Arctic sea ice extent and area have declined every decade since the start of start of satellite observations in 1979: Greenland ice sheet had experienced a "massive melting event" in 2012, which reoccurred in 2019 and 2021; Satellite image of the extremely anomalous 2020 Siberian heatwave; Permafrost thaw is leading to severe
erosion, like in this coastal location in
Alaska
Due to climate change in the Arctic, this polar region is expected to become "profoundly different" by 2050.[1]: 2321 The speed of change is "among the highest in the world",[1]: 2321 with the rate of warming being 3-4 times faster than the global average.[2][3][4][5] This warming has already resulted in the profound
Arctic sea ice decline, the accelerating melting of the
Greenland ice sheet and the thawing of the
permafrost landscape.[1]: 2321 [6] These ongoing transformations are expected to be irreversible for centuries or even millennia.[1]: 2321
Natural life in the Arctic is affected greatly. As the
tundra warms, its soil becomes more hospitable to
earthworms and larger plants,[7] and the
boreal forests spread to the north - yet this also makes the landscape more prone to
wildfires, which take longer to recover from than in the other regions.
Beavers also take advantage of this warming to colonize the Arctic rivers, and their
dams contributing to
methane emissions due to the increase in stagnant waters.[8] The
Arctic Ocean has experienced a large increase in the
marine primary production as warmer waters and less shade from sea ice benefit
phytoplankton.[1]: 2326 [9] At the same time, it is already less alkaline than the rest of the global ocean, so
ocean acidification caused by the increasing CO2 concentrations is more severe, threatening some forms of
zooplankton such as
pteropods.[1]: 2328
The Arctic Ocean is expected to see its first ice-free events in the near future - most likely before 2050, and potentially in the late 2020s or early 2030s.[10] This would have no precedent in the last 700,000 years.[11][12] Some sea ice regrows every Arctic winter, but such events are expected to occur more and more frequently as the warming increases. This has great implications for the
fauna species which are dependent on sea ice, such as
polar bears. For humans, trade routes across the ocean will become more convenient. Yet, multiple countries have
infrastructure in the Arctic which is worth billions of dollars, and it is threatened with collapse as the underlying permafrost thaws. The Arctic's indigenous people have a long relationship with its icy conditions, and face the loss of their cultural heritage.
Further, there are numerous implications which go beyond the Arctic region. Sea ice loss not only enhances warming in the Arctic but also adds to global temperature increase through the
ice-albedo feedback. Permafrost thaw results in emissions of CO2 and methane that are comparable to those of major countries. Greenland melting is a significant contributor to global
sea level rise. If the warming exceeds - or thereabouts, there is a significant risk of the entire ice sheet being lost over an estimated 10,000 years, adding up to global sea levels. Warming in the Arctic may affect the stability of the
jet stream, and thus the extreme weather events in
midlatitude regions, but there is only "low confidence" in that hypothesis.
Impacts on the physical environment
Warming
The period of 1995–2005 was the warmest decade in the Arctic since at least the 17th century, with temperatures 2 °C (3.6 °F) above the 1951–1990 average.[13] Alaska and western Canada's temperature rose by 3 to 4 °C (5.40 to 7.20 °F) during that period.[14] 2013 research has shown that temperatures in the region haven't been as high as they currently are since at least 44,000 years ago and perhaps as long as 120,000 years ago.[15][16] Since 2013, Arctic annual mean surface air temperature (SAT) has been at least 1 °C (1.8 °F) warmer than the 1981-2010 mean.
In 2016, there were extreme anomalies from January to February with the temperature in the Arctic being estimated to be between 4–5.8 °C (7.2–10.4 °F) more than it was between 1981 and 2010.[17] In 2020, mean SAT was 1.9 °C (3.4 °F) warmer than the 1981–2010 average.[18] On 20 June 2020, for the first time, a temperature measurement was made inside the Arctic Circle of 38 °C, more than 100 °F. This kind of weather was expected in the region only by 2100. In March, April and May the average temperature in the Arctic was 10 °C (18.0 °F) higher than normal.[19][20] This heat wave, without human – induced warming, could happen only one time in 80,000 years, according to an attribution study published in July 2020. It is the strongest link of a weather event to anthropogenic climate change that had been ever found, for now.[21]
Snow– and ice–albedo feedback have a substantial effect on regional temperatures. In particular, the presence of ice cover and
sea ice makes the
North Pole and the
South Pole colder than they would have been without it.[22] Consequently, recent
Arctic sea ice decline is one of the primary factors behind the Arctic warming nearly four times faster than the global average since 1979 (the year when continuous satellite readings of the Arctic sea ice began), in a phenomenon known as
Arctic amplification.[23]
Modelling studies show that strong Arctic amplification only occurs during the months when significant sea ice loss occurs, and that it largely disappears when the simulated ice cover is held fixed.[24] Conversely, the high stability of ice cover in Antarctica, where the thickness of the
East Antarctic ice sheet allows it to rise nearly 4 km above the sea level, means that this continent has experienced very little net warming over the past seven decades, most of which was concentrated in West Antarctica.[25][26][27] Ice loss in the Antarctic and its contribution to
sea level rise is instead driven overwhelmingly by the warming of the
Southern Ocean, which had absorbed 35–43% of the total heat taken up by all oceans between 1970 and 2017.[28]
Ice–albedo feedback also has a smaller, but still notable effect on the global temperatures.
