15cm. But that prediction is at odds with what field scientists are witnessing from the ice sheet itself. According to our findings, Greenland will lose at least 3.3% of its ice. This loss is already committed – ice that must melt and calve icebergs to reestablish Greenland’s balance with prevailing climate.” – Alun Hubbard Professor of Glaciology, Arctic Five Chair, University of Tromsø, August 2022

“The glacier in Greenland’s largest drainage basin is thinning and its flow is accelerating. Updated simulations suggest that sea-level rise will be up to fivefold higher than previously expected.”Khan et al, November 2022

“Greenland’s glaciers are retreating everywhere and all at once. A comprehensive analysis of satellite data finds that the Greenland ice sheet has lost more ice in the past four decades than previously thought.” – Nature briefing, January 2024

“It is clear that the majority of models underestimated the rate of Greenland melt.” Bradley et al, July 2024

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Home > Climate wiki > Effects > Greenland melting

Summary

The models used by the Intergovernmental Panel on Climate Change predict a sea level rise contribution from Greenland of around 10 centimeters by 2100, with a worst-case scenario of 15cm. But that prediction is at odds with what field scientists are witnessing from the ice sheet itself. According to our findings, Greenland will lose at least 3.3% of its ice. This loss is already committed – ice that must melt and calve icebergs to reestablish Greenland’s balance with prevailing climate.” – Alun Hubbard Professor of Glaciology, Arctic Five Chair, University of Tromsø, August 2022

“The glacier in Greenland’s largest drainage basin is thinning and its flow is accelerating. Updated simulations suggest that sea-level rise will be up to fivefold higher than previously expected.”Khan et al, November 2022

“It is clear that the majority of models underestimated the rate of Greenland melt.” Bradley et al, July 2024

    • A new integrated model including the complex interactions between ice sheets, oceans and the atmosphere found that West Antarctica and Greenland will cross irreversible thresholds if global temperatures reach 1.8°C even temporarily, committing these ice sheets to increased ice loss and accelerating sea-level rise for several centuries.
    • If the recent observed acceleration of loss in Greenland were to continue, it would track above the upper range predicted by the IPCC (2021) for this decade.
    • The frequency and intensity of extreme events is also increasing over Greenland. Rainfall on the Greenland Ice Sheet has grown by a third since 1991, and the frequency of extreme deluges are increasing. Water quickly drains into the ice sheet through vast networks of micro-cracks that may run hundreds of meters deep, carrying surface water to deeper parts of the ice sheet and melting it from within. These extreme melt events may increase sea level rise projections from Greenland by up to 14% over previous worse-case scenarios by the year 2300, contributing as much as 3.74 meters to global sea-level rise.
    • Evidence from ancient soil recovered from beneath today’s ice sheet in northwest Greenland shows that 400,000 years ago, the ice sheet retreated over 200km inland, causing at least 1.4m sea-level rise from this section of Greenland alone, when CO2 concentrations were only 280ppm (today it’s more than 420ppm). This warming persisted for 30,000 years.
    • Overall: continued improvements in numerical modeling and scientific understanding of ice sheet processes shows that the Greenland and Antarctica ice sheets are more sensitive to warming than previously thought, and have the potential, resulting in rapid sea-level rise and at lower global mean temperatures than previously estimated.
    • Reference: State of the Cryosphere

The 2009 IPCC 4th Assessment Report stated that sea levels were not likely to be greatly affected by melting glaciers, Antarctica, Greenland, or anywhere else one Earth, in the twenty-first century.

However, the scientific scramble to understand events that were being witnessed since 1986 but failed to be predicted by the IPCC’s climate models was well underway. By the early 2000s, it was clear that Greenland was losing far more ice than it gained each year. In 2008, a year before the 2009 IPPC report, a staggering volume of ice on the leading edge (front) of the Jakobshaven Glacier on the south west coast (Fig. 1 map) was filmed as it carved spectacularly in just 75 minutes (Video 2). Then in 2010, a single iceberg 260km² x 213m deep broke off the Petermann Glacier (Fig. 1 map). By 2019, the amount of melting was finally being recognized by the IPCC:

“Summer melting of the Greenland Ice Sheet (GIS) has increased since the 1990s to a level unprecedented over at least the last 350 years, and two-to-five-fold faster than pre-industrial levels” IPCC, 2019

Video 2: 4 min. from the documentary ‘Chasing Ice’. The footage has not be slowed; the sheer scale of the icebergs breaking off Jakobshavn Glacier, which drains about 40% of Greenland’s icecap (Fig. 1 map), gives that impression.

Warming over Greenland in 2022 began much earlier than usual, following the trends shown in Figs. 4 & 5. This also accelerated melting permafrost and methane clathrates, adding greenhouse gases to the atmosphere. With each passing year, the rate of Arctic sea ice melting is accelerting, further destabilizing the jetstream and changing the world’s climate.

Fig. 4: Arctic temperature anomalies across the Arctic 13 May 2020. The temperatures are in Centigrade. Image: Computer model simulation (Karsten Haustein/Washington Post, 14 May 2020)
Fig. 5: Click on this screen grab to be taken to NASA’s National Snow and Ice Data Centre (NSIDC). Here you can select any year from 1979 to yesterday’s date (New Zealand is ahead by 18hrs, and there can be a delay over the weekend), to see the extend of melting on the Greenland ice cap. There are instructions on the landing page explaining how to do this. Note: the site does not operate properly using Internet Explorer.

How can it possibly melt this fast? The processes: warm air + warmer ocean

Note: the processes described below are the same as those described on the Antarctica page. The degree to which ‘top down’ melting from warming air temperatures (Fig. 6) and ‘bottom up’ melting from a warming ocean (Fig. 7) varies from place to place and over time.

