Climate change in Antarctica

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infrared observations made by a series of NOAA satellite sensors.

Climate change caused by greenhouse gas emissions from human activities occurs everywhere on Earth, and while Antarctica is less vulnerable to it than any other continent,[1] climate change in Antarctica has already been observed. There has been an average temperature increase of >0.05 °C/decade since 1957 across the continent, although it had been uneven.[2] While West Antarctica warmed by over 0.1 °C/decade from the 1950s to the 2000s and the exposed Antarctic Peninsula has warmed by 3 °C (5.4 °F) since the mid-20th century,[3] the colder and more stable East Antarctica had been experiencing cooling until the 2000s.[4][5] Around Antarctica, the Southern Ocean has absorbed more heat than any other ocean,[6] with particularly strong warming at depths below 2,000 m (6,600 ft)[7]: 1230  and around the West Antarctic, which has warmed by 1 °C (1.8 °F) since 1955.[3]

The warming of Antarctica's territorial waters has caused the weakening or outright collapse of ice shelves, which float just offshore of glaciers and stabilize them. Many coastal glaciers have been losing mass and retreating, which causes net annual ice loss across Antarctica,[7]: 1264  even as the East Antarctic ice sheet continues to gain ice inland. By 2100, net ice loss from Antarctica alone is expected to add about 11 cm (5 in) to global sea level rise. However, marine ice sheet instability may cause West Antarctica to contribute tens of centimeters more if it is triggered before 2100.[7]: 1270  With higher warming instability would be much more likely, and could double overall 21st century sea level rise.[8][9][10]

The fresh meltwater from the ice, 1100-1500 billion tons (GT) per year, dilutes the saline Antarctic bottom water,[11][12] thus weakening the lower cell of the Southern Ocean overturning circulation.[7]: 1240  Some research tentatively suggests a full collapse of the circulation may occur between 1.7 °C (3.1 °F) and 3 °C (5.4 °F) of global warming,[13] although the full effects are expected to unfold over multiple centuries. They include less precipitation in the Southern Hemisphere but more in the Northern Hemisphere, and an eventual decline of fisheries in the Southern Ocean with a potential collapse of certain marine ecosystems.[14] Furthermore, while many Antarctic species remain undiscovered, there are already documented increases in flora and large fauna such as penguins are already seen struggling to retain suitable habitat. On ice-free land, permafrost thaws, releasing not only greenhouse gases, but also formerly frozen pollution.[15]

The West Antarctic ice sheet is likely to melt completely,[16][17][18]unless temperatures are reduced by 2 °C (3.6 °F) below the levels of the year 2020.[19] The loss of this ice sheet would take between 2,000 and 13,000 years,[20][21] although several centuries of high emissions could shorten this timeframe to 500 years.[22] A sea-level rise of 3.3 m (10 ft 10 in) would occur if the ice sheet collapses leaving ice caps on the mountains and 4.3 m (14 ft 1 in) if those ice caps also melt.[23] Isostatic rebound may contribute an additional 1 m (3 ft 3 in) to global sea levels over another 1,000 years.[22] In contrast, the East Antarctic ice sheet is far more stable and may only cause a sea-level rise of 0.5 m (1 ft 8 in) - 0.9 m (2 ft 11 in) from the current level of warming, a small fraction of the 53.3 m (175 ft) contained in the full ice sheet.[24] With a global warming of around 3 °C (5.4 °F), vulnerable areas like the Wilkes Basin and Aurora Basin may collapse over a period of around 2,000 years,[20][21] potentially adding up to 6.4 m (21 ft 0 in) to sea levels.[22] The complete melting and disappearance of the East Antarctic ice sheet would require at least 10,000 years, and it would only occur if global warming reaches 5 °C (9.0 °F) to 10 °C (18 °F).[20][21]

Temperature and weather changes[edit]

greenhouse effect during certain months of the year. At greater warming levels, this effect is likely to disappear due to increasing concentrations of water vapor over Antarctica[25]