Arctic sea ice decline between 1979 and 2011 is estimated to have been responsible for 0.21 watts per square meter (W/m2) of
radiative forcing, which is equivalent to a quarter of radiative forcing from
CO2[29] increases over the same period. When compared to cumulative increases in
greenhouse gas radiative forcing since the start of the
Industrial Revolution, it is equivalent to the estimated 2019 radiative forcing from
nitrous oxide (0.21 W/m2), nearly half of 2019 radiative forcing from
methane (0.54 W/m2) and 10% of the cumulative CO2 increase (2.16 W/m2).[30] Between 1992 and 2015, this effect was partly offset by the growth in
sea ice cover around
Antarctica, which produced cooling of about 0.06 W/m2 per decade. However, Antarctic sea ice had also begun to decline afterwards, and the combined role of changes in ice cover between 1992 and 2018 is equivalent to 10% of all the anthropogenic
greenhouse gas emissions.[31]
The Arctic was historically described as warming twice as fast as the global average,[33] but this estimate was based on older observations which missed the more recent acceleration. By 2021, enough data was available to show that the Arctic had warmed three times as fast as the globe - 3.1°C between 1971 and 2019, as opposed to the global warming of 1°C over the same period.[34] Moreover, this estimate defines the Arctic as everything above
60th parallel north, or a full third of the Northern Hemisphere: in 2021–2022, it was found that since 1979, the warming within the
Arctic Circle itself (above the 66th parallel) has been nearly four times faster than the global average.[35][36] Within the Arctic Circle itself, even greater Arctic amplification occurs in the
Barents Sea area, with hotspots around
West Spitsbergen Current: weather stations located on its path record decadal warming up to seven times faster than the global average.[37][38] This has fuelled concerns that unlike the rest of the Arctic sea ice, ice cover in the Barents Sea may permanently disappear even around 1.5 degrees of global warming.[39][40]
The acceleration of Arctic amplification has not been linear: a 2022 analysis found that it occurred in two sharp steps, with the former around 1986, and the latter after 2000.[41] The first acceleration is attributed to the increase in anthropogenic
radiative forcing in the region, which is in turn likely connected to the reductions in
stratospheric sulfur aerosols pollution in Europe in the 1980s in order to combat
acid rain. Since sulphate aerosols have a cooling effect, their absence is likely to have increased Arctic temperatures by up to 0.5 degrees Celsius.[42][43] The second acceleration has no known cause,[34] which is why it did not show up in any climate models. It is likely to be an example of multi-decadal natural variability, like the suggested link between Arctic temperatures and
Atlantic Multi-decadal Oscillation (AMO),[44] in which case it can be expected to reverse in the future. However, even the first increase in Arctic amplification was only accurately simulated by a fraction of the current
CMIP6 models.[41]
Precipitation
An observed impact of climate change is aa strong increase in the number of lightnings in the Arctic. Lightnings increase the risk for wildfires.[45] Some research suggests that globally, a warming greater than 1.5 °C (2.7 °F) over the preindustrial level could change the type of precipitation in the Arctic from snow to rain in summer and autumn.[46]
Sea ice in the
Arctic region has declined in recent decades in area and volume due to
climate change. It has been melting more in summer than it refreezes in winter.
Global warming, caused by
greenhouse gas forcing is responsible for the decline in Arctic sea ice. The decline of sea ice in the Arctic 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).[48][49][50] It is also thought that summertime sea ice will cease to exist sometime during the 21st century.[51]
The region is at its warmest in at least 4,000 years[52] 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.[53] 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.[54] In September 2020, the US
National Snow and Ice Data Center reported that the Arctic sea ice in 2020 had melted to an extent of 3.74 million km2, its second-smallest extent since records began in 1979.[55] Earth lost 28 trillion tonnes of ice between 1994 and 2017, with Arctic sea ice accounting for 7.6 trillion tonnes of this loss. The rate of ice loss has risen by 57% since the 1990s.[56]
Greenland has had major
glaciers and
ice caps for at least 18 million years,[57] but a single ice sheet first covered most of the island some 2.6 million years ago.[58] Since then, it has both grown[59][60] and contracted significantly.[61][62][63] The oldest known ice on Greenland is about 1 million years old.[64] Due to anthropogenic
greenhouse gas emissions, the ice sheet is now the warmest it has been in the past 1000 years,[65] and is losing ice at the fastest rate in at least the past 12,000 years.[66]
Every summer, parts of the surface melt and
ice cliffs calve into the sea. Normally the ice sheet would be replenished by winter snowfall,[67] but due to
global warming the ice sheet is melting two to five times faster than before 1850,[68] and snowfall has not kept up since 1996.[69] If the
Paris Agreement goal of staying below 2 °C (3.6 °F) is achieved, melting of Greenland ice alone would still add around 6 cm (2+1⁄2 in) to global
