The Greenland ice sheet is the second-largest ice sheet in the world. It is about 1,673 meters (or 5,489 feet) thick on average and as thick as 3,488 meters (or 11,444 feet) at its thickest point. The ice sheet stretches about 2,900 kilometers (or 1,800 miles) from north to south, and it is up to 1,100 kilometers (or 680 miles) wide near its northern edge. It covers an area of about 1,710,000 square kilometers (or 660,000 square miles), which is roughly 80% of Greenland’s surface and about 12% of the Antarctic ice sheet’s area. Scientists often call it GIS or GrIS in their research.

Greenland has had large glaciers and ice caps for at least 18 million years. However, a single ice sheet first covered most of the island about 2.6 million years ago. Since then, the ice sheet has grown and shrunk many times. The oldest ice found in Greenland is about 1 million years old. Because of greenhouse gases from human activities, the ice sheet is now the warmest it has been in the past 1,000 years. It is melting faster than it has in at least the past 12,000 years.

Each summer, parts of the ice sheet’s surface melt, and ice cliffs break off into the sea. Normally, snowfall in winter would replace the melted ice. However, because of global warming, the ice sheet is melting two to five times faster than it was before 1850. Since 1996, snowfall has not been enough to replace the ice that is melting. If the Paris Agreement goal of keeping global temperatures below 2°C (or 3.6°F) is met, melting from Greenland alone would raise sea levels by about 6 centimeters (or 2.5 inches) by the end of the century. If emissions are not reduced, melting would raise sea levels by about 13 centimeters (or 5 inches) by 2100. The worst-case scenario would add about 33 centimeters (or 13 inches). So far, melting has contributed about 1.4 centimeters (or 0.5 inches) to sea level rise since 1972, while all sources of sea level rise added between 15 and 25 centimeters (or 6 to 10 inches) between 1901 and 2018.

If all 2,900,000 cubic kilometers (or 696,000 cubic miles) of the Greenland ice sheet were to melt, it would raise global sea levels by about 7.4 meters (or 24 feet). If global temperatures rise between 1.7°C (or 3.1°F) and 2.3°C (or 4.1°F), melting the ice sheet would likely become unavoidable. Even if temperatures stay below 1.5°C (or 2.7°F), melting would still cause sea levels to rise by about 1.4 meters (or 4.5 feet). If temperatures rise above 1.5°C and then decrease, more ice would still be lost. If global temperatures continue to rise, the ice sheet could disappear in about 10,000 years. At very high temperatures, the ice sheet might disappear in about 1,000 years. Beneath the Greenland ice sheet are mountains and lake basins.

Description

Ice sheets form through a process called glaciation, which happens when the local climate is cold enough for snow to build up year after year. As snow layers pile up over time, their weight presses down on the snow below, turning it first into compacted snow, then into solid glacier ice over hundreds of years. The ice sheet in Greenland has remained about the same size as it is today. However, Greenland’s history includes 11 times when the ice sheet spread up to 120 km (75 mi) farther than it does now, with the most recent event occurring about 1 million years ago.

The heavy weight of the ice causes it to move slowly, unless it meets a large obstacle, like a mountain. Greenland has many mountains near its coast, which usually stop the ice sheet from moving into the Arctic Ocean. During the 11 earlier periods of glaciation, the ice sheet grew large enough to flow over these mountains. Today, the main areas where the ice sheet can flow into the ocean are the northwest and southeast edges, where the mountains have gaps that allow ice to leave through outlet glaciers. These glaciers regularly release pieces of ice into the ocean in a process called ice calving. Sediment from melted or broken ice settles on the seafloor, and sediment layers collected from places like the Fram Strait provide long records of Greenland’s history of glaciation.

Geological history

For most of the past 18 million years, Greenland had large glaciers, but these were likely similar to smaller modern glaciers, such as Maniitsoq and Flade Isblink, which cover 76,000 and 100,000 square kilometers (29,000 and 39,000 square miles) near the edges of the island. At first, Greenland’s conditions were not suitable for a single large ice sheet to form. However, around 10 million years ago, during the middle Miocene, the edges of West and East Greenland rose upward, creating a flat surface about 2,000 to 3,000 meters above sea level.