Antarctica is the coldest and driest continent on Earth, as well as the one with the highest average elevation.[1] Because Antarctica is so dry, there is little water vapor, so its air doesn't conduct heat well.[25] Further, it is surrounded by the Southern Ocean, which is far more effective at absorbing heat than any other ocean.[26] It also has extensive year-around sea ice, which has a high albedo (reflectivity) and adds to the albedo of the ice's sheet own bright, white surface.[1] Antarctica is so cold that it is the only place on Earth where atmospheric temperature inversion occurs every winter.[1] Elsewhere, the atmosphere on Earth is at its warmest near the surface and it becomes cooler as elevation increases. During the Antarctic winter, the surface of central Antarctica instead becomes cooler than middle layers of the atmosphere.[25] This means that greenhouse gases trap heat in the middle atmosphere and reduce its flow towards the surface and towards space, instead of simply preventing the flow of heat from the lower atmosphere to the upper layers. This effect lasts until the end of the Antarctic winter.[25][1] Thus, even the early climate models predicted that temperature trends over Antarctica would emerge slower and be more subtle than they are elsewhere.[27]

Moreover, there were fewer than twenty permanent weather stations across the continent, with only two in the continent's interior, while automatic weather stations were deployed relatively late, and their observational record was brief for much of the 20th century. Likewise, satellite temperature measurements did not begin until 1981 and are typically limited to cloud-free conditions. Thus datasets representing the entire continent only began to appear by the very end of the 20th century.[28] The only exception was the Antarctic Peninsula, where warming was both well-documented and strongly pronounced:[29] It was eventually found to have warmed by 3 °C (5.4 °F) since the mid-20th century.[3] Based on this limited data, several papers published in the early 2000s suggested that there had been an overall cooling over continental Antarctica (that is outside of the Peninsula).[30][31]

[2]

A 2002 analysis led by Peter Doran received widespread media coverage after it also indicated stronger cooling than warming between 1966 and 2000, and found that McMurdo Dry Valleys in East Antarctica had experienced cooling of 0.7 °C per decade[32] - a local trend confirmed by subsequent research at McMurdo.[33] Multiple journalists suggested that these findings were "contradictory" to global warming,[34][35][36][37][38][39] even though the paper itself noted the limited data, and still found warming over 42% of the continent.[32][40][41] What became known as the "Antarctic Cooling Controversy" received further attention in 2004, when Michael Crichton wrote a novel State of Fear which alleged a conspiracy amongst climate scientists to make up global warming, and claimed that Doran's study definitively proved there was no warming in Antarctica outside of the Peninsula.[42] Relatively few scientists responded to the book at the time,[43] but it was subsequently brought up in a 2006 US Senate hearing in support of climate change denial,[44] and Peter Doran felt compelled to publish a statement in The New York Times decrying the misinterpretation of his work.[40] The British Antarctic Survey and NASA also issued statements affirming the strength of climate science after the hearing.[45][46]

By 2009, research was finally able to combine historical weather station data with satellite measurements to create consistent temperature records going back to 1957, which demonstrated warming of >0.05 °C/decade since 1957 across the continent, with cooling in East Antractica offset by the average temperature increase of at least 0.176 ± 0.06 °C per decade in West Antarctica.[2][47] Subsequent research confirmed clear warming over West Antarctica in the 20th century with the only uncertainty being the magnitude.[48] Over 2012-2013, estimates based on WAIS Divide ice cores and the revised Byrd Station temperature record even suggested a much larger West Antarctica warming of 2.4 °C (4.3 °F) since 1958, or around 0.46 °C (0.83 °F) per decade,[49][50][51][52] although there has been some uncertainty about it.[53] In 2022, a study narrowed the warming of the Central area of the West Antarctic Ice Sheet between 1959 and 2000 to 0.31 °C (0.56 °F) per decade, and conclusively attributed it to increases in greenhouse gas concentrations caused by human activity.[54]

[5]