sea level rise by the end of the century. If there are no reductions in emissions, melting would add around 13 cm (5 in) by 2100,[70]: 1302 with a worst-case of about 33 cm (13 in).[71] For comparison, melting has so far contributed 1.4 cm (1⁄2 in) since 1972,[72] while sea level rise from all sources was 15–25 cm (6–10 in)) between 1901 and 2018.[73]: 5
If all 2,900,000 cubic kilometres (696,000 cu mi) of the ice sheet were to melt, it would increase global sea levels by ~7.4 m (24 ft).[74] Global warming between 1.7 °C (3.1 °F) and 2.3 °C (4.1 °F) would likely make this melting inevitable.[75] However, 1.5 °C (2.7 °F) would still cause ice loss equivalent to 1.4 m (4+1⁄2 ft) of sea level rise,[76] and more ice will be lost if the temperatures exceed that level before declining.[75] If global temperatures continue to rise, the ice sheet will likely disappear within 10,000 years.[77][78] At very high warming, its future lifetime goes down to around 1,000 years.[71]
Biological environment
Impacts on Arctic flora
Climate change is expected to have a strong effect on the Arctic's flora, some of which is already being seen.[79] NASA and NOAA have continuously monitored Arctic vegetation with satellite instruments such as
Moderate Resolution Imaging Spectroradiometer (MODIS) and
Advanced very-high-resolution radiometer (AVHRR).[80] Their data allows scientists to calculate so-called "Arctic greening" and "Arctic browning".[81] From 1985 to 2016, greening has occurred in 37.3% of all sites sampled in the tundra, whereas browning was observed only in 4.7% of the sites - typically the ones that were still experiencing cooling and drying, as opposed to warming and wettening for the rest.[82]
This expansion of vegetation in the Arctic is not equivalent across types of vegetation. A major trend has been from
shrub-type plants taking over areas previously dominated by moss and lichens. This change contributes to the consideration that the tundra biome is currently experiencing the most rapid change of any terrestrial biomes on the planet.[83][84] The direct impact on mosses and lichens is unclear as there exist very few studies at species level, but climate change is more likely to cause increased fluctuation and more frequent extreme events.[85] While shrubs may increase in range and biomass, warming may also cause a decline in
cushion plants such as moss campion, and since
cushion plants act as facilitator species across
trophic levels and fill important ecological niches in several environments, this could cause cascading effects in these ecosystems that could severely affect the way in which they function and are structured.[86]
The expansion of these shrubs can also have strong effects on other important ecological dynamics, such as the
albedo effect.[87] These shrubs change the winter surface of the tundra from undisturbed, uniform snow to mixed surface with protruding branches disrupting the snow cover,[88] this type of snow cover has a lower albedo effect, with reductions of up to 55%, which contributes to a positive feedback loop on regional and global climate warming.[88] This reduction of the albedo effect means that more radiation is absorbed by plants, and thus, surface temperatures increase, which could disrupt current surface-atmosphere energy exchanges and affect thermal regimes of permafrost.[88] Carbon cycling is also being affected by these changes in vegetation, as parts of the tundra increase their shrub cover, they behave more like boreal forests in terms of carbon cycling.[89] This is speeding up the carbon cycle, as warmer temperatures lead to increased permafrost thawing and carbon release, but also carbon capturing from plants that have increased growth.[89] It is not certain whether this balance will go in one direction or the other, but studies have found that it is more likely that this will eventually lead to increased CO2 in the atmosphere.[89]
However, boreal forests, particularly those in North America, showed a different response to warming. Many boreal forests greened, but the trend was not as strong as it was for tundra of the circumpolar Arctic, mostly characterized by shrub expansion and increased growth.[90] In North America, some boreal forests actually experienced browning over the study period. Droughts, increased forest fire activity, animal behavior, industrial pollution, and a number of other factors may have contributed to browning.[81]
Impacts on terrestrial fauna
Arctic warming negatively affects the foraging and breeding ecology of native Arctic mammals, such as
Arctic foxes or
Arctic reindeer.[91] In July 2019, 200
Svalbard reindeer were found starved to death apparently due to low precipitation related to climate change.[92] This was only one episode in the long-term decline of the species.[1]: 2327 United States Geological Survey research suggests that the shrinkage of Arctic sea ice would eventually extirpate polar bears from
Alaska, but leave some of their
habitat in the
Canadian Arctic Archipelago and areas off the northern Greenland coast.[93][94]
As the pure
Arctic climate is gradually replaced by the
subarctic climate, animals adapted to those conditions spread to the north.[1]: 2325 For instance,
beavers have been actively colonizing Arctic regions, and as they create
dams, they flood areas which used to be permafrost, contributing to its thaw and methane emissions from it.[8] These colonizing species can outright replace native species, and they may also interbreed with their southern relations, like in the case of the
Grizzly–polar bear hybrid. This usually has the effect of reducing the
genetic diversity of the
genus.
