Arctic sea ice decline

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Decline in arctic sea ice extent (area) from 1979 to 2022
Decline in arctic sea ice volume from 1979 to 2022

Arctic sea ice decline has occurred in recent decades and is an effect of climate change; sea ice in the Arctic Ocean has melted more than it refreezes in the winter. Global warming, caused by greenhouse gas forcing is responsible for the decline in Arctic sea ice. Implications of arctic sea ice decline may include: Ice-free summer, amplified arctic warming, polar vortex disruption, atmospheric chemistry changes, atmospheric regime changes, changes to plant, animal, and microbial life; changed shipping options and other impacts on humans.

Sea ice in the arctic is currently in decline in area, extent, and volume, and has been accelerating during the early twenty‐first century, with a decline rate of −4.7% per decade (it has declined over 50% since the first satellite records).[1][2][3] It is also thought that summertime sea ice will cease to exist sometime during the 21st century.[4] This sea ice loss is one of the main drivers of surface-based Arctic amplification. Sea ice area means the total area covered by ice, whereas sea ice extent is the area of ocean with at least 15% sea ice, while the volume is the total amount of ice in the Arctic.[5]

The region is at its warmest in at least 4,000 years[6] and the Arctic-wide melt season has lengthened at a rate of five days per decade (from 1979 to 2013), dominated by a later autumn freeze-up.[7] Sea ice changes are a mechanism for polar amplification.[8] The IPCC Sixth Assessment Report (2021) stated that Arctic sea ice area will likely drop below 1 million km2 in at least some Septembers before 2050.[9]

In September 2020, the US National Snow and Ice Data Center reported that the Arctic sea ice in 2020 had melted to an area of 3.74 million km2, its second-smallest area since records began in 1979.[10]


September 2, 2012, the record lowest minimum ever observed in the satellite record
September 2, 2012. Two weeks later, the record lowest minimum occurred: 3,410,000 square kilometres (1,320,000 sq mi).
January 1, 2013, to September 10, 2016, when the sea ice reached its annual minimum extent
Arctic sea ice grows and extends through the winter. On March 7, 2017, Arctic sea ice reached its record lowest maximum.
Older and thicker ice changes from 1984 to 2016 (video)

The Arctic Ocean is the mass of water positioned approximately above latitude 65° N. Arctic Sea Ice refers to the area of the Arctic Ocean covered by ice. The Arctic sea ice minimum is the day in a given year when Arctic sea ice reaches its smallest extent, occurring at the end of the summer melting season, normally during September. Arctic Sea ice maximum is the day of a year when Arctic sea ice reaches its largest extent near the end of the Arctic cold season, normally during March.[11] Typical data visualizations for Arctic sea ice include average monthly measurements or graphs for the annual minimum or maximum extent, as shown in the adjacent images.

Sea ice extent is defined as the area with at least 15% of sea ice cover; it is more often used as a metric than simple total sea ice area. This metric is used to address uncertainty in distinguishing open sea water from melted water on top of solid ice, which satellite detection methods have difficulty differentiating. This is primarily an issue in summer months.

Sea ice and climate feedback[edit]

Arctic sea ice maintains the cool temperature of the polar regions and it has an important albedo effect on the climate. Arctic sea ice melts in the summer, and more solar energy is being absorbed by the ocean. The sea ice melting is resulting in the oceans absorbing and heating up the Arctic. The decline in sea ice has the potential to speed up global warming and climate change.[11][12]


A 2007 study found the decline to be "faster than forecasted" by model simulations.[13] A 2011 study suggested that it could be reconciled by internal variability enhancing the greenhouse gas-forced sea ice decline over the last few decades.[14] A 2012 study, with a newer set of simulations, also projected rates of retreat that were somewhat less than that actually observed.[15]

An animation of the annual Arctic sea ice minimum with a graph overlay showing the area of the minimum sea ice in millions of square kilometres

Satellite era[edit]

2018 sea ice extent visualization

Observation with satellites shows that Arctic sea ice area, extent, and volume have been in decline for a few decades.[16] The amount of multi-year sea ice in the Arctic has declined considerably in recent decades. In 1988, ice that was at least 4 years old accounted for 26% of the Arctic's sea ice. By 2013, ice that age was only 7% of all Arctic sea ice.[17]

