Despite its isolation, Antarctica has experienced warming and ice loss in recent decades, driven by greenhouse gas emissions. West Antarctica warmed by over 0.1 °C per decade from the 1950s to the 2000s, and the exposed Antarctic Peninsula has warmed by since the mid-20th century. The colder, stabler East Antarctica did not show any warming until the 2000s. Around Antarctica, the Southern Ocean has absorbed more oceanic heat than any other ocean, and has seen strong warming at depths below . Around the West Antarctic, the ocean has warmed by since 1955.
The warming of the Southern Ocean around Antarctica has caused the weakening or collapse of ice shelves, which float just offshore of glaciers and stabilize them. Many coastal glaciers have been losing mass and retreating, causing net ice loss across Antarctica although the East Antarctic ice sheet continues to gain ice inland. By 2100, net ice loss from Antarctica is expected to add about to global sea level rise. Marine ice sheet instability may cause West Antarctica to contribute tens of centimeters more if it is triggered before 2100. With higher warming, instability would be much more likely and could double the 21st-century global sea level rise.
The fresh meltwater from the ice dilutes the saline Antarctic bottom water weakening the lower cell of the Southern Ocean overturning circulation (SOOC). According to some research, a full collapse of the SOOC may occur at between and of global warming although the full effects are expected to occur over multiple centuries. They include less precipitation in the Southern Hemisphere but more in the Northern Hemisphere, an eventual decline of fisheries in the Southern Ocean and a potential collapse of certain marine ecosystems. While many Antarctic species remain undiscovered, there are documented increases in Antarctic flora, and large fauna such as penguins are already having difficulty retaining suitable habitat. On ice-free land, permafrost thaws release greenhouse gases and formerly frozen pollution. Antarctic warming and associated changes in Southern Ocean circulation can also influence climate patterns in parts of Africa, affecting regional rainfall and temperature variability.
The West Antarctic ice sheet is likely to melt completely unless temperatures are reduced by below 2020 levels. The loss of that ice sheet would take between 500 and 13,000 years. A sea level rise of would occur if the ice sheet collapses, which would leave ice caps on the mountains, and a rise of would occur if those ice caps also melt. The far more stable East Antarctic ice sheet may cause a sea level rise of only to from the current level of warming, a small fraction of the contained in the full ice sheet. With global warming being around , vulnerable areas like Wilkes Basin and Aurora Basin may collapse over around 2,000 years, potentially adding up to to sea levels.
Temperature and weather changes
Antarctica is the coldest, driest continent on Earth, and has the highest average elevation. Antarctica's dryness means the air contains little water vapor and conducts heat poorly. The Southern Ocean surrounding the continent is far more effective at absorbing heat than any other ocean. The presence of extensive, year-round sea ice, which has a high albedo (reflectivity), adds to the albedo of the ice sheets' own bright, white surface. Antarctica's coldness makes it the only place on Earth to have an atmospheric temperature inversion occur every winter. Elsewhere on Earth, the atmosphere is at its warmest near the surface and becomes cooler as elevation increases.
During the Antarctic winter, the surface of central Antarctica becomes cooler than middle layers of the atmosphere, which makes greenhouse gases trap heat in the middle atmosphere, and reduce its flow toward the surface and toward space, rather than preventing the flow of heat from the lower atmosphere to the upper layers. The effect lasts until the end of the Antarctic winter. Early climate models predicted temperature trends over Antarctica would emerge more slowly and be more subtle than those elsewhere.
There were fewer than twenty permanent weather stations across the continent and only two in the continent's interior. Automatic weather stations were deployed relatively late, and their observational record was brief for much of the 20th century satellite temperature measurements began in 1981 and are typically limited to cloud-free conditions. Thus, datasets representing the entire continent had begun to appear only by the very end of the 20th century. The exception was the Antarctic Peninsula, where warming was pronounced and well-documented. It was eventually found to have warmed by since the mid 20th century.
Based on those limited data, several papers published in the early 2000s said there had been an overall cooling over continental Antarctica outside the Peninsula. PDF available at AMS Online PDF available at Annular Modes Website In particular, a 2002 analysis led by Peter Doran indicated stronger cooling than warming over Antarctica between 1966 and 2000, and found the McMurdo Dry Valleys in East Antarctica had experienced cooling of 0.7 °C per decade. The paper noted that its data was limited, and it still found warming over 42% of the continent.