Infectious diseases, such as
brucellosis or
phocine distemper virus, may spread to populations previously separated by the cold, or, in case of the
marine mammals, the sea ice.[95]
Marine ecosystems
The reduction of sea ice has brought more sunlight to the
phytoplankton and increased the annual
marine primary production in the Arctic by over 30% between 1998 and 2020.[1]: 2327 As the result, the Arctic Ocean became a stronger
carbon sink over this period;[96] yet, it still accounts for only 5% to 14% of the total ocean carbon sink, although it is expected to play a larger role in the future.[97] By 2100, phytoplankton
biomass in the Arctic Ocean is generally expected to increase by ~20% relative to 2000 under the low-emission scenario, and by 30-40% under the high-emission scenario.[1]: 2329
Atlantic cod have been able to move deeper into the Arctic due to the warming waters, while the
Polar cod and local
marine mammals have been losing habitat.[1]: 2327 Many
copepod species appear to be declining, which is also likely to reduce the numbers of fish which prey on them, such as
walleye pollock or the
arrowtooth flounder.[1]: 2327 This also affects Arctic
shorebirds. For instance, around 9000
puffins and other shorebirds in Alaska died of starvation in 2016, because too many fish have moved to the north.[98] While the shorebirds also appear to nest more successfully due to the observed warming,[99] this benefit may be more than offset by
phenological mismatch between shorebirds' and other species' life cycles.[100] Marine mammals such as
ringed seals and
walruses are also being negatively affected by the warming.[91][101]
Permafrost is an important component of hydrological systems and ecosystems within the Arctic landscape.[102] In the Northern Hemisphere the terrestrial permafrost domain comprises around 18 million km2.[103] Within this permafrost region, the total soil organic carbon (SOC) stock is estimated to be 1,460-1,600 Pg (where 1 Pg = 1 billion tons), which constitutes double the amount of carbon currently contained in the atmosphere.[104][105]
As recent warming deepens the active layer subject to permafrost thaw, this exposes formerly stored
carbon to biogenic processes which facilitate its entrance into the atmosphere as
carbon dioxide and
methane.[106] Because carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, it is a well-known example of a
positive climate change feedback,[107] and because widespread permafrost thaw is effectively irreversible, it is also considered one of
tipping points in the climate system.[108]
In the northern circumpolar region, permafrost contains organic matter equivalent to 1400–1650 billion tons of pure carbon, which was built up over thousands of years. This amount equals almost half of all organic material in all
soils,[109][106] and it is about twice the carbon content of the
atmosphere, or around four times larger than the human emissions of carbon between the start of the
Industrial Revolution and 2011.[110] Further, most of this carbon (~1,035 billion tons) is stored in what is defined as the near-surface permafrost, no deeper than 3 metres (9.8 ft) below the surface.[109][106] However, only a fraction of this stored carbon is expected to enter the atmosphere.[111] In general, the volume of permafrost in the upper 3 m of ground is expected to decrease by about 25% per 1 °C (1.8 °F) of global warming,[112]: 1283 yet even under the
RCP8.5 scenario associated with over 4 °C (7.2 °F) of global warming by the end of the 21st century,[113] about 5% to 15% of permafrost carbon is expected to be lost "over decades and centuries".[106]
Altogether, it is expected that cumulative greenhouse gas emissions from permafrost thaw will be smaller than the cumulative anthropogenic emissions, yet still substantial on a global scale, with some experts comparing them to emissions caused by
deforestation.[106] The
IPCC Sixth Assessment Report estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes of carbon dioxide per 1 °C (1.8 °F) of warming.[112]: 1237 For comparison, by 2019, annual anthropogenic emissions of carbon dioxide alone stood around 40 billion tonnes.[112]: 1237 A major review published in the year 2022 concluded that if the goal of preventing 2 °C (3.6 °F) of warming was realized, then the average annual permafrost emissions throughout the 21st century would be equivalent to the year 2019 annual emissions of Russia. Under RCP4.5, a scenario considered close to the current trajectory and where the warming stays slightly below 3 °C (5.4 °F), annual permafrost emissions would be comparable to year 2019 emissions of Western Europe or the United States, while under the scenario of high global warming and worst-case permafrost feedback response, they would approach year 2019 emissions of China.[106]
Fewer studies have attempted to describe the impact directly in terms of warming. A 2018 paper estimated that if global warming was limited to 2 °C (3.6 °F), gradual permafrost thaw would add around 0.09 °C (0.16 °F) to global temperatures by 2100,[114] while a 2022 review concluded that every 1 °C (1.8 °F) of global warming would cause 0.04 °C (0.072 °F) and 0.11 °C (0.20 °F) from abrupt thaw by the year 2100 and 2300. Around 4 °C (7.2 °F) of global warming, abrupt (around 50 years) and widespread collapse of permafrost areas could occur, resulting in an additional warming of 0.2–0.4 °C (0.36–0.72 °F).[108][115]
Black carbon deposits (from the combustion of heavy fuel oil (HFO) of Arctic shipping) absorb solar radiation in the atmosphere and strongly reduce the albedo when deposited on snow and ice, thus accelerating the effect of the melting of snow and sea ice.[117] A 2013 study quantified that
gas flaring at petroleum extraction sites contributed over 40% of the black carbon deposited in the Arctic.[118][119] 2019 research attributed the majority (56%) of Arctic surface black carbon to emissions from Russia, followed by European emissions, and Asia also being a large source.[120][117] In 2015, research suggested that reducing black carbon emissions and short-lived greenhouse gases by roughly 60 percent by 2050 could cool the Arctic up to 0.2 °C.[121] However, a 2019 study indicates that "Black carbon emissions will continuously rise due to increased shipping activities", specifically fishing vessels.[122]
The number of wildfires in the Arctic Circle has increased. In 2020, Arctic wildfire CO2 emissions broke a new record, peaking at 244 megatonnes of carbon dioxide emitted.[123] This is due to the burning of peatlands, carbon-rich soils that originate from the accumulation of waterlogged plants which are mostly found at Arctic latitudes.[123] These peatlands are becoming more likely to burn as temperatures increase, but their own burning and releasing of CO2 contributes to their own likelihood of burning in a positive feedback loop.[123]The smoke from wildfires defined as "
brown carbon" also increases arctic warming, with its warming effect is around 30% that of black carbon. As wildfires increases with warming this creates a
positive feedback loop.[124]
The
clathrate gun hypothesis is a proposed explanation for the periods of rapid warming during the
Quaternary. The hypothesis is that changes in fluxes in upper intermediate waters in the ocean caused temperature fluctuations that alternately accumulated and occasionally released
