Greenland ice sheet
The Greenland ice sheet first covered most of the island approximately 2.6 million years ago, marking a significant shift from earlier smaller glaciers that existed for at least 18 million years. Before this unified formation, conditions were not suitable for a single coherent ice sheet to develop across the region. Around 10 million years ago during the middle Miocene, passive continental margins experienced uplift, forming upper planation surfaces between 2000 and 3000 meters above sea level. This geological change intensified glaciation by increasing orographic precipitation and cooling surface temperatures. Later uplift during the Pliocene created lower planation surfaces ranging from 500 to 1000 meters in height. A third stage of uplift carved multiple valleys and fjords below these surfaces, allowing ice to accumulate and persist more effectively. As recently as 3 million years ago, ice cover was limited to the highest peaks in the east and south. Atmospheric carbon dioxide levels eventually dropped to between 280 and 320 parts per million around 2.7 to 2.6 million years ago. Temperatures had finally dropped sufficiently for disparate ice caps to connect and cover most of the island.
Scientists drilled long ice cores into the summit of Greenland's ice sheet between 1989 and 1993 to study past climate states. These cores revealed ice that is approximately 1,000,000 years old, providing a window into ancient atmospheric conditions. Subtle differences in oxygen isotope composition within water molecules reveal information about the historical water cycle. Air bubbles frozen inside the core offer snapshots of gas and particulate composition through time. Analysis of these records showed geologically rapid changes in climate and informed research on tipping points like the Atlantic meridional overturning circulation. Sediment samples from the Labrador Sea indicate nearly all south Greenland ice melted around 400,000 years ago during Marine Isotope Stage 11. Other ice core samples from Camp Century in northwestern Greenland show melting occurred at least once during the Pleistocene over the past 1.4 million years. During those periods, less than 10% of the current ice sheet volume remained when temperatures were less than 2 degrees warmer than preindustrial conditions. The oldest soil continuously covered by ice dates back around 2.7 million years near the summit.
The 1970s marked the last decade when the Greenland ice sheet grew, gaining about 47 gigatonnes per year. From 1980 to 1990, average annual mass loss reached approximately 51 gigatons per year. The period between 1990 and 2000 showed an average annual loss of 41 gigatons, with 1996 being the final year the sheet saw net mass gain. As of 2022, the ice sheet had been losing ice for 26 consecutive years. Temperatures there have been the highest in the entire past millennium, roughly 3 degrees warmer than the 20th century average. Annual ice losses accelerated in the 2000s, reaching approximately 187 gigatons per year during 2000, 2010. An average mass loss of 286 gigatons occurred annually between 2010 and 2018. Half of the observed net loss of 3,902 gigatons happened during those eight years alone. Between 2012 and 2017, the sheet contributed 0.68 millimeters per year to sea level rise compared to 0.07 millimeters per year from 1992 to 1997. Greenland's net contribution for the 2012, 2016 period equaled 37% of sea level rise from land ice sources excluding thermal expansion.
Kangerlussuaq Glacier in southeast Greenland is over 50 kilometers long and around 4 kilometers wide, making it the third largest glacier in the region. Between 1993 and 1998, parts of this glacier within 10 kilometers of the coast lost 10 meters in height. Its observed ice flow speed increased from 4 kilometers per year in 1988, 1995 to 14 kilometers per year in 2005. Jacobshavn Isbræ in west Greenland historically sheds ice from 6.5% of the ice sheet at speeds of approximately 20 meters per day. It retreated around 12 kilometers between 1850 and 1964 but remained balanced for the next 35 years before switching to rapid mass loss after 1997. By 2003, average annual ice flow speed had almost doubled since 1997 as the ice tongue disintegrated. Petermann Glacier in northern Greenland lost a floating iceberg measuring 250 square kilometers in August 2010. This became the largest Arctic iceberg since 1962 and amounted to a quarter of the shelf's size. In July 2012, another major iceberg broke off measuring 100 square kilometers, twice the area of Manhattan.