Local changes in atmospheric circulation patterns like the Interdecadal Pacific Oscillation or the Southern Annular Mode, slowed or even partially reversed the warming of West Antarctica between 2000 and 2020, with the Antarctic Peninsula experiencing cooling from 2002.[55][56][57] While a variability in those patterns is natural, ozone depletion had also led the Southern Annular Mode (SAM) to be stronger than it had been in the past 600 years of observations. Studies predicted a reversal in the SAM once the ozone layer began to recover following the Montreal Protocol starting from 2002,[58][59][60] and these changes were consistent with their predictions.[61] As these patterns reversed, the East Antarctica interior demonstrated clear warming over those two decades.[5][62] In particular, the South Pole warmed by 0.61 ± 0.34 °C per decade between 1990 and 2020, which is three times the global average.[4][63] The Antarctica-wide warming trend also continued after 2000, and in February 2020, the continent recorded its highest temperature of 18.3 °C, which was a degree higher than the previous record of 17.5 °C in March 2015.[64]

Models predict that under the most intense climate change scenario, known as RCP8.5, Antarctic temperatures will be up 4 °C (7.2 °F), on average, by 2100 and this will be accompanied by a 30% increase in precipitation and a 30% decrease in total sea ice.[65] RCPs were developed in the late 2000s, and early 2020s research considers RCP8.5 much less likely[66] than the more "moderate" scenarios like RCP 4.5, which lies in between the worst-case and the Paris Agreement goals.[67][68]

Black carbon and effects on albedo[edit]

Black carbon accumulated on snow and ice reduces the reflection of ice causing it to absorb more energy and accelerate melting. This can create an ice-albedo feedback loop where meltwater itself absorbs more sunlight.[69] Black carbon is an impurity which darkens snow and other icy surfaces. This causes more solar energy to be absorbed, which melts more snow.[70] In Antarctica black carbon has been found on the Antarctic Peninsula and around Union Glacier, with the highest concentrations near human activities.[71][72] The result of human activities in Antarctica will accelerate snowmelt on the continent,[clarification needed] but the speed of melting will differ depending on how far black carbon and other emissions will spread, along with the size of the area that they will cover. A study from 2022 estimate that the seasonal melt during the summer period will start sooner on sites with black carbon because of the reduction in albedo reflection that ranges from 5 to 23 kg/m2.[72][clarification needed]

Effects on ocean currents[edit]

[66][68] the Southern Ocean would continue to take up an increasing amount of carbon dioxide (left) and heat (middle) during the 21st century.[6] However, it would take up a smaller fraction of heat (right) and emissions per every additional degree of warming when compared to now.[6][73]

Main article: Southern Ocean overturning circulation

See also: Effects of climate change on oceans

Between 1971 and 2018, over 90% of thermal energy from global heating entered the oceans.[74] Southern Ocean absorbs the most heat by far - after 2005, it accounted for between 67% and 98% of all heat entering the oceans.[26] The temperature in the upper layer of the ocean in West Antarctica has warmed 1 °C (1.8 °F) since 1955, and the Antarctic Circumpolar Current (ACC) is also warming faster than the average.[3] It is also a highly important carbon sink.[75][76] These properties are connected to Southern Ocean overturning circulation, one half of the global thermohaline circulation. It is so important that estimates on when global warming will reach 2 °C (3.6 °F) (inevitable in all scenarios where greenhouse gas emissions have not been strongly lowered) depend on the strength of the circulation more than any factor other than the overall emissions.[13]

[77]

The overturning circulation itself consists of two parts - the smaller upper cell, which is most strongly affected by winds and precipitation, and the larger lower cell, which is defined by the temperature and salinity of Antarctic bottom water.[78] Since the 1970s, the upper cell has strengthened by 50-60%, while the lower cell has weakened by 10-20%.[79][77] Some of this was due to the natural cycle of Interdecadal Pacific Oscillation, but there is also a clear impact of climate change,[80][81] as it alters winds and precipitation through shifts in the Southern Annular Mode pattern,[26] while the salty Antarctic bottom water is diluted by fresh meltwater from the erosion of the West Antarctic ice sheet,[11][12] which flows at a rate of 1100-1500 billion tons (GT) per year.[7]: 1240  During the 2010s, a temporary reduction in ice shelf melting in West Antarctica had allowed for the partial recovery of Antarctic bottom water and the lower cell of the circulation.[82] Yet, greater melting and more decline of the circulation is expected in the future.[83]