The paper received widespread media coverage, as multiple journalists described those findings as "contradictory" to global warming, which was criticized by scientists at the time. The "controversy" around the cooling of Antarctica received further attention in 2004 when Michael Crichton wrote the novel State of Fear. The novel featured a fictional conspiracy among climate scientists to fake evidence of global warming, and cited Doran's study as proof that there was no warming in Antarctica outside of the Peninsula. First Edition That novel was mentioned in a 2006 US Senate hearing in support of climate change denial, and Peter Doran published a statement in The New York Times decrying the misinterpretation of his work. The British Antarctic Survey and NASA also issued statements affirming the strength of climate science after the hearing. NASA image by Robert Simmon, based on data from Joey Comiso, GSFC.
By 2009, researchers had combined historical weather-station data with satellite measurements to create consistent temperature records going back to 1957 that demonstrated warming of >0.05 °C per decade across the continent, with cooling in East Antarctica offset by the average temperature increase of at least 0.176 ± 0.06 °C per decade in West Antarctica. That paper was widely reported on, and subsequent research confirmed clear warming over West Antarctica in the 20th century, the only uncertainty being the magnitude.
During 2012–2013, estimates based on WAIS Divide ice cores and revised temperature records from Byrd Station suggested a much-larger West-Antarctica warming of since 1958, or around per decade, but some scientists continued to emphasize uncertainty. In 2022, a study narrowed the warming of the Central area of the West Antarctic Ice Sheet between 1959 and 2000 to per decade, and conclusively attributed it to increases in greenhouse gas concentrations caused by human activity. Likewise, the strong cooling at McMurdo Dry Valleys was confirmed to be a local trend.
The Antarctica-wide warming trend continued after 2000, and in February 2020, the continent recorded its highest-ever temperature of 18.3 °C, exceeding the previous record of 17.5 °C in March 2015. The East Antarctica interior also demonstrated clear warming between 2000 and 2020. 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.
Changes in atmospheric circulation patterns like the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) slowed or partially reversed the warming of West Antarctica, with the Antarctic Peninsula experiencing cooling from 2002. While a variability in those patterns is natural, past ozone depletion had also led the SAM to be stronger than it had been in the past 600 years of observations. Starting around 2002, studies predicted a reversal in the SAM once the ozone layer began to recover following the Montreal Protocol, and those changes are consistent with their predictions.Meredith, M.; Sommerkorn, M.; Cassotta, S; Derksen, C.; et al. (2019). "Chapter 3: Polar Regions" (PDF). IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. p. 212.
Under the most intense climate change scenario, known as RCP8.5, models predict Antarctic surface temperatures to rise by by 2070 and by on average by 2100, which will be accompanied by a 30% increase in precipitation and a 30% decrease in sea ice by 2100. The Southern Ocean waters "south of 50° S latitude would also warm by about by 2070. RCPs were developed in the late 2000s, and early 2020s research considers RCP8.5 much less likely than the more-moderate scenarios like RCP 4.5, which lie in between the worst-case scenario and the Paris Agreement goals. If a low-emission scenario mostly consistent with the Paris Agreement goals is followed, then Antarctica would experience surface and ocean warming of less than by 2070, while less than 15% of sea ice would be lost and precipitation would increase by less than 10%.
Effects on ocean currents
Between 1971 and 2018, over 90% of thermal energy from global heating entered the oceans. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License The Southern Ocean absorbs the most heat; after 2005, it accounted for between 67% and 98% of all heat entering the oceans. The temperature in the ocean's upper layer in West Antarctica has warmed by since 1955, and the Antarctic Circumpolar Current (ACC) is also warming faster than the average. It is also a highly important carbon sink. Those properties are connected to the Southern Ocean overturning circulation (SOOC), one half of the global thermohaline circulation. As such, estimates on when global warming will reach – inevitable in all scenarios where greenhouse gas emissions have not been significantly lowered – depend on the strength of the circulation more than any factor other than the overall emissions.
The overturning circulation has two parts; the smaller upper cell, which is most-strongly affected by winds and precipitation, and the larger lower cell that is defined by the temperature and salinity of Antarctic bottom water. Since the 1970s, the upper cell has strengthened by 50–60%, and the lower cell has weakened by 10–20%. The natural cycle of the Interdecadal Pacific Oscillation (IPO) contributed to some of the change, but climate change has also played a clear role by shifting the Southern Annular Mode (SAM) pattern, which alters winds and precipitation.
Fresh meltwater from the erosion of the West Antarctic ice sheet dilutes the more-saline Antarctic bottom water, which flows at a rate of 1100–1500 billion tons (GT) per year. During the 2010s, a temporary reduction in ice-shelf melting in West Antarctica allowed for the partial recovery of Antarctic bottom water and the lower cell of the circulation. Greater melting and further decline of the circulation is expected in the future.