Greenland ice cap
The Greenland ice cap is the largest mass of ice in the Northern Hemisphere, covering about 10 percent of the world's ice. This immense ice sheet is melting at an accelerated pace, particularly along its coastal regions, primarily due to rising summer temperatures that enhance runoff. In recent years, studies have reported that Greenland's ice loss has contributed significantly to global sea-level rise, with estimates suggesting an average loss of 270 billion tons of ice per year. The melting process has accelerated since the 1990s, with record-breaking years occurring in 2005, 2007, and beyond, leading to the formation of numerous meltwater lakes on its surface.
Scientists are concerned that continued warming could push the ice cap past a tipping point, resulting in irreversible changes and potentially raising global sea levels by up to 6 meters if the ice sheet were to shrink substantially. The dynamics of the ice melt are complex, influenced by factors such as warm ocean currents and atmospheric conditions that can enhance melting even further. Additionally, historical climate data indicate that Greenland has experienced rapid climate shifts in the past, suggesting that significant changes can occur over relatively short timescales. Understanding these processes is crucial as they have far-reaching implications for global climate patterns and coastal communities worldwide.
Greenland ice cap
The largest mass of ice in the Northern Hemisphere resides atop Greenland, which is home to 10 percent of the world’s ice. This ice has been melting at an accelerating rate, especially in coastal areas.
Background
Greenland’s ice is only a fraction of Antarctica’s, but it is melting more rapidly, in part because summers are warmer, allowing for more rapid runoff. The amount of ice lost by Greenland during 2007 was equivalent to two times all the ice in the Alps, or a layer of water more than 0.8 kilometer deep covering Washington, DC, according to Konrad Steffen, a professor of geography at the University of Colorado, who also served as the director of the Cooperative Institute for Research in Environmental Sciences. Measurements taken in 2017 showed that the ice had only continued to melt at a more rapid pace throughout the decade, with estimates, such as that given by the Arctic research program SEARCH, putting the net amount of ice lost from the sheet per year at an average of 270 billion tons. The ice sheet continued to melt through 2024.
Six Meters of Sea-Level Rise
Philippe Huybrechts, a glaciologist and ice-sheet modeler at the Free University of Brussels, has modeled the behavior of Greenland’s ice sheet throughout the late twentieth and early twenty-first century and found that, with an anticipated annual temperature increase of 8° Celsius, the will shrink to a small glaciated area far inland and the worldwide sea level will rise by 6 meters (approximately 20 feet). Erosion of the Greenland ice sheet due to prolonged warming would be irreversible.
Upon close examination of paleoclimatic proxies, scientists examining from Greenland have found that its climate can change very quickly. The island’s climate altered to a different state within one to three years at the onset of the present interglacial period, for example. Other scientists have found evidence that Greenland’s surface has been covered with pine forests within a few hundred thousand years of the present, with the ice mass a fraction of today’s size.
Ice melt in Greenland has accelerated significantly since 1990, according to a report in the Journal of Climate coauthored by Steffen. A scientific team surveyed the rate of summer melting there between 1958 and 2006, and found that the five largest melting years occurred after 1995. The year 1998 was the biggest (454 cubic kilometers), followed by 2003, 2006, 1995, and 2002. Melting in 2007 exceeded that of all previous years. According to a 2017 study in the journal Nature Climate Change, the ice sheet had contributed to over 25 percent of sea-level rise in 2014. At the same time, by 2017, researchers had begun to examine whether more surface meltwater has been retained within the ice sheet than previously thought, which could have an effect on sea-level rise projections. Scientists have also been keeping close watch on many glaciers, one of the most notable being the Jakobshavn glacier (the probable source of the iceberg that sank the Titanic), which has been accelerating toward the ocean.
Melting Acceleration
Greenland is largely an artifact of the last ice age, held in place by the (reflectivity) of its massive ice sheet. Once the ice melts, present-day climatic conditions will not allow its re-creation. Greenland’s coastal ice often melts with a boost from the sea, warm water upwelling, flowing from below. Scientists have been debating the amount of additional warming that could cause Greenland’s to cross a “tipping point,” beyond which continued melting will be inevitable. During the winters between 2003 and 2007, Greenland lost two to three times as much ice in summer melt as it regained during winter snows.
Greenland’s ice loss is accelerating irregularly year by year as well. During the 2007 melting season, with temperatures 4° to 6° Celsius higher than the previous thirty years’ average, 450 billion metric tons of ice vanished, 30 percent more than the previous year and 4 percent more than the previous record, in 2005. During years of record melting, such as 2005 and 2007, high-pressure systems over Greenland keep storms away, clearing skies, allowing the Sun to shine for extended hours. Greenland’s ice-mass loss between 2004 and 2006 was two and a half times the loss between 2002 and 2004.
By the summer of 2007, the ice cap was studded by more than one thousand shallow meltwater lakes, some as wide as 5 kilometers. Tens of millions of cubic meters of water swirl from these lakes to the base of the ice sheet within a matter of days, opening huge waterfalls where none had previously existed.
In 2012, as climate change continued to result in increased air temperatures in the summer, the US National Oceanic and Atmospheric Administration (NOAA) reported that the ice sheet experienced another summer of record-breaking melting in which the melt occurred across an even larger area than usual and began even earlier in the season than in the past. Additionally, by 2018, scientists were reporting that the increase of meltwater has subsequently led to an increase in blooms of algae, which absorb more sunlight and in turn lead to more melting.
In 2022, a study published in Nature Climate Change examined the Greenland Ice Shelf and found that it was permanently melting at a rate faster than nature could replenish. As a result, the study argued that global warming has led to an instance in which a point of no return has been passed where ice melt from the Greenland Ice Shelf will contribute to a minimum of ten inches of sea level rise regardless of corrective measures taken. Previously, the Intergovernmental Panel on Climate Change (IPCC) found that the Greenland Ice Sheet's rate of summer melting has increased since the 1990s to levels two to five times higher than pre-industrial levels. In 2024, Greenland's ice sheet lost roughly 80 gigatons of ice, contributing more than .2 millimeters to global sea level rise.
Context
Melting of the Greenland ice sheet’s western reaches increased by about 30 percent from 1979 to 2006. Ice is melting most rapidly at the edges of the ice sheet. Although Greenland’s ice sheet has been thickening at higher elevations due to increases in snowfall (warmer air holds more moisture, thus more snow), the gain is more than offset by an accelerating mass loss, partly from rapidly thinning and accelerating outlet glaciers.
Scientists using pollen records from marine sediment off southwest Greenland have deduced that much of the Greenland ice sheet has melted relatively quickly during sharp natural warming in Earth’s climate, some warming as recent as 400,000 years ago, when carbon dioxide levels were lower than they are today. During these spells, boreal coniferous forest covered much of the island. These spells of abrupt warming (abrupt, that is, in geologic time) reduced the ice sheet to about one-quarter of its present size and by themselves have raised world sea levels 4 to 6 meters.
Key Concepts
- albedo: the fraction of radiation reflected by a surface
- ice cores: cylindrical samples of ice taken from glaciers or ice caps that are used by scientists to determine atmospheric composition in the past
- Jakobshavn glacier: a major outlet glacier in Greenland whose movement toward the sea has been accelerating
- tipping point: point at which feedbacks take control and propel a climatic forcing past a point where control or mitigation is possible
- upwelling: a rising of warm water to the surface, displacing colder water and potentially melting coastal ice
Bibliography
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