As bottom water weakens while the flow of warmer, fresher waters strengthens near the surface, the surface waters become more buoyant and less likely to sink and mix with the lower layers. Consequently, ocean stratification increases.[84][79][77] One study suggests that the circulation would lose half its strength by 2050 under the worst climate change scenario,[83] with greater losses occurring afterwards.[14] Paleoclimate evidence shows that the entire circulation has weakened a lot or completely collapsed in the past: some preliminary research suggests that such a collapse may become likely once global warming reaches levels between 1.7 °C (3.1 °F) and 3 °C (5.4 °F), but this estimate is much less certain than for the majority of tipping points in the climate system.[13] Such a collapse would also be prolonged: one estimate indicates it would occur some time before 2300.[85] As with the better-studied AMOC, a major slowdown or collapse of the Southern ocean circulation would have substantial regional and global impacts.[13] Some likely impacts include a decline in precipitation in the Southern Hemisphere countries like Australia (with a corresponding increase in the Northern Hemisphere), and an eventual decline of fisheries in the Southern Ocean, which could lead to a potential collapse of certain marine ecosystems.[14] These impacts are expected to unfold over multiple centuries,[14] but there has been limited research to date and few specifics are currently known.[13]

Impacts on the cryosphere[edit]

Observed changes in ice mass[edit]

Duration: 37 seconds.

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Contrasting temperature trends across parts of Antarctica, as well as its remoteness, mean that some locations lose mass, particularly at the coasts, while others that are more inland continue to gain it, and estimating an average trend can be difficult.[86] In 2018, a systematic review of all previous studies and data by the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) estimated an increase in West Antarctic ice sheet annual mass loss from 53 ± 29 Gt (gigatonnes) in 1992 to 159 ± 26 Gt in the final five years of the study. On the Antarctic Peninsula, the study estimated −20 ± 15 Gt per year with an increase in loss of roughly 15 Gt per year after year 2000, with a significant role played by the loss of ice shelves.[87] The review's overall estimate was that Antarctica lost 2720 ± 1390 gigatons of ice from 1992 to 2017, averaging 109 ± 56 Gt per year. This would amount to 7.6 millimeters of sea level rise.[87] Then, though, a 2021 analysis of data from four different research satellite systems (Envisat, European Remote-Sensing Satellite, GRACE and GRACE-FO and ICESat) indicated annual mass loss of only about 12 Gt from 2012-2016, due to much greater ice gain in East Antarctica than estimated earlier, which had offset most of the losses from West Antarctica.[88] The East Antarctic ice sheet can still gain mass in spite of warming because effects of climate change on the water cycle increase precipitation over its surface, which then freezes and helps to build up more ice.[7]: 1262

21st century ice loss and sea level rise[edit]

[89]

By 2100, net ice loss from Antarctica alone is expected to add about 11 cm (5 in) to global sea level rise.[7]: 1270  However, processes such as marine ice sheet instability, which describes the potential for warm water currents to enter between the seafloor and the base of the ice sheet once it is no longer heavy enough to displace such flows,[90] and marine ice cliff instability, when ice cliffs with heights greater than 100 m (330 ft) may collapse under their own weight once they are no longer buttressed by ice shelves (which has never been observed, and only occurs in some of the modelling)[91] may cause West Antarctica have a much larger contribution. Such processes may increase sea level rise caused by Antarctica to 41 cm (16 in) by 2100 under the low-emission scenario and 57 cm (22 in) under the high-emission scenario.[7]: 1270  Some scientists have even larger estimates, but all agree it would have a greater impact and become much more likely to occur under higher warming scenarios, where it may double the overall 21st century sea level rise to 2 meters or more.[8][9][10] One study suggested that if the Paris Agreement is followed and global warming is limited to 2 °C (3.6 °F), the loss of ice in Antarctica will continue at the 2020 rate for the rest of the century, but if a trajectory leading to 3 °C (5.4 °F) is followed, Antarctica ice loss will accelerate after 2060 and start adding 0.5 cm to global sea levels per year by 2100.[92]

Long-term sea level rise[edit]

greenhouse gas emissions significantly (lowest trace), then sea level rise by 2100 can be limited to 0.3–0.6 m (1–2 ft).[93] If the emissions instead accelerate rapidly (top trace), sea levels could rise 5 m (16