methane clathrate on upper continental slopes. This would have had an immediate impact on the global temperature, as
methane is a much more powerful
greenhouse gas than
carbon dioxide. Despite its atmospheric lifetime of around 12 years, methane's
global warming potential is 72 times greater than that of carbon dioxide over 20 years, and 25 times over 100 years (33 when accounting for
aerosol interactions).[125] It is further proposed that these warming events caused the
Bond Cycles and individual
interstadial events, such as the
Dansgaard–Oeschger interstadials.[126]
In 2018, a perspective piece devoted to
tipping points in the climate system suggested that the climate change contribution from methane hydrates would be "negligible" by the end of the century, but could amount to 0.4–0.5 °C (0.72–0.90 °F) on the millennial timescales.[127] In 2021, the
IPCC Sixth Assessment Report no longer included methane hydrates in the list of potential tipping points, and says that "it is very unlikely that CH4 emissions from clathrates will substantially warm the climate system over the next few centuries."[128] The report had also linked terrestrial hydrate deposites to
gas emission craters discovered in the
Yamal Peninsula in
Siberia, Russia beginning in July 2014,[129] but noted that since terrestrial gas hydrates predominantly form at a depth below 200 metres, a substantial response within the next few centuries can be ruled out.[128] Likewise, a 2022 assessment of tipping points described methane hydrates as a "threshold-free feedback" rather than a tipping point.[130][131]
AMOC has not always existed. For much of the Earth's history, overturning circulation in the Northern Hemisphere used to occur in the North Pacific. Paleoclimate evidence shows that the shift from the Pacific to Atlantic overturning circulation had occurred 34 million years ago, at the
Eocene-Oligocene transition, when the Arctic-Atlantic gateway had closed.[134] This closure fundamentally changed the thermohaline circulation structure - yet some researchers have suggested that
climate change may end up reversing this shift and re-establish the Pacific circulation after the AMOC shuts down.[135][136] This is because it affects the AMOC in two major ways - by making surface waters warmer as an inevitable consequence of
Earth's energy imbalance, and by making them less saline due to the addition of large quantities of fresh water from melting ice (mainly from
Greenland), and through increasing
precipitation over the North Atlantic. Both would increase the difference between the surface and lower layers, and thus make the upwelling and downwelling which drives the circulation more difficult.[137]
Severe weakening of the AMOC may lead to an outright collapse of the circulation, which would not be easily reversible and thus constitute one of the
tipping points in the climate system.[138] A collapse would substantially lower the average temperature and amount of
rain and snowfall in Europe.[139][140] It would also potentially raise the frequency of extreme weather events and have other severe effects.[141][142] Gold-standard
Earth system models indicate that a collapse is unlikely, and would only become plausible if high levels of warming (≥4 °C (7.2 °F))[139] are sustained well after the year 2100.[143][144][145] Some
paleoceanographic research seems to support this idea.[146][147] However, certain researchers fear that the complex models are too stable,[148] and lower-complexity projections pointing to an earlier collapse are more accurate.[149][150] One of those projections suggests that AMOC collapse could happen around 2057,[151] but many scientists are skeptical of the claim.[152] Some research also suggests that the Southern Ocean overturning circulation may be more prone to collapse than the AMOC.[153][141]
In 2021, the
IPCC Sixth Assessment Report again assessed that the AMOC is very likely to decline within the 21st century, and expressed high confidence that changes to it would be reversible within centuries if the warming was reversed.[154]: 19 Unlike the Fifth Assessment Report, it had only expressed medium confidence rather than high confidence in AMOC avoiding a collapse before the end of the century. This reduction in confidence was likely influenced by several review studies drawing attention to the circulation stability bias within
general circulation models,[155][156] as well as simplified ocean modelling studies suggesting that the AMOC may be more vulnerable to abrupt change than what the larger-scale models suggest.[149]
In 2022, an extensive assessment of all potential
climate tipping points identified 16 plausible climate tipping points, including a collapse of the AMOC. It suggested that a collapse would most likely be triggered by 4 °C (7.2 °F) of global warming, but that there's enough uncertainty to suggest it could be triggered at warming levels as low as 1.4 °C (2.5 °F), or as high as 8 °C (14 °F). Likewise, it estimates that once AMOC collapse is triggered, it would most likely take place over 50 years, but the entire range is between 15 and 300 years.[139][157] That assessment also treated the collapse of the
Northern Subpolar Gyre as a potential separate tipping point, which could occur at between 1.1 °C (2.0 °F) degrees and 3.8 °C (6.8 °F) (although this is only simulated by a fraction of climate models). The most likely figure is 1.8 °C (3.2 °F), and once triggered, the collapse of the gyre would most likely take 10 years from start to end, with a range between 5 and 50 years. The loss of this convection is estimated to lower the global temperature by 0.5 °C (0.90 °F), while the average temperature in Europe decreases by around 3 °C (5.4 °F). There are also substantial impacts on regional
precipitation.[139][157]
Since the early 2000s, climate models have consistently identified that global warming will gradually push jet streams poleward. In 2008, this was confirmed by observational evidence, which proved that from 1979 to 2001, the northern jet stream moved northward at an average rate of 2.01 kilometres (1.25 mi) per year, with a similar trend in the
Southern Hemisphere jet stream.[158][159] Climate scientists have hypothesized that the jet stream will also gradually weaken as a result of
global warming. Trends such as
Arctic sea ice decline, reduced snow cover,
evapotranspiration patterns, and other weather anomalies have caused the Arctic to heat up faster than other parts of the globe, in what is known as the
Arctic amplification. In 2021-2022, it was found that since 1979, the warming within the
Arctic Circle has been nearly four times faster than the global average,[160][161] and some hotspots in the
Barents Sea area warmed up to seven times faster than the global average.[162][163] While the Arctic remains one of the coldest places on Earth today, the temperature gradient between it and the warmer parts of the globe will continue to diminish with every decade of global warming as the result of this amplification. If this gradient has a strong influence on the jet stream, then it will eventually become weaker and more variable in its course, which would allow more cold air from the
polar vortex to leak
mid-latitudes and slow the progression of
Rossby waves, leading to more persistent and more
extreme weather.