Later, during the Pliocene, another rise in the land formed a lower flat surface at 500 to 1,000 meters above sea level. A third stage of rising land created valleys and fjords below these flat areas. This uplift increased rainfall and lowered temperatures, allowing ice to build up and remain. As recently as 3 million years ago, during the Pliocene warm period, Greenland’s ice was limited to the highest peaks in the east and south. Since then, ice coverage has slowly expanded until about 2.7 to 2.6 million years ago, when carbon dioxide levels dropped to between 280 and 320 parts per million, and temperatures became cold enough for ice caps to connect and cover most of Greenland.

The base of the ice sheet may be warm enough due to heat from the Earth’s interior, creating liquid water beneath the ice. This water, under pressure from the ice above, can erode the ground, leaving only bedrock. However, near the top of the ice sheet, some ice slides over a frozen layer that holds ancient soil. This soil can be recovered by drilling. The oldest soil was covered by ice for about 2.7 million years, while an ice core 3 kilometers deep from the summit shows ice that is about 1,000,000 years old.

Sediment samples from the Labrador Sea show that nearly all of the southern Greenland ice melted around 400,000 years ago during Marine Isotope Stage 11. Ice cores from Camp Century in northwestern Greenland indicate that ice there melted at least once during the past 1.4 million years, during the Pleistocene, and did not return for at least 280,000 years. These findings suggest that less than 10% of today’s ice sheet remained during those times, when temperatures were less than 2.5°C (4.5°F) warmer than before the industrial era. This contradicts some climate models that assume ice would have remained solid under those conditions. Ice cores drilled from Greenland’s summit between 1989 and 1993 revealed rapid climate changes over 100,000 years, helping scientists study tipping points like changes in ocean currents.

Ice cores provide important information about past ice sheet conditions and climate. Small differences in the oxygen in water molecules from ice cores can show details about the water cycle at the time. Air bubbles trapped in ice cores also show the atmosphere’s gas and particle composition over time. When analyzed, ice cores can reveal past temperatures, rainfall, volcanic eruptions, solar activity, ocean life, soil changes, and even human impacts, such as lead production during Ancient Greece and the Roman Empire.

Recent melting

From the 1960s to the 1980s, an area in the North Atlantic that included southern Greenland was one of the few places in the world that cooled instead of warmed. This area was warmer in the 1930s and 1940s than in the decades before or after. More complete data show that warming and ice loss began in 1900, long after the Industrial Revolution started affecting global carbon dioxide levels. A strong warming trend began around 1979, matching the decline in Arctic sea ice. Between 1995 and 1999, central Greenland was 2°C (3.6°F) warmer than it was in the 1950s. From 1991 to 2004, average winter temperatures at Swiss Camp rose almost 6°C (11°F).

The 1970s were the last decade when the Greenland ice sheet grew, adding about 47 gigatonnes of ice each year. From 1980 to 1990, the ice sheet lost about 51 gigatonnes of ice each year on average. Between 1990 and 2000, the average annual loss was 41 gigatonnes per year, with 1996 being the last year the ice sheet gained more ice than it lost. By 2022, the Greenland ice sheet had lost ice for 26 years straight, and temperatures there were the highest in the past 1,000 years—about 1.5°C (2.7°F) warmer than the 20th century average.

Several factors affect how much the ice sheet grows or shrinks. These include:
• The rate of snow accumulation and melting near the center
• Melting of ice along the edges of the sheet
• Ice breaking off into the sea from glaciers along the edges

In 2001, scientists found that ice accumulation added 520 ± 26 gigatonnes per year, but ice loss from runoff, melting, and icebergs totaled about 44 gigatonnes per year.

Ice loss from the Greenland ice sheet increased in the 2000s. Between 2000 and 2010, the loss was about 187 gigatonnes per year. From 2010 to 2018, the average loss was 286 gigatonnes per year. Half of the ice sheet’s total loss from 1992 to 2018 (3,902 gigatonnes) happened during these 8 years. This ice loss contributed about 13.7 mm to sea level rise since 1972. Between 2012 and 2017, Greenland added 0.68 mm to sea level rise each year, compared to 0.07 mm per year between 1992 and 1997. Greenland’s ice loss contributed 37% of sea level rise from land ice sources (excluding ocean warming) between 2012 and 2016. These melt rates are similar to the fastest seen by the ice sheet in the past 12,000 years.