On the 22nd of December 1991, an automatic weather station near the topographic summit recorded a temperature of -57 degrees Celsius, the lowest ever recorded in the Northern Hemisphere. The record went unnoticed for more than 28 years until finally recognized in 2020. High albedo allows the bright white surface to reflect sunlight effectively, keeping temperatures low. As temperatures increase, darker melt ponds form on the surface, reducing albedo and accelerating warming. Mats of algae grow on the ice sheet surface and are darker than the surrounding ice, absorbing more thermal radiation. Regions covered in dust, soot, and living microbes grew by 12% between 2000 and 2012. By 2020, research demonstrated that algae presence was already increasing annual melting by 10, 13%. Thin water-rich clouds were most prominent during the massive melting event of July 2012. These clouds interfere with meltwater refreezing in the firn layer at night, potentially increasing total runoff by over 30%. The snow line moves around every summer, exposing darker ice below it to substantially greater melt when it shifts away from areas it previously covered.
Greenland's melt resulted in 300 cubic kilometers of fresh meltwater entering the seas annually as early as 1993. This volume equaled 0.7% of freshwater entering oceans from all world rivers combined. Meltwater contains iron, about half of which is bioavailable as a nutrient for phytoplankton. Approximately 40% of total primary production in the Labrador Sea had been attributed to nutrients from this meltwater. Increased discharge from Greenland connects to the cold blob visible on NASA global mean temperatures for 2015. A 2016 study attempted to improve forecasts of future Atlantic meridional overturning circulation changes by incorporating better simulation of Greenland trends into eight state-of-the-art climate models. That research found that by 2090, 2100, AMOC would weaken by around 18% under Representative Concentration Pathway 4.5. Under RCP 8.5, which assumes continually increasing emissions, weakening could reach 37% with a range between 15% and 65%. If extended past 2100, average decline by 2290, 2300 reaches 74%, with a 44% likelihood of outright collapse.
The IPCC Sixth Assessment Report estimated that under SSP5-8.5, Greenland ice sheet melt would add around 0.4 meters to global sea levels by 2100. The moderate SSP2-4.5 scenario adds 0.2 meters with a likely range of 0.1 to 0.3 meters. The optimistic SSP1-2.6 scenario adds around 0.1 meters and no more than 0.2 meters. Some scientists led by James Hansen claimed ice loss could add around 0.5 meters by 2060 if carbon dioxide concentration exceeded 600 parts per million. A 2019 research paper from different scientists claimed a maximum of 0.8 meters by 2100 under the worst-case climate change scenario. On its own, the Northeast Greenland ice stream would contribute 1.3 to 1.5 centimeters by 2100 under RCP 4.5 and RCP 8.5 respectively. The three largest glaciers Jacobshavn, Helheim, and Kangerlussuaq are expected to add 9.1 to 14.9 millimeters under RCP 8.5 alone. By 2200, these four large glaciers could add 29 to 49 millimeters under RCP 8.5 or 19 to 30 millimeters under RCP 4.5. If warming passes 1.5 degrees, approximately 0.7 meters of sea level rise becomes inevitable.
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Common questions
When did the Greenland ice sheet first cover most of the island?
The Greenland ice sheet first covered most of the island approximately 2.6 million years ago. This formation occurred after atmospheric carbon dioxide levels dropped to between 280 and 320 parts per million around 2.7 to 2.6 million years ago.
What are the oldest continuously ice-covered soil dates for the Greenland ice sheet summit?
The oldest soil continuously covered by ice near the summit of the Greenland ice sheet dates back around 2.7 million years. Scientists drilled long ice cores into this area between 1989 and 1993 to study these ancient conditions.
How much mass has the Greenland ice sheet lost annually during recent decades?
Average annual mass loss reached 286 gigatons between 2010 and 2018, with half of the observed net loss of 3,902 gigatons occurring during those eight years alone. As of 2022, the Greenland ice sheet had been losing ice for 26 consecutive years.
Which glacier in southeast Greenland is over 50 kilometers long and how fast does it flow?
Kangerlussuaq Glacier in southeast Greenland is over 50 kilometers long and flows at speeds that increased from 4 kilometers per year between 1988 and 1995 to 14 kilometers per year in 2005. This makes it the third largest glacier in the region.
What temperature record was set on the topographic summit of the Greenland ice sheet in December 1991?
An automatic weather station recorded a temperature of -57 degrees Celsius on the 22nd of December 1991 near the topographic summit. This remains the lowest ever recorded temperature in the Northern Hemisphere.