The hypothesis above is closely associated with
Jennifer Francis, who had first proposed it in a 2012 paper co-authored by Stephen J. Vavrus.[164] While some paleoclimate reconstructions have suggested that the polar vortex becomes more variable and causes more unstable weather during periods of warming back in 1997,[165] this was contradicted by climate modelling, with PMIP2 simulations finding in 2010 that the
Arctic oscillation was much weaker and more negative during the
Last Glacial Maximum, and suggesting that warmer periods have stronger positive phase AO, and thus less frequent leaks of the polar vortex air.[166] However, a 2012 review in the Journal of the Atmospheric Sciences noted that "there [has been] a significant change in the vortex mean state over the twenty-first century, resulting in a weaker, more disturbed vortex.",[167] which contradicted the modelling results but fit the Francis-Vavrus hypothesis. Additionally, a 2013 study noted that the then-current
CMIP5 tended to strongly underestimate winter blocking trends,[168] and other 2012 research had suggested a connection between declining Arctic sea ice and heavy snowfall during midlatitude winters.[169]
However, because the specific observations are considered short-term observations, there is considerable uncertainty in the conclusions.
Climatology observations require several decades to definitively distinguish various forms of natural variability from climate trends.[170] This point was stressed by reviews in 2013[171] and in 2017.[172] A study in 2014 concluded that Arctic amplification significantly decreased cold-season temperature variability over the Northern Hemisphere in recent decades. Cold Arctic air intrudes into the warmer lower latitudes more rapidly today during autumn and winter, a trend projected to continue in the future except during summer, thus calling into question whether winters will bring more cold extremes.[173] A 2019 analysis of a data set collected from 35 182 weather stations worldwide, including 9116 whose records go beyond 50 years, found a sharp decrease in northern midlatitude cold waves since the 1980s.[174]
Moreover, a range of long-term observational data collected during 2010s and published in 2020s now suggests that the intensification of Arctic amplification since the early 2010s was not linked to significant changes on midlatitude atmospheric patterns.[175][176] State-of-the-art modelling research of PAMIP (Polar Amplification Model Intercomparison Project) improved upon the 2010 findings of PMIP2 - it did find that sea ice decline would weaken the jet stream and increase the probability of atmospheric blocking, but the connection was very minor, and typically insignificant next to interannual variability.[177][178] In 2022, a follow-up study found that while the PAMIP average had likely underestimated the weakening caused by sea ice decline by 1.2 to 3 times, even the corrected connection still amounts to only 10% of the jet stream's natural variability.[179]
Growing evidence that global warming is shrinking polar ice has added to the urgency of several nations'
Arctic territorial claims in hopes of establishing resource development and
new shipping lanes, in addition to protecting sovereign rights.[180]
As ice sea coverage decreases more and more, year on year, Arctic countries (Russia, Canada, Finland, Iceland, Norway, Sweden, the United States and Denmark representing Greenland) are making moves on the geopolitical stage to ensure access to potential
new shipping lanes, oil and gas reserves, leading to overlapping claims across the region.[181] However, there is only one single land border dispute in the Arctic, with all others relating to the sea, that is
Hans Island.[182] This small uninhabited island lies in the
Nares strait, between Canada's
Ellesmere Island and the northern coast of Greenland. Its status comes from its geographical position, right between the equidistant boundaries determined in a 1973 treaty between Canada and Denmark.[182] Even though both countries have acknowledged the possibility of splitting the island, no agreement on the island has been reached, with both nations still claiming it for themselves.[182]
There is more activity in terms of maritime boundaries between countries, where overlapping claims for
internal waters,
territorial seas and particularly
Exclusive Economic Zones (EEZs) can cause frictions between nations. Currently, official maritime borders have an unclaimed triangle of international waters lying between them, that is at the centerpoint of international disputes.[181]
This unclaimed land can be obtainable by submitting a claim to the
United Nations Convention on the Law of the Sea, these claims can be based on geological evidence that continental shelves extend beyond their current maritime borders and into international waters.[181]
Some overlapping claims are still pending resolution by international bodies, such as a large portion containing the
north pole that is both claimed by Denmark and Russia, with some parts of it also contested by Canada.[181] Another example is that of the
Northwest Passage, globally recognized as international waters, but technically in Canadian waters.[181] This has led to Canada wanting to limit the number of ships that can go through for environmental reasons but the United States disputes that they have the authority to do so, favouring unlimited passage of vessels.[181]
Navigation
The
Transpolar Sea Route is a future Arctic shipping lane running from the Atlantic Ocean to the Pacific Ocean across the center of the Arctic Ocean. The route is also sometimes called Trans-Arctic Route. In contrast to the
Northeast Passage (including the
Northern Sea Route) and the
North-West Passage it largely avoids the territorial waters of Arctic states and lies in international high seas.[183]
Governments and private industry have shown a growing interest in the Arctic.[184] Major new shipping lanes are opening up:
the northern sea route had 34 passages in 2011 while the