Today, Greenland loses more ice each year than Antarctica because of its location in the Arctic, where warming is more intense. Ice loss in West Antarctica has accelerated due to vulnerable glaciers like Thwaites and Pine Island. Antarctica’s contribution to sea level rise is expected to overtake Greenland’s later this century.

The retreat of outlet glaciers, which shed ice into the Arctic, is a major reason for Greenland’s ice loss. Studies show that glacier losses explain 49% to 66.8% of ice loss since the 1980s. By the 1990s, 70% of the ice sheet’s edges showed ice loss, with glaciers thinning rapidly. From 1998 to 2006, coastal glaciers thinned four times faster than in the early 1990s, losing between 1 m (3.5 ft) and 10 m (33 ft) of height per year. Landlocked glaciers did not thin as quickly.

One of the fastest thinning glaciers is Kangerlussuaq in southeast Greenland. It is 32 km (20 mi) long, 7 km (4.5 mi) wide, and about 1 km (0.5 mi) thick. Between 1993 and 1998, parts of the glacier near the coast lost 50 m (164 ft) in height. Its ice flow speed increased from 5–6 km (3.1–3.7 mi) per year in 1988–1995 to 14 km (8.7 mi) per year in 2005, the fastest known glacier speed. Kangerlussuaq’s retreat slowed by 2008 but sped up again between 2016 and 2018.

Greenland’s largest glacier, Jacobshavn Isbræ, has also changed rapidly. It loses ice from 6.5% of the ice sheet, at speeds of about 66 ft (20 m) per day. Between 1850 and 1964, it retreated 30 km (19 mi), but gained enough ice to balance losses for 35 years. After 1997, it began losing ice rapidly. By 2003, its ice flow speed had nearly doubled, and it shed 36 sq mi (94 sq km) of ice between 2001 and 2005. Its ice flow reached 148 ft (45 m) per day in 2012 but slowed later, with some mass gain between 2016 and 2019.

Petermann Glacier in northern Greenland is smaller but has lost ice quickly. It lost 33 sq mi (85 sq km) of floating ice between 2000 and 2001, and a 11 sq mi (28 sq km) iceberg broke off in 2008. In 2010, a 100 sq mi (260 sq km) iceberg calved, the largest Arctic iceberg since 1962. In 2012, another 46 sq mi (120 sq km) iceberg broke off. By 2022, Petermann had lost most of its ice.

Other glaciers, like Helheim and Nioghalvfjerdsfjorden, also show rapid ice loss. Scientists now believe ice loss is not only caused by surface melting but also by warming ocean water melting glacier fronts from below. This process, called the "Jacobshavn effect," causes glaciers to thin, reducing friction and speeding up their retreat.

Future ice loss

In 2021, the IPCC Sixth Assessment Report said that under the highest warming scenario (SSP5-8.5), melting of the Greenland ice sheet would raise global sea levels by about 13 cm (5 in). The likely range for this increase was 9–18 cm (3.5–7 in), and the very likely range was 5–23 cm (2–9 in). In a middle scenario (SSP2-4.5), sea levels would rise by about 8 cm (3 in), with a likely range of 4–13 cm (1.5–5 in) and a very likely range of 1–18 cm (0.5–7 in). In the most optimistic scenario (SSP1-2.6), which assumes the Paris Agreement goals are mostly met, sea levels would rise by about 6 cm (2.5 in), with a maximum of 15 cm (6 in). There is a small chance that the ice sheet might gain mass, lowering sea levels slightly by about 2 cm (1 in).

Some scientists, including James Hansen, have said that ice sheets might melt faster than models predict. However, even their estimates suggest that most of Greenland, which could raise sea levels by 7.4 m (24 ft) if it fully melted, would still exist by the end of the 21st century. A 2016 study by Hansen claimed that Greenland could lose enough ice to raise sea levels by about 33 cm (13 in) by 2060, with Antarctic ice loss adding twice that amount if CO₂ levels exceed 600 parts per million. This claim was controversial. A 2019 study suggested that Greenland’s ice loss could raise sea levels by up to 33 cm (13 in) by 2100 under the worst climate scenario.