+

1⁄2 ft) by the year 2300. Higher levels of sea level rise would involve substantial ice loss from Antarctica, including East Antarctica.[93]

Sea level rise will continue well after 2100, but potentially at very different rates. According to the most recent reports of the Intergovernmental Panel on Climate Change (SROCC and the IPCC Sixth Assessment Report), there will be a median rise of 16 cm (6.3 in) and maximum rise of 37 cm (15 in) under the low-emission scenario. On the other hand, the highest emission scenario results in a median rise of 1.46 m (5 ft) metres, with a minimum of 60 cm (2 ft) and a maximum of 2.89 m (9

+

1⁄2 ft)).[7]

Over even longer timescales, West Antarctic ice sheet, which is much smaller than the East Antarctic ice sheet is and grounded deep below the sea level, is considered highly vulnerable. The melting of all the ice in West Antarctica would increase the total sea level rise to 4.3 m (14 ft 1 in).[23] However, mountain ice caps not in contact with water are less vulnerable than the majority of the ice sheet, which is located below the sea level. Its collapse would cause ~3.3 m (10 ft 10 in) of sea level rise.[94] This kind of collapse is now considered practically inevitable, because it appears to have already occurred during the Eemian period 125,000 years ago, when temperatures were similar to the early 21st century.[95][96][16][17][97] The Amundsen Sea also appears to be warming at rates which would make the ice sheet's collapse effectively inevitable.[18][98]

The only way to reverse ice loss from West Antarctica once triggered is by lowering the global temperature to 1 °C (1.8 °F) below the preindustrial level. This would be 2 °C (3.6 °F) below the temperature of 2020.[19] Other researchers suggested that a climate engineering intervention to stabilize the ice sheet's glaciers may delay its loss by centuries and give more time to adapt. However this is an uncertain proposal, and would end up as one of the most expensive projects ever attempted.[99][100] Otherwise, the disappearance of the West Antarctic ice sheet would take an estimated 2000 years. The absolute minimum for the loss of West Antarctica ice is 500 years, and the potential maximum is 13,000 years.[20][21] Once the ice sheet is lost, there would also be an additional 1 m (3 ft 3 in) of sea level rise over the next 1000 years, caused by isostatic rebound of land beneath the ice sheet.[22]

Cook Glacier - a key part of the Wilkes Basin - during the Eemian ~120,000 years ago and an earlier Pleistocene interglacial ~330,000 years ago. These retreats would have added about 0.5 m (1 ft 8 in) and 0.9 m (2 ft 11 in) to sea level rise.[24]

On the other hand, the East Antarctic Ice Sheet as a whole is far more stable. It would take global warming in a range between 5 °C (9.0 °F) and 10 °C (18 °F), and a minimum of 10,000 years for the entire ice sheet to be lost.[20][21] Yet, some of its parts, such as Totten Glacier and Wilkes Basin, are located in vulnerable locations below the sea level, known as subglacial basins. Estimates suggest that they would be committed to disappearance once the global warming reaches 3 °C (5.4 °F), although the plausible temperature range is between 2 °C (3.6 °F) and 6 °C (11 °F). Once it becomes too warm for these subglacial basins, their collapse would unfold over a period of around 2,000 years, although it may be as fast as 500 years or as slow as 10,000 years.[20][21]

The loss of all this ice would ultimately add between 1.4 m (4 ft 7 in) and 6.4 m (21 ft 0 in) to sea levels, depending on the ice sheet model used. Isostatic rebound of the newly ice-free land would also add 8 cm (3.1 in) and 57 cm (1 ft 10 in), respectively.[22] Evidence from the Pleistocene shows that partial loss can also occur at lower warming levels: Wilkes Basin is estimated to have lost enough ice to add 0.5 m (1 ft 8 in) to sea levels between 115,000 and 129,000 years ago, during the Eemian, and about 0.9 m (2 ft 11 in) between 318,000 and 339,000 years ago, during the Marine Isotope Stage 9.[24]

Permafrost thaw[edit]