“Rapid ice loss from the Greenland ice sheet since 1992 is due in equal parts to increased surface melting and accelerated ice flow. The latter is conventionally attributed to ocean warming, which has enhanced submarine melting of the fronts of Greenland’s marine-terminating glaciers. Yet, through the release of ice sheet surface meltwater into the ocean, which excites near-glacier ocean circulation and in turn the transfer of heat from ocean to ice, a warming atmosphere can increase submarine melting even in the absence of ocean warming.

“…we show that in south Greenland, variability in submarine melting was indeed governed by the ocean, but, in contrast, the atmosphere dominated in the northwest. At the ice sheet scale, the atmosphere plays a first-order role in controlling submarine melting and the subsequent dynamic mass loss.”  – Slater and Strano, October 2022

Video 3: How the ice sheet flows to outlet glaciers along Greenland’s coast

The Zwally effect: top down melting from warm air melts ice into giant meltwater lakes on the surface of glaciers (Fig. 6). This is causing around 34% of melting across Greenland. Thanks to their much lower albedo, like the ocean, the dark pools absorb more heat than the surrounding ice, causing more warming and hence further melting in a feedback effect. When this happens on ice shelves, the water finds crevasses in the ice, whereupon it drains down moulins (Video 4) that it scours out like a drill into the heart of glacier. Until the late 1990s it was assumed this water would re-freeze inside the glacier. Instead, through hydrofracturing, the weight and warm temperature of the water the moulin to widen as it drops, fracturing the ice at depth.

When this happens on marine glaciers or ice shelves (ie, sitting on the ocean), when the water reaches the base of the ice, the ice shelf is effectively turned into Swiss cheese and rapidly breaks up.

Whereas when this happens to glaciers sitting on land the outcome is different. If the glacier is on land that slopes downhill inland , when the meltwater reaches the bottom of the glacier, it lifts the glacier and/or joins with ocean water that has reached this point, adding to the melting and undercutting from below.

Where the glacier is on land that slopes downhill towards the ocean, the meltwater lubricates the glacier like a water slide, making it flow faster, which in turn opens or widens more crevasses, allowing yet more meltwater lakes to drain, and so on in a feedback effect. When this warm buoyant freshwater reaches the submerged terminus (front) of the glacier, it scours it from below, then shoots hundreds of metres up the terminus. In some instances it erupts at the surface in a churning jaccuzi-like swirl of mud and ice (Video 4).

Fig. 6: Meltwater lakes and dark snow dramatically reduce albedo, so heat is absorbed, which promotes further melting. (Image: Eli Kintisch).
Video 4: The spectacular ‘top down’ melting across Greenland’s ice cap
Fig. 7: From ‘The great Greenland meltdown’. Click image to read the Science magazine story (image: V. Altounian/Science)

Bottom up melting from relatively warm water originating from the Irminger Sea near Iceland, eats away at the underside of ice shelves (in some places over 2km deep), thinning them from below. This is causing around 66% of melting across Greenland. Continued undercutting allows more water to travel further under the ice shelf, eroding it and thinning it until it’s detached from the grounding line and the ice begins to float.

The Jakobshavn effect now comes into play (Video 5). As the thinning glacier become more buoyant, it floats at the calving front. And this means it’s forced to move up and down with the tides, effectively bending it up and down. These forces travel up the length of the glacier, ultimately assisting the leading edge to snap at the weakest point. Additionally, because the glacier is thinner at the front, the slope is steeper, so the glacial ice behind it speeds up due to gravity, allowing huge volumes of ice to surge downstream and into the sea (Fig. 8).

Each year since 2015, the (NASA) team has dropped about 250 probes into the ocean around the edge of Greenland. They’ve found the toasty waterup to 10°C or morenosed up to the end of glaciers around the island most of the time in most of the places…

“As they flew low over the leading edge of the massive Helheim glacier, aiming to drop a probe through a hole in the in the mélange of giant bergs floating at the glacier’s snout, they saw water roiling up through the hole “like a bubbling cauldron,” says Willis. When the probe pinged back data, it showed a warm wall of water extending straight down 2,000m to the bottom of the fjord: A solid wall of water ready to melt the glacier.” National Geographic, 2019

A small imbalance of forces caused by some perturbation can cause a substantial non-linear response.”Prof. Terry Hughes, ‘The Jakobshavn Effect’

Or as Prof. Jason Box puts it: “There are too many variables that determine exactly when a glacier calves. A single cracking event could conceivably be triggered by a seagull, acting like the straw that broke the camel’s back.”
Fig. 8: 'Bottom up' melting from an increasingly warmer ocean water has cause the leading edge of Jakobshaven Glacier to rapidly retreat. The ice is normally stabilized by sitting on the seafloor. As warm ocean currents eat away at the base, the ice thins, lifts away from the seafloor, and becoming unstable, breaks, losing its ability to act as a brake on the flow of ice from the ice cap inland.
Fig. 8: ‘Bottom up’ melting from an increasingly warmer ocean water has cause the leading edge of Jakobshaven Glacier to rapidly retreat. The ice is normally stabilized by sitting on the seafloor. As warm ocean currents eat away at the base, the ice thins, lifts away from the seafloor, and becoming unstable, breaks, losing its ability to act as a brake on the flow of ice from the ice cap inland.
Video 5: ‘Bottom up’ cooling. Between 2016 and 2017, Jakobshavn Glacier grew slightly and the rate of mass loss slowed because the ocean temperatures in the region cooled. In spite of this, melting across Greenland continued to accelerate as air temperatures increased and high pressure weather systems stalled, melting vast areas of the ice sheet. By 2019, the warm water had also returned.
Video 6: Arctic Report Card 2023
Video 7: Hurricane Fiona brings rain to Greenland 2022

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