Аннотация За период спутниковых наблюдений (1979–2020 гг.) происходит постоянное уменьшение площадилетних льдов и их толщины со скоростью 13 и 15% за 10 лет соответственно. Отмечается быстроесокращение площади льдов старше четырёх лет и увеличение площади однолетних льдов. Анализданных о состоянии морских льдов в Арктике за голоцен, за тёплую стадию последнего межледни-ковья и середину плиоцена показал, что в тёплые эпохи прошлого площадь летних льдов сокраща-лась до минимальных значений. Эмпирические данные и результаты моделирования показывают,что в настоящее время запущен механизм замещения многолетних льдов сезонными, что являетсяестественным состоянием перехода от этапа преобладания сезонных льдов к безлёдной Арктики.Основной драйвер современного сокращения морских льдов – рост содержания СО2. Если кон-центрация СО2 в атмосфере будет увеличиваться, то может сработать один из сценариев, имевшийместо в прошлом. Summary Data from satellite observations (1979–2020) showed, that over the last 40 years the years with a decrease in the area ofsummer ice extent and their thickness have prevail. Over 10 years, negative trends in anomalies of ice area and thicknessof the ice are −13 and −15%, respectively. There is also a rapid reduction in the area of old ice (> 4 year-old):while in 1985 it was estimated at 2.7 million km2 while in March 2010 it was 0.34 million km2. The paper analysespaleo-sea ice extent during the Holocene (the last 12,000 years) based on empirical biomarkers IP25 (a sea ice proxywith 25 carbon atoms synthesized by the specific Arctic sea ice diatoms Haslea spp. which have been proven to bea suitable proxy for paleo-sea ice reconstructions) obtained from deep-sea cores from the North Atlantic. The dataobtained showed that during the warm periods of the Early and Middle Holocene, the area of summer sea ice wasreduced to a minimum. This confirms the conclusion made earlier in [28] that the current trend of reducing the areaand thickness of ice is unprecedented over the past 1,500 years. There is no complete analogue of the climate in thepast corresponding to the current level of the CO2 concentration in the atmosphere. The closest time interval in termsof CO2 content is the warming of the Middle Pliocene between 3 and 4 million years ago, when the CO2 content inthe atmosphere was 450–500 ppm against approximately 420 ppm at present. Paleo-climate reconstructions for thisperiod estimate the global temperature to be 3.0–3.5±0.5 °C higher than at the end of the 19th century. Summer airtemperatures in the high latitudes of the Northern Hemisphere exceeded the current ones by 8–10 °C, and the seaice in the Arctic shelf seas was completely absent in the summer. Empirical data and model simulations have shownthat presently the main driver of the reduction of the Arctic sea ice area is the increase in concentration of CO2 in theatmosphere. At the present time old sea ice tends to be replaced by seasonal ice demonstrating natural shift from predominanceof permanent ice to the ice-free Arctic. In case of continuous increase in CO2 concentration in the atmospheredespite the emission control measures, one of the scenarios, which had happened in the past, may come true.
