From the 1960s to the 1980s an area in the
North Atlantic which included southern Greenland was one of the few locations in the world which showed cooling rather than warming. This location was relatively warmer in the 1930s and 1940s than in the decades immediately before or after. More complete data sets have established trends of warming and ice loss starting from 1900 (well after the start of the
Industrial Revolution and its impact on global carbon dioxide levels) and a trend of strong warming starting around 1979, in line with concurrent observed
Arctic sea ice decline. In 1995–1999, central Greenland was already warmer than it was in the 1950s. Between 1991 and 2004, average winter temperature at one location, Swiss Camp, rose almost . Consistent with this warming, the 1970s were the last decade when the Greenland ice sheet grew, gaining about 47
gigatonnes per year. From 1980–1990 there was an average annual mass loss of ~51 Gt/y. and temperatures there had been the highest in the entire past last millennium – about warmer than the 20th century average. Several factors determine the net rate of ice sheet growth or decline. These are: • Accumulation and melting rates of snow in and around the centre • Melting of ice along the sheet's margins •
Ice calving into the sea from outlet glaciers also along the sheet's edges When the
IPCC Third Assessment Report was published in 2001, the analysis of observations to date had shown that the ice accumulation of 520 ± 26 gigatonnes per year was offset by runoff and bottom melting equivalent to ice losses of 297±32 Gt/yr and 32±3 Gt/yr, and
iceberg production of 235±33 Gt/yr, with a net loss of −44 ± 53 gigatonnes per year. Annual ice losses from the Greenland ice sheet accelerated in the 2000s, reaching ~187 Gt/yr in 2000–2010, and an average mass loss during 2010–2018 of 286 Gt per year. Half of the ice sheet's observed net loss (3,902 gigatons (Gt) of ice between 1992 and 2018, or approximately 0.13% of its total mass Between 2012 and 2017, it contributed 0.68 mm per year, compared to 0.07 mm per year between 1992 and 1997. Greenland's net contribution for the 2012–2016 period was equivalent to 37% of sea level rise from
land ice sources (excluding thermal expansion). These melt rates are comparable to the largest experienced by the ice sheet over the past 12,000 years. 3 of ice weighs about 0.9 Gt). In 2006, estimated monthly changes in the mass of Greenland's ice sheet suggest that it is melting at a rate of about per year. --> Currently, the Greenland ice sheet loses more mass every year than the
Antarctic ice sheet, because of its position in the
Arctic, where it is subject to intense
regional amplification of warming. Ice losses from the
West Antarctic Ice Sheet have been accelerating due to its vulnerable
Thwaites and
Pine Island Glaciers, and the Antarctic contribution to sea level rise is expected to overtake that of Greenland later this century. Between 1998 and 2006, thinning occurred four times faster for coastal glaciers compared to the early 1990s, while the landlocked glaciers experienced almost no such acceleration. One of the most dramatic examples of thinning was in the southeast, at
Kangerlussuaq Glacier. It is over long, wide and around thick, which makes it the third largest glacier in Greenland. Its observed ice flow speed went from per year in 1988–1995 to per year in 2005, which was then the fastest known flow of any glacier. The retreat of Kangerlussuaq slowed down by 2008, and showed some recovery until 2016–2018, when more rapid ice loss occurred. Greenland's other major outlet glaciers have also experienced rapid change in recent decades. Its single largest outlet glacier is
Jacobshavn Isbræ () in west Greenland, which has been observed by glaciologists for many decades. It historically sheds ice from 6.5% of the ice sheet In July 2012, Petermann glacier lost another major iceberg, measuring , or twice the area of
Manhattan. As of 2023, the glacier's ice shelf had lost around 40% of its pre-2010 state, and it is considered unlikely to recover from further ice loss. In the early 2010s, some estimates suggested that tracking the largest glaciers would be sufficient to account for most of the ice loss. However, glacier dynamics can be hard to predict, as shown by the ice sheet's second largest glacier,
Helheim Glacier. Its ice loss culminated in rapid retreat in 2005, associated with a marked increase in
glacial earthquakes between 1993 and 2005. Since then, it has remained comparatively stable near its 2005 position, losing relatively little mass in comparison to Jacobshavn and Kangerlussuaq, although it may have eroded sufficiently to experience another rapid retreat in the near future. Meanwhile, smaller glaciers have been consistently losing mass at an accelerating rate, and later research has concluded that total glacier retreat is underestimated unless the smaller glaciers are accounted for.