Antarctica has much less permafrost than the Arctic,[67] but what is there is also subject to thaw. Similar to how soils have a variety of chemical contaminants and nutrients in them, the permafrost in Antarctica traps various compounds. These include persistent organic pollutants (POPs) like polycyclic aromatic hydrocarbons, many of which are known carcinogens or can cause liver damage,[101] and polychlorinated biphenyls such as HCB or DDT, which are associated with decreased reproductive success and immunohematological disorders,.[102] There are also heavy metals like mercury, lead and cadmium, which can cause endocrine disruption, DNA damage, immunotoxicity and reproductive toxicity.[103] If or when contaminated permafrost thaws, these compounds are released again. This can change the chemistry of surface waters, and bioaccumulate and biomagnify these compounds throughout the food chain.[15] Permafrost thaw also results in greenhouse gas emissions, but the limited volume of Antarctic permafrost means that it is not considered important for climate change relative to the Arctic permafrost.[67]

Impacts on ecology[edit]

See also: Wildlife of Antarctica

Biodiversity loss[edit]

See also: Biodiversity loss

According to the Register of Antarctic Marine Species, 8,806 species had been discovered in Antarctica by 2010, yet estimates of undiscovered species suggest that there could be as many as 17,000 species in total.[104] Modern research techniques have found some species including bivalves, isopods, and pycnogonida in the Antarctic ecosystem. For instance, cruises such as ANDEEP (Antarctic, benthic deep-sea biodiversity project) sampled around 11% of the deep sea, where they found 585 species of isopod crustaceans that were previously undescribed.[105] Further research of the deep sea Antarctic is likely to yield new discoveries about its biodiversity, as while 90% of the Antarctic region is greater than 1,000 m (3,281 ft) deep, only 30% of the benthic sample locations were taken at that depth.[105]

Earlier research assumed that Antarctic biodiversity might be unaffected by climate change.[106] This is no longer held to be the case,[107] yet all but a few Antarctic species still lack detailed assessments of their vulnerability.[108] Some research suggests that at 3 °C (5.4 °F) of warming, Antarctic species richness would decline by nearly 17% and the suitable climate area by 50%.[109]

Plants[edit]

The continental flora in Antarctica is dominated by lichens, followed by mosses and ice algae. The plants are mainly found in coastal areas in Antarctica. The only vascular plants on continental Antarctica, Deschampsia antarctica and Colobanthus quitensis, are found on the Antarctic Peninsula. Because of changing climatic conditions, adaptation to the new conditions is necessary for the survival of the plants.[110] One way to deal with the problem is to grow fast when conditions are favourable. High concentrations of carbon dioxide and other greenhouse gases in the atmosphere cause climate change with increase in temperature, which leads to (I) increase in water availability, which in turn leads to (II) increase in plant colonization and (III) local-scale population expansion, which leads to (IV) increase in biomass, trophic complexity, and increased terrestrial diversity, and (V) more complex ecosystem structure, and (VI) dominance of biotic factors that drive processes in the ecosystem.

Deschampsia antarctica and Colobanthus quitensis.

Increased photosynthesis because of elevated temperatures has been shown in two maritime vascular species (Deschampsia antarctica and Colobanthus quitensis).[111] Because of increased temperature, the two vascular plants have increased in population size and in their expansion range. Climate change may also have significant effects on indirect processes, for example soil nutrient availability, plant nutrient uptake, and metabolism.

Increased photosynthesis has also been found in the three continental mosses Bryum argenteum, Bryum pseudotriquetrum, and Ceratodon purpureus.[112] A drying trend is affecting terrestrial biota in East Antarctica. Drier microclimates have led to a reduction in moss health.[112] Because of acute stress, the moss colour has changed. Due to drought and other stressors, many green mosses have turned red to brown. This indicates a shift away from photosynthesis and growth towards investments in photoprotective pigments. If the environmental conditions improve, the mosses can recover.[112] If photoprotective pigments decline relative to chlorophyll, the stressed mosses will be green again. New healthy moss plants can sprout through moribund turf. At the expense of the endemic species Schistidium antarctici, two desiccation tolerant moss species, Bryum pseudotriquetrum and Ceratodon purpureus, have increased.

