The Arctic is the area around the North Pole, at the top of the Earth, but scientists draw its edge in more than one way. Most scientists define the Arctic as the area inside the Arctic Circle, a line of latitude at about 66.5 degrees north, which holds the Arctic Ocean basin and the northern parts of Scandinavia, Russia, Canada, Greenland, Iceland and Alaska. Some scientists define it instead as the area north of the tree line, where the landscape is frozen and dotted with shrubs and lichens, and the tree line broadly matches where the average July temperature stays at or below 10 degrees Celsius (50 degrees Fahrenheit). Most of the Arctic is ocean, and the Arctic Ocean is bordered by Greenland, Canada, Norway, Alaska and Russia.
Antarctica is a continent, and a huge sheet of ice covers it. The water around it is the Southern Ocean, which the United