Scientists recently measured sixteen-foot (five-meter) wave heights during a storm in the Beaufort Sea in mid-August until late October 2012. This is a new phenomenon for the region, since a permanent sea ice cover normally prevents wave formation. Wave action breaks up sea ice, and thus could become a feedback mechanism, driving sea ice decline.[18]

For January 2016, the satellite-based data showed the lowest overall Arctic sea ice extent of any January since records began in 1979. Bob Henson from Wunderground noted:

Hand in hand with the skimpy ice cover, temperatures across the Arctic have been extraordinarily warm for midwinter. Just before New Year’s, a slug of mild air pushed temperatures above freezing to within 200 miles of the North Pole. That warm pulse quickly dissipated, but it was followed by a series of intense North Atlantic cyclones that sent very mild air poleward, in tandem with a strongly negative Arctic oscillation during the first three weeks of the month.[19]

January 2016's remarkable phase transition of Arctic oscillation was driven by a rapid tropospheric warming in the Arctic, a pattern that appears to have increased surpassing the so-called stratospheric sudden warming.[20] The previous record of the lowest extent of the Arctic Ocean covered by ice in 2012 saw a low of 1.31 million square miles (3.387 million square kilometers). This replaced the previous record set on September 18, 2007, at 1.61 million square miles (4.16 million square kilometers). The minimum extent on 18th Sept 2019 was 1.60 million square miles (4.153 million square kilometers). [21]

A 2018 study of the thickness of sea ice found a decrease of 66% or 2.0 m over the last six decades and a shift from permanent ice to largely seasonal ice cover.[22]

Impacts on the physical environment[edit]

Map illustrating various Arctic shipping routes

Ice-free summer[edit]

The dark ocean surface reflects only 6 percent of incoming solar radiation; instead sea ice reflects 50 to 70 percent.[23]
As ice melts, the liquid water collects in depressions on the surface and deepens them, forming these melt ponds in the Arctic. These fresh water ponds are separated from the salty sea below and around it, until breaks in the ice merge the two.

An "ice-free" Arctic Ocean, sometimes referred to as a "Blue Ocean Event",[24] is often defined as "having less than 1 million square kilometers of sea ice", because it is very difficult to melt the thick ice around the Canadian Arctic Archipelago.[25][26][27] The IPCC AR5 defines "nearly ice-free conditions" as a sea ice extent of less than 106 km2 for at least five consecutive years.[28]

The IPCC Sixth Assessment Report (2021) stated that Arctic sea ice area will likely drop below 1 million km2 in at least some Septembers before 2050.[9] Also, a practically ice-free Arctic in September is likely before the year 2050.[9]

Many scientists have attempted to estimate when the Arctic will be "ice-free", among them Peter Wadhams who in 2014 predicted that by 2020 "summer sea ice [will] disappear,"[29][30] Wadhams and several others have noted that climate model predictions have been overly conservative regarding sea ice decline.[13][31] A 2013 paper suggested that models commonly underestimate the solar radiation absorption characteristics of wildfire soot.[32] In 2007, Professor Wieslaw Maslowski from the Naval Postgraduate School, California, predicted removal of summer ice by 2013;[33] subsequently, in 2013, Maslowski predicted 2016 ±3 years.[34] A 2006 paper predicted "near ice-free September conditions by 2040".[35] Overland and Wang (2013) investigated three different ways of predicting future sea ice levels.[36] The IPCC AR5 (for at least one scenario) estimates an ice-free summer might occur around 2050.[28] The IPCC AR6 report instead assesses that there is "high confidence" that the Arctic Ocean will likely become practically ice-free in September before the year 2050 under all SSP scenarios.[37] The Third U.S. National Climate Assessment (NCA), released May 6, 2014, also reports that the Arctic Ocean is expected to be ice free in summer before mid-century. Models that best match historical trends project a nearly ice-free Arctic in the summer by the 2030s.[38][39] However, these models do tend to underestimate the rate of sea ice loss since 2007. Based on the outcomes of several different models, Overland and Wang (2013) put the early limit for a sea ice free summer Arctic near 2040.[36] Professor James Anderson of Harvard University envisions the Arctic Ice gone by the early 2020s. "The chance that there will be any permanent ice left in the Arctic after 2022 is essentially zero," he said in June 2019.[40]

Monthly averages 1979–2021. Data source via the Polar Science Center (University of Washington).