Significant changes that affect lichen take place on young moraines, near land recently uncovered as glaciers retreat.[113] The changes in diversity of lichens depends on the humidity of the substrate and on the duration of snow cover. Habitats that reduce the frequency of occurrence[clarification needed] are wet or moist stony soil, rock ledges, moist mosses, and meltwater runnels. Continuous deglaciation has resulted in increased colonization by pioneer lichen species. In the maritime cliff rocks and near large penguin colonies, the smallest changes in the lichen biota have been observed.

The increase in UV-B radiation because of the thinner ozone layer causes damage to cells and photosynthesis. Plants try to defend themselves against the increase in ultraviolet radiation with the help of antioxidants.[114] In UV-B exposed plants, the antioxidative enzymes superoxide dismutase, catalase, and peroxidase are synthesized. The exposed plants also synthesize the non-enzymatic antioxidants ascorbate, carotenoids, and flavonoids. All these antioxidants are also used by humans to protect themselves from the damaging effects of free radicals and reactive oxygen species. Uncertainty[clarification needed] of the changing environmental conditions causes difficulties in adaptation and survival for species in Antarctica.[110] The increase in temperature may lead to invasion of alien species and changes of the ecological communities in the Antarctic ecosystem. Increasing UV-B radiation already has a negative impact on Antarctic flora.[110]

Animals[edit]

Euphasia superba).

The marine food web in Antarctica is characterized by few trophic components[clarification needed]and low prey diversity. The predator-prey dynamics depend on fluctuations in the relative[clarification needed] short food chains. A few key species dominate the marine ecosystems. Antarctic krill (Euphasia superba) and ice krill (Euphasia crystallorophias) are examples of key species.[115] They feed on phytoplankton and are the main food for fish and penguins. These organisms are an essential component in the Antarctic food web. However their numbers are declining over time due to global warming. Their decline has dropped by an alarming 80% since the 1970s. A massive decline in their population could potentially threaten major Antarctic species such as penguins, whales and seals.[116] in the periodicity[clarification needed] of sea ice cycles because of climate change cause mismatches between earlier phytoplankton blooms, krill development, and availability for penguins.[117] The consequences for many penguins are increase in foraging trips and reduced breeding success. Absence of krill leads to increased population fluctuations and diet switches for penguins.

As penguins are highest in the Antarctic food web, they will be severely affected by climate change, but they can respond by acclimation, adaptation, or by range shift.[118] Range shift through dispersal leads to colonization elsewhere, but it leads local extinction.[119] The most important responses to climate change in Antarctica are poleward shifts, expansion, and range contraction.[117] Ice-obligate penguins are the most affected species, but the near threatened and ice-intolerant gentoo penguin (Pygoscelis papua) has been benefitted.[120] In maritime Antarctica the population of gentoo penguins is rapidly increasing. Due to regional climate changes, they have moved southwards. Now they colonise previously inaccessible territories. Gentoo penguins use mosses as nesting material. This nesting behaviour is new for southern penguin colonies in Antarctica. By dispersal and adaptive nesting behaviour, gentoo penguins have been remarkably successful in population growth. At the borders of the current geographic distributions, the most obvious responses to climate change occur. There the most likely response to climate change is range shift, because adaptation and microevolution in penguins are too slow.[citation needed]

Pygoscelis papua).

In birds phenological responses are commonly observed, for example shifts in return to breeding places and timing of egg laying.[121] For penguins shift in penguin phenology in response to prey phenology is important. Often common environmental drivers determine the predator-prey synchrony.[117] Climate driven fluctuations that reduce krill availability also reduce the penguin breeding success. Although gentoo penguins share their prey resource with Adélie penguins (Pygoscelis adeliae) during the breeding season, there is no resource competition between the two species.[119] This implies that current population trends in this region are governed by other factors than competition. The emperor penguin (Aptenodytes forsteri), which has a long breeding season, is constrained in space and time. In the future phenological changes in penguins are likely to be limited by their genotypes. Possible ecological traps might attract ice-intolerant species to ice-free areas without foraging grounds.[122] In the future fitness will decrease if there are no favourable conditions for life cycle events and no adaptive response.