Northwest Passage had 22 traverses, more than any time in history.[185] Shipping companies may benefit from the shortened distance of these northern routes. Access to natural resources will increase, including valuable minerals and offshore oil and gas.[186] Finding and controlling these resources will be difficult with the continually moving ice.[186] Tourism may also increase as less sea ice will improve safety and accessibility to the Arctic.[186]
The melting of Arctic ice caps is likely to increase traffic in and the commercial viability of the Northern Sea Route. One study, for instance, projects, "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."[187]
As of 2021, there are 1162 settlements located directly atop the Arctic permafrost, which host an estimated 5 million people. By 2050, permafrost layer below 42% of these settlements is expected to thaw, affecting all their inhabitants (currently 3.3 million people).[188] Consequently, a wide range of infrastructure in permafrost areas is threatened by the thaw.[189][190]: 236 By 2050, it's estimated that nearly 70% of global infrastructure located in the permafrost areas would be at high risk of permafrost thaw, including 30–50% of "critical" infrastructure. The associated costs could reach tens of billions of dollars by the second half of the century.[191] Reducing
greenhouse gas emissions in line with the
Paris Agreement is projected to stabilize the risk after mid-century; otherwise, it'll continue to worsen.[192]
In
Alaska alone, damages to infrastructure by the end of the century would amount to $4.6 billion (at 2015 dollar value) if
RCP8.5, the high-emission
climate change scenario, were realized. Over half stems from the damage to buildings ($2.8 billion), but there's also damage to roads ($700 million), railroads ($620 million), airports ($360 million) and
pipelines ($170 million).[193] Similar estimates were done for RCP4.5, a less intense scenario which leads to around 2.5 °C (4.5 °F) by 2100, a level of warming similar to the current projections.[194] In that case, total damages from permafrost thaw are reduced to $3 billion, while damages to roads and railroads are lessened by approximately two-thirds (from $700 and $620 million to $190 and $220 million) and damages to pipelines are reduced more than ten-fold, from $170 million to $16 million. Unlike the other costs stemming from climate change in Alaska, such as damages from increased
precipitation and flooding,
climate change adaptation is not a viable way to reduce damages from permafrost thaw, as it would cost more than the damage incurred under either scenario.[193]
In Canada,
Northwest Territories have a population of only 45,000 people in 33 communities, yet permafrost thaw is expected to cost them $1.3 billion over 75 years, or around $51 million a year. In 2006, the cost of adapting
Inuvialuit homes to permafrost thaw was estimated at $208/m2 if they were built at pile foundations, and $1,000/m2 if they didn't. At the time, the average area of a residential building in the territory was around 100 m2. Thaw-induced damage is also unlikely to be covered by
home insurance, and to address this reality, territorial government currently funds Contributing Assistance for Repairs and Enhancements (CARE) and Securing Assistance for Emergencies (SAFE) programs, which provide long- and short-term forgivable loans to help homeowners adapt. It is possible that in the future, mandatory relocation would instead take place as the cheaper option. However, it would effectively tear the local
Inuit away from their ancestral homelands. Right now, their average personal income is only half that of the median NWT resident, meaning that adaptation costs are already disproportionate for them.[195]
By 2022, up to 80% of buildings in some Northern Russia cities had already experienced damage.[191] By 2050, the damage to residential infrastructure may reach $15 billion, while total public infrastructure damages could amount to 132 billion.[196] This includes
oil and gas extraction facilities, of which 45% are believed to be at risk.[192]
For much of the 20th century, it was believed that permafrost would "indefinitely" preserve anything buried there, and this made deep permafrost areas popular locations for hazardous waste disposal. In places like Canada's
Prudhoe Bay oil field, procedures were developed documenting the "appropriate" way to inject waste beneath the permafrost. This means that as of 2023, there are ~4500 industrial facilities in the Arctic permafrost areas which either actively process or store hazardous chemicals. Additionally, there are between 13,000 and 20,000 sites which have been heavily contaminated, 70% of them in Russia, and their pollution is currently trapped in the permafrost. About a fifth of both the industrial and the polluted sites (1000 and 2200–4800) are expected to start thawing in the future even if the warming does not increase from its 2020 levels. Only about 3% more sites would start thawing between now and 2050 under the climate change scenario consistent with the
Paris Agreement goals,
RCP2.6, but by 2100, about 1100 more industrial facilities and 3500 to 5200 contaminated sites are expected to start thawing even then. Under the very high emission scenario RCP8.5, 46% of industrial and contaminated sites would start thawing by 2050, and virtually all of them would be affected by the thaw by 2100.[197]Organochlorines and other
persistent organic pollutants are of a particular concern, due to their potential to repeatedly reach local communities after their re-release through
biomagnification in fish. At worst, future generations born in the Arctic would enter life with weakened
immune systems due to pollutants accumulating across generations.[198]
A notable example of pollution risks associated with permafrost was the
2020 Norilsk oil spill, caused by the collapse of
diesel fuel storage tank at Norilsk-Taimyr Energy's
thermal power plant No. 3. It spilled 6,000 tonnes of fuel into the land and 15,000 into the water, polluting
Ambarnaya,
Daldykan and many smaller rivers on
Taimyr Peninsula, even reaching lake
Pyasino, which is a crucial water source in the area.