No tipping point[edit]

The IPCC Sixth Assessment Report in 2021 said with high confidence that there is no hysteresis and no tipping point in the loss of Arctic summer sea ice.[37] This can be explained by the increased influence of stabilizing feedback compared to the ice albedo feedback. Specifically, thinner sea ice leads to increased heat loss in the winter, creating a negative feedback loop. This counteracts the positive ice albedo feedback.

Amplified Arctic warming[edit]

Dark, open water left behind as sea ice melts absorbs more heat than ice-covered water, leading to physical implications that include the ice–albedo feedback or warmer sea surface temperatures which increase ocean heat content.[41] This also increases pressure and decreases wind speeds. These feedback effects are stronger in the lower atmosphere.[42] As Peter Wadhams, a polar researcher writes "once summer ice yields to open water, the albedo ... drops from 0.6 to 0.1, which will further accelerate warming of the Arctic and of the whole planet."[43] The Arctic is heating approximately twice as fast as the global average, according to Rutgers University climate scientist Jennifer Francis.[44] Economic implications of ice-free summers and the decline in Arctic ice volumes include a greater number of journeys across the Arctic Ocean Shipping lanes during the year. This number has grown from 0 in 1979 to 400–500 along the Bering strait and >40 along the Northern Sea Route in 2013.[45] Arctic amplified warming is observed as stronger in lower atmospheric areas because the expanding process of warmer air increases pressure levels which decreases poleward geopotential height gradients. These gradients are the reason that cause west to east winds through the thermal wind relationship, declining speeds are usually found south of the areas with geopotential increases. This relationship has been documented through observation evidence and model responses to sea ice loss according to the 2017 Wiley Periodicals Article, Amplified Arctic warming and mid latitude weather: new perspectives on emerging connections.[46]

Polar vortex disruption[edit]

The polar vortex is a whirlwind of especially cold, dense air forming near the poles that is contained by the jet stream, a belt of fast-flowing winds that serves as a boundary between cold polar air and the warmer air of other hemispheres. Because the power of the polar vortex and jet stream is derived partly from the temperature contrast between cold polar air and warmer tropical air, it is at risk of becoming severely diminished as this contrast is eroded by the effects of melting sea ice.[44] According to the Journal of the Atmospheric Sciences "there [has been] a significant change in the vortex mean state over the twenty-first century, resulting in a weaker, more disturbed vortex."[47] As the vortex becomes weaker, it is more likely to allow cold arctic air to escape from the confines of the jet stream and spill over into other hemispheres.[44] This disruption has already begun to affect global temperatures. In a 2017 study conducted by climatologist Dr. Judah Cohen and several of his research associates, Cohen wrote that "[the] shift in polar vortex states can account for most of the recent winter cooling trends over Eurasian midlatitudes".[48] A 2021 study found that a stratospheric polar vortex disruption is linked with extreme cold winter weather across parts of Asia and North America, including the February 2021 North American cold wave.[49][50]

Atmospheric chemistry[edit]

Cracks in sea ice can expose the food chain to greater amounts of atmospheric mercury.[51][52]

A 2015 study concluded that Arctic sea ice decline accelerates methane emissions from the Arctic tundra. One of the study researchers noted, "The expectation is that with further sea ice decline, temperatures in the Arctic will continue to rise, and so will methane emissions from northern wetlands."[53]

Atmospheric regime[edit]

Influence of Arctic sea ice on European summer precipitation

A link has been proposed between reduced Barents-Kara sea ice and cold winter extremes over northern continents.[54] Model simulation suggest diminished Arctic sea ice may have been a contributing driver of recent wet summers over northern Europe, because of a weakened jet stream, which dives further south.[55] Extreme summer weather in northern mid-latitudes has been linked to a vanishing cryosphere.[56] Evidence suggest that the continued loss of Arctic sea-ice and snow cover may influence weather at lower latitudes. Correlations have been identified between high-latitude cryosphere changes, hemispheric wind patterns and mid-latitude extreme weather events for the Northern Hemisphere.[57] A study from 2004, connected the disappearing sea ice with a reduction of available water in the American west.[58]