Processes accelerating glacier retreat front, with an increase in velocity spread across the mass of the glacier. 1997 also saw a shift in
circulation which brought relatively warmer currents from the
Irminger Sea into closer contact with the glaciers of West Greenland. By 2016, waters across much of West Greenland's coastline had warmed by relative to 1990s, and some of the smaller glaciers were losing more ice to such melting than normal calving processes, leading to rapid retreat. Conversely, Jacobshavn Isbrae is sensitive to changes in ocean temperature as it experiences elevated exposure through a deep subglacial trench. This sensitivity meant that an influx of cooler ocean water to its location was responsible for its slowdown after 2015, Likewise, the rapid retreat and then slowdown of Helheim and Kangerdlugssuaq has also been connected to the respective warming and cooling of nearby currents. At Petermann Glacier, the rapid rate of retreat has been linked to the topography of its grounding line, which appears to shift back and forth by around a kilometer with the tide. It has been suggested that if similar processes can occur at the other glaciers, then their eventual rate of mass loss could be doubled. and reach the base of the ice sheet There are several ways in which increased melting at the surface of the ice sheet can accelerate lateral retreat of outlet glaciers. Firstly, the increase in
meltwater at the surface causes larger amounts to flow through the ice sheet down to
bedrock via
moulins. There, it lubricates the base of the glaciers and generates higher basal pressure, which collectively reduces friction and accelerates
glacial motion, including the rate of
ice calving. This mechanism was observed at Sermeq Kujalleq in 1998 and 1999, where flow increased by up to 20% for two to three months. However, some research suggests that this mechanism only applies to certain small glaciers, rather than to the largest outlet glaciers, and may have only a marginal impact on ice loss trends. Secondly, once meltwater flows into the ocean, it can still impact the glaciers by interacting with ocean water and altering its local circulation - even in the absence of any ocean warming. While the models generally consider the impact from meltwater run-off as secondary to ocean warming, observations of 13 glaciers found that meltwater plumes play a greater role for glaciers with shallow grounding lines. Further, 2022 research suggests that the warming from plumes had a greater impact on underwater melting across northwest Greenland. Finally, it has been shown that meltwater can also flow through cracks that are too small to be picked up by most research tools - only wide. Such cracks do not connect to bedrock through the entire ice sheet but may still reach several hundred meters down from the surface. Their presence is important, as it weakens the ice sheet, conducts more heat directly through the ice, and allows it to flow faster. This recent research is not currently captured in models. One of the scientists behind these findings, Alun Hubbard, described finding moulins where "current scientific understanding doesn't accommodate" their presence, because it disregards how they may develop from hairline cracks in the absence of existing large
crevasses that are normally thought to be necessary for their formation.
Observed surface melting Currently, the total accumulation of ice on the surface of Greenland ice sheet is larger than either outlet glacier losses individually or surface melting during the summer, and it is the combination of both which causes net annual loss. Every summer, a so-called snow line separates the ice sheet's surface into areas above it, where snow continues to accumulate even then, with the areas below the line where summer melting occurs. The exact position of the snow line moves around every summer, and if it moves away from some areas it covered the previous year, then those tend to experience substantially greater melt as their darker ice is exposed. Uncertainty about the snow line is one of the factors making it hard to predict each melting season in advance. A notable example of ice accumulation rates above the snow line is provided by
Glacier Girl, a
Lockheed P-38 Lightning fighter plane which had crashed early in
World War II and was recovered in 1992, by which point it had been buried under of ice. Another example occurred in 2017, when an
Airbus A380 had to make an
emergency landing in
Canada after one of its
jet engines exploded while it was above Greenland; the engine's massive air intake fan was recovered from the ice sheet two years later, when it was already buried beneath of ice and snow. While summer surface melting has been increasing, it is still expected that it will be decades before melting will consistently exceed snow accumulation on its own. By 2019, it was found that while there was an increase in snowfall over southwest Greenland, there had been a substantial decrease in precipitation over western Greenland as a whole. Further, more precipitation in the northwest had been falling as rain instead of snow, with a fourfold increase in rain since 1980. Rain is warmer than snow and forms darker and less thermally insulating ice layer once it does freeze on the ice sheet. It is particularly damaging when it falls due to late-summer cyclones, whose increasing occurrence has been overlooked by the earlier models. There has also been an increase in
water vapor, which paradoxically increases melting by making it easier for heat to radiate downwards through moist, as opposed to dry, air. graphics show the extent of the then-record melting event in July 2012. Altogether, the melt zone below the snow line, where summer warmth turns snow and ice into slush and
melt ponds, has been expanding at an accelerating rate since the beginning of detailed measurements in 1979. By 2002, its area was found to have increased by 16% since 1979, and the annual melting season broke all previous records. and the ice sheet lost approximately 0.1% of its total mass (2900 Gt) during that year's melting season, with the net loss (464 Gt) setting another record. It became the first directly observed example of a "massive melting event", when the melting took place across practically the entire ice sheet surface, rather than specific areas. That event led to the counterintuitive discovery that