Not all parts of Greenland’s ice sheet contribute equally to melting. For example, the Northeast Greenland ice stream is expected to add 1.3–1.5 cm to sea levels by 2100 under two different scenarios. Meanwhile, three large southern glaciers—Jacobshavn, Helheim, and Kangerlussuaq—are expected to add 9.1–14.9 mm under the highest warming scenario. By 2200, these glaciers and another large glacier could add 29–49 mm under the highest scenario or 19–30 mm under a lower scenario. The largest contribution to ice loss in Greenland is expected to come from the northwest and central west ice streams, including Jacobshavn. Glacier retreat, not surface melting, will likely cause most of the ice loss this century. If all coastal glaciers were to disappear, whether Greenland continues to shrink would depend on whether summer melting outweighs winter ice accumulation. This could happen as early as 2055 under the highest warming scenario.

Sea level rise from Greenland affects coasts unevenly. The southern part of the ice sheet is more vulnerable, and the weight of the ice influences Earth’s crust and rotation. This causes the U.S. East Coast to experience faster sea level rise than the global average. At the same time, Greenland itself would experience isostatic rebound, where the land rises as ice melts. A smaller ice sheet would also exert less gravitational pull on coastal waters, causing sea levels to fall near Greenland’s coasts while rising elsewhere. The opposite happened during the Little Ice Age, when increased ice weight caused flooding in Viking settlements, likely leading to their abandonment.

Greenland’s ice sheet is very large, making it slow to respond to short-term temperature changes but committed to major changes over time, as shown by past climate evidence. The Arctic, including Greenland, warms three to four times faster than the global average. During the Eemian interglacial period (130,000–115,000 years ago), Greenland’s northwest part was 130 ± 300 meters lower than today, despite global temperatures not being much higher than today. Some studies suggest that the most vulnerable parts of the ice sheet may have already passed a point of no return around 1997, meaning they will eventually disappear even if temperatures stop rising.

A 2022 study found that the climate between 2000–2019 would lead to the loss of about 3.3% of Greenland’s ice volume in the future, eventually raising sea levels by 27 cm (10.5 in), regardless of future temperature changes. If the extreme melting seen in 2012 became the new normal, Greenland’s ice loss could raise sea levels by about 78 cm (30.5 in). Another study linked paleoclimate data from 400,000 years ago to ice losses from Greenland equivalent to at least 1.4 m (4.5 ft) of sea level rise in a climate with temperatures close to 1.5 °C (2.7 °F), which are now unavoidable in the near future.

Greenland’s ice sheet could eventually melt completely if global warming reaches a certain level. Its volume was initially estimated to raise sea levels by 7.2 m (24 ft), but later estimates increased this to 7.4 m (24 ft). In 2006, scientists estimated that Greenland’s ice sheet would likely disappear if global warming reached 3.1 °C (5.6 °F), with a possible range of 1.9 °C (3.4 °F) to 5.1 °C (9.2 °F). However, this estimate was reduced in 2012, suggesting the threshold could be as low as 0.8 °C (1.4 °F) to 3.2 °C (5.8 °F), with 1.6 °C (2.9 °F) being the most likely temperature for disappearance. In 2015, NASA scientist Eric Rignot said that even the most cautious experts agree Greenland’s ice will be gone after 2 °C (3.6 °F) or 3 °C (5.4 °F) of global warming.

A 2022 review of climate tipping points suggested the threshold for Greenland’s ice sheet disappearance is most likely around 1.5 °C (2.7 °F), with an upper limit of 3 °C (5.4 °F). The worst-case threshold of 0.8 °C (1.4 °F) remained unchanged. The fastest timeline for ice sheet disintegration is 1,000 years, based on a scenario where global temperatures exceed 10 °C (18 °F) by 2500. Otherwise, ice loss would take about 10,000 years. A 2023 study using more complex models found that if the warming threshold is