Based on the effects of Arctic amplification (warming) and ice loss, a study in 2015 concluded that highly amplified jet-stream patterns are occurring more frequently in the past two decades, and that such patterns can not be tied to certain seasons. Additionally, it was found that these jet-stream patterns often lead to persistent weather patterns that result in extreme weather events. Hence, continued heat-trapping emissions favour increased formation of extreme events caused by prolonged weather conditions.[59]

In 2018, climate scientist Michael E. Mann explained that the west Antarctic ice sheet may lose twice as much ice by the end of the century as previously thought, which also doubles the projected rise in sea level from three feet to more than six feet.[60]

This animation shows the difference in the area, volume and depth of the average September Arctic sea ice between 1979 and 2013.

Impacts on humans[edit]

The decline of arctic sea ice will provide humans with access to previously remote coastal zones. As a result, this will lead to an undesirable effect on terrestrial ecosystems and put marine species at risk.[61]

In the years leading up to 2015, Greenland's ice cover decreased to "a rotten ice regime", with months of solid ice decreasing from 9 per year to 2–3, and with thickness decreasing from 6–10 feet to 7 inches by 2004.[62] The decline of solid land ice to rotten ice strongly disrupts travel and subsistence hunting for the local Inuit, as well as travel and habitat for sea mammals. The Inuit have been forced out of traditional hunting locations and styles to various degrees, and alcoholism and suicides increased due to the massive and rapid lifestyle shift.[62]


Melting Arctic sea ice is likely to increase traffic through the Arctic Ocean.[63][64] An early study by James Hansen and colleagues suggested in 1981 that a warming of 5 to 10 °C, which they expected as the range of Arctic temperature change corresponding to doubled CO2 concentrations, could open the Northwest Passage.[65] A 2016 study concludes that Arctic warming and sea ice decline will lead to "remarkable shifts in trade flows between Asia and Europe, diversion of trade within Europe, heavy shipping traffic in the Arctic and a substantial drop in Suez traffic. Projected shifts in trade also imply substantial pressure on an already threatened Arctic ecosystem."[66] In August 2017, the first ship traversed the Northern Sea Route without the use of ice-breakers.[67] Also in 2017, the Finnish icebreaker MSV Nordica set a record for the earliest crossing of the Northwest Passage.[68] According to the New York Times, this forebodes more shipping through the Arctic, as the sea ice melts and makes shipping easier.[67] A 2016 report by the Copenhagen Business School found that large-scale trans-Arctic shipping will become economically viable by 2040.[69][67]

Impacts on plants, animals, and microbial life[edit]

Sea ice decline has been linked to boreal forest decline in North America and is assumed to culminate with an intensifying wildfire regime in this region.[70] The annual net primary production of the Eastern Bering Sea was enhanced by 40–50% through phytoplankton blooms during warm years of early sea ice retreat.[71]

Polar bears are turning to alternative food sources because Arctic sea ice melts earlier and freezes later each year. As a result, they have less time to hunt their historically preferred prey of seal pups, and must spend more time on land and hunt other animals.[72] As a result, the diet is less nutritional, which leads to reduced body size and reproduction, thus indicating population decline in polar bears.[73] The arctic refuge is where polar bears main habitat is to den and the melting arctic sea ice is causing a loss of species. There are only about 900 bears in the Arctic refuge national conservation area.[74]

As arctic ice decays, microorganisms produce substances with various effects on melting and stability. Certain types of bacteria in rotten ice pores produce polymer-like substances, which may influence the physical properties of the ice. A team from the University of Washington studying this phenomenon hypothesizes that the polymers may provide a stabilizing effect to the ice.[75] However, other scientists have found algae and other microorganisms help create a substance, cryoconite, or create other pigments that increase rotting and increase the growth of the microorganisms.[76][77]

See also[edit]


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