cloud cover, which normally results in cooler temperature due to their
albedo, actually interferes with
meltwater refreezing in the
firn layer at night, which can increase total meltwater runoff by over 30%. Thin, water-rich clouds have the worst impact, and they were the most prominent in July 2012. Ice cores had shown that the last time a melting event of the same magnitude as in 2012 took place was in 1889, and some glaciologists had expressed hope that 2012 was part of a 150-year cycle. This was disproven in summer 2019, when a combination of high temperatures and unsuitable cloud cover led to an even larger mass melting event, which ultimately covered over at its greatest extent. Predictably, 2019 set a new record of 586 Gt net mass loss. In July 2021, another record mass melting event occurred. At its peak, it covered , and led to daily ice losses of 88 Gt across several days. High temperatures continued in August 2021, with the melt extent staying at . At that time, rain fell for 13 hours at Greenland's Summit Station, located at elevation. Researchers had no
rain gauges to measure the rainfall, because temperatures at the summit have risen above freezing only three times since 1989 and it had never rained there before. Due to the enormous thickness of the central Greenland ice sheet, even the most extensive melting event can only affect a small fraction of it before the start of the freezing season, and so they are considered "short-term variability" in the scientific literature. Nevertheless, their existence is important: the fact that the current models underestimate the extent and frequency of such events is considered to be one of the main reasons why the observed ice sheet decline
in Greenland and
Antarctica tracks the worst-case rather than the moderate scenarios of the
IPCC Fifth Assessment Report's
sea-level rise projections. Some of the most recent scientific projections of Greenland melt now include an extreme scenario where a massive melting event occurs every year across the studied period (i.e. every year between now and 2100 or between now and 2300), to illustrate that such a hypothetical future would greatly increase ice loss, but still wouldn't melt the entire ice sheet within the study period. These low temperatures are in part caused by the high
albedo of the ice sheet, as its bright white surface is very effective at reflecting sunlight.
Ice-albedo feedback means that as the temperatures increase, this causes more ice to melt and either reveal bare ground or even just to form darker melt ponds, both of which act to reduce albedo, which accelerates the warming and contributes to further melting. This is taken into account by the
climate models, which estimate that a total loss of the ice sheet would increase global temperature by , while Greenland's local temperatures would increase by between and . In 2018, it was found that the regions covered in
dust,
soot, and living
microbes and
algae altogether grew by 12% between 2000 and 2012. In 2020, it was demonstrated that the presence of algae, which is not accounted for by
ice sheet models unlike soot and dust, had already been increasing annual melting by 10–13%. Additionally, as the ice sheet slowly gets lower due to melting, surface temperatures begin to increase and it becomes harder for snow to accumulate and turn to ice, in what is known as surface-elevation feedback. , about half of which (around 0.3 million tons every year) is
bioavailable as a
nutrient for
phytoplankton. Thus, meltwater from Greenland enhances
ocean primary production, both in the local
fjords, and further out in the
Labrador Sea, where 40% of the total primary production had been attributed to nutrients from meltwater. Since the 1950s, the acceleration of Greenland melt caused by climate change has already been increasing productivity in waters off the North Icelandic Shelf, while productivity in Greenland's fjords is also higher than it had been at any point in the historical record, which spans from late 19th century to present. Some research suggests that Greenland's meltwater mainly benefits marine productivity not by adding carbon and iron, but through stirring up lower water layers that are rich in
nitrates and thus bringing more of those nutrients to phytoplankton on the surface. As the outlet glaciers retreat inland, the meltwater will be less able to impact the lower layers, which implies that benefit from the meltwater will diminish even as its volume grows. , or the annual anthropogenic emissions of around 40 billion tonnes of . There is one known area, at
Russell Glacier, where meltwater carbon is released into the atmosphere in the form of
methane (see
arctic methane emissions), which has a much larger
global warming potential than carbon dioxide. However, the area also harbours large numbers of
methanotrophic bacteria, which limit those methane emissions. In 2021, research claimed that there must be mineral deposits of
mercury (a highly
toxic heavy metal) beneath the southwestern ice sheet, because of the exceptional concentrations in meltwater entering the local
fjords. If confirmed, these concentrations would have equalled up to 10% of mercury in all of the world's rivers. In 2024, a follow-up study found only "very low" concentrations in meltwater from 21 locations. It concluded that the 2021 findings were best explained by accidental sample contamination with
mercury(II) chloride, used by the first team of researchers as a
reagent. However, there is still a risk of
toxic waste being released from
Camp Century, formerly a
United States military site built to carry
nuclear weapons for the
Project Iceworm. The project was cancelled, but the site was never cleaned up, and it now threatens to pollute the meltwater with
nuclear waste, 20,000 liters of
chemical waste and 24 million liters of untreated sewage as the melt progresses. /
NOAA; 20 January 2016). Finally, increased quantities of fresh meltwater can affect
ocean circulation. In 2016, a study attempted to improve forecasts of future AMOC changes by incorporating better simulation of Greenland trends into projections from eight state-of-the-art
climate models. That research found that by 2090–2100, the AMOC would weaken by around 18% (with a range of potential weakening between 3% and 34%) under
Representative Concentration Pathway 4.5, which is most akin to the current trajectory, == Future ice loss ==