Adélie penguins, a species of penguin found only along the coast of Antarctica, may see nearly one-third of their current population threatened by 2060 with unmitigated climate change.[123] Emperor penguin populations may be at a similar risk, with 80% of populations being at risk of extinction by 2100 with no mitigation. With Paris Agreement temperature goals in place, however, that number may decline to 31% under the 2 °C goal or 19% under the 1.5 °C goal.[124] Warming ocean temperatures have also reduced the amount of krill and copepods in the ocean surrounding Antarctica, which has led to the inability of baleen whales to recover from pre-whaling levels. Without a reversal in temperature increases, baleen whales are likely to be forced to adapt their migratory patterns or face local extinction.[125]

Non-native species[edit]

Tourism in Antarctica has been significantly increasing for the past 2 decades with 74,400 tourists in the summer of 2019/2020.[126] The increased human activity associated with tourism likely means there is increased opportunity for the introduction of non-native species. The potential for introduction of non-native species in an environment with rising temperatures and decreasing ice cover is especially concerning because there is an increased probability that introduced species will thrive. Climate change will likely reduce the survivability for native species, improving the chance that introduced species will thrive due to decreased competition.[127] Policy limiting the number of tourists and the permitted activities on and around the continent which mitigate the introduction of new species and limit the disturbance to native species will[clarification needed] help prevent the introduction and dominance by non-native species.[127] The continued designation of protected areas like Antarctic Specially Protected Areas (ASMA) and Antarctic Specially Managed Areas (ASMA) would be one way to accomplish this.

Direct human role[edit]

The development of Antarctica for the purposes of industry, tourism, or an increase in research facilities may put direct pressure on the continent and threaten its status as largely untouched land.[128] On the other hand, regulated tourism in Antarctica already brings about awareness and fosters the investment and public support needed to preserve Antarctica's distinctive environment,[129] although an unmitigated loss of ice on land and sea could greatly reduce its attractiveness.[130]

Policy can be used to increase climate change resilience through the protection of ecosystems. The Polar Code is an international code abided by ships that operate in Antarctica. This code includes regulations and safety measures that aid this fragile ecosystem. These regulations include operational training and assessments, the control of oil discharge, appropriate sewage disposal, and preventing pollution by toxic liquids. [131] Antarctic Specially Protected Areas (ASPA) and Antarctic Specially Managed Areas (ASMA) are areas of Antarctica that are designated by the Antarctic Treaty for special protection of the flora and fauna.[132] Both ASPAs and ASMAs restrict entry but to different extents, with ASPAs being the highest level of protection. Designation of ASPAs has decreased 84% since the 1980s despite a rapid increase in tourism which may pose additional stress on the natural environment and ecosystems.[110] In order to alleviate the stress on Antarctic ecosystems posed by climate change and furthered by the rapid increase in tourism, much of the scientific community advocates for an increase in protected areas like ASPAs to improve Antarctica's resilience to rising temperatures.[110]

See also[edit]

- West Antarctic ice sheet

- East Antarctic ice sheet

- Antarctic sea ice

- Southern Ocean overturning circulation

- Climate of Antarctica

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67. ^ Jump up to:a b c Schuur, Edward A.G.; Abbott, Benjamin W.; Commane, Roisin; Ernakovich, Jessica; Euskirchen, Eugenie; Hugelius, Gustaf; Grosse, Guido; Jones, Miriam; Koven, Charlie; Leshyk, Victor; Lawrence, David; Loranty, Michael M.; Mauritz, Marguerite; Olefeldt, David; Natali, Susan; Rodenhizer, Heidi; Salmon, Verity; Schädel, Christina; Strauss, Jens; Treat, Claire; Turetsky, Merritt (2022). "Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic". Annual Review of Environment and Resources. 47: 343–371. doi:10.1146/annurev-environ-012220-011847. Medium-range estimates of Arctic carbon emissions could result from moderate climate emission mitigation policies that keep global warming below 3°C (e.g., RCP4.5). This global warming level most closely matches country emissions reduction pledges made for the Paris Climate Agreement...