State of emergency at the federal level was declared.[199][200] The event has been described as the second-largest oil spill in modern Russian history.[201][202]
Another issue associated with permafrost thaw is the release of natural
mercury deposits. An estimated 800,000 tons of mercury are frozen in the permafrost soil. According to observations, around 70% of it is simply taken up by vegetation after the thaw.[198] However, if the warming continues under RCP8.5, then permafrost emissions of mercury into the
atmosphere would match the current global emissions from all human activities by 2200. Mercury-rich soils also pose a much greater threat to humans and the environment if they thaw near rivers. Under RCP8.5, enough mercury will enter the
Yukon River basin by 2050 to make its fish unsafe to eat under the
EPA guidelines. By 2100, mercury concentrations in the river will double. Contrastingly, even if mitigation is limited to RCP4.5 scenario, mercury levels will increase by about 14% by 2100, and will not breach the EPA guidelines even by 2300.[203]
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.[204][205] 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.[206] 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.[207][208]
Impacts on indigenous peoples
As climate change speeds up, it is having more and more of a direct impact on societies around the world. This is particularly true of people that live in the Arctic, where increases in temperature are occurring at faster rates than at other latitudes in the world, and where traditional ways of living, deeply connected with the natural arctic environment are at particular risk of environmental disruption caused by these changes.[186]
The warming of the atmosphere and ecological changes that come alongside it presents challenges to local communities such as the
Inuit. Hunting, which is a major way of survival for some small communities, will be changed with increasing temperatures.[209] The reduction of sea ice will cause certain species populations to decline or even become extinct.[186] Inuit communities are deeply reliant on seal hunting, which is dependent on sea ice flats, where seals are hunted.[210]
Unsuspected changes in river and snow conditions will cause herds of animals, including reindeer, to change migration patterns,
calving grounds, and
forage availability.[186] In good years, some communities are fully employed by the commercial harvest of certain animals.[209] The harvest of different animals fluctuates each year and with the rise of temperatures it is likely to continue changing and creating issues for Inuit hunters, as unpredictability and disruption of ecological cycles further complicate life in these communities, which already face significant problems, such as Inuit communities being the poorest and most unemployed of North America.[210]
Other forms of transportation in the Arctic have seen negative impacts from the current warming, with some transportation routes and pipelines on land being disrupted by the melting of ice.[186] Many Arctic communities rely on frozen roadways to transport supplies and travel from area to area.[186] The changing landscape and unpredictability of weather is creating new challenges in the Arctic.[211] Researchers have documented historical and current trails created by the Inuit in the
Pan Inuit Trails Atlas, finding that the change in sea ice formation and breakup has resulted in changes to the routes of trails created by the Inuit.[212]
International Arctic Buoy Program: deploys and maintains buoys that provide real-time position, pressure, temperature, and interpolated ice velocity data
'Role of the Arctic Region', in conjunction with the
International Polar Year, was the focus of the second international conference on Global Change Research, held in
Nynäshamn,
Sweden, October 2007.[216]
SEARCH (
Study of Environmental Arctic Change): A research framework originally promoted by several US agencies; an international extension is ISAC (the International Study of Arctic Change[217]).
The 2021
Arctic Monitoring and Assessment Programme (AMAP) report by an international team of more than 60 experts, scientists, and indigenous knowledge keepers from Arctic communities, was prepared from 2019 to 2021.[218]: vii It is a follow-up report of the 2017 assessment, "Snow, Water, Ice and Permafrost in the Arctic" (SWIPA).[218]: vii The 2021 IPCC AR6 WG1 Technical Report confirmed that "[o]bserved and projected warming" were ""strongest in the Arctic".[219]: 29 According to an 11 August 2022 article published in Nature, there have been numerous reports that the Arctic is warming from twice to three times as fast as the global average since 1979, but the co-authors cautioned that the recent report of the "four-fold Arctic warming ratio" was potentially an "extremely unlikely event".[220] The annual mean Arctic Amplification (AA) index had "reached values exceeding four" from c. 2002 through 2022, according to a July 2022 article in Geophysical Research Letters.[221]: 1 [222]
The 14 December 2021 16th Arctic Report Card produced by the United States's
National Oceanic and Atmospheric Administration (NOAA) and released annually, examined the "interconnected physical, ecological and human components" of the circumpolar Arctic.[223][46] The report said that the 12 months between October 2020 and September 2021 were the "seventh warmest over Arctic land since the record began in 1900".[223] The 2017 report said that the melting ice in the warming Arctic was unprecedented in the past 1500 years.[213][214] NOAA's State of the Arctic Reports, starting in 2006, updates some of the records of the original 2004 and 2005
Arctic Climate Impact Assessment (ACIA) reports by the intergovernmental
Arctic Council and the non-governmental
International Arctic Science Committee.[224]
A 2022
United Nations Environment Programme (UNEP) report "Spreading Like Wildfire: The Rising Threat Of Extraordinary Landscape Fires" said that smoke from wildfires around the world created a
positive feedback loop that is a contributing factor to Arctic melting.[225][124] The
2020 Siberian heatwave was "associated with extensive burning in the Arctic Circle".[225]: 36 Report authors said that this extreme heat event was the first to demonstrate that it would have been "almost impossible" without anthropogenic emissions and climate change.[226][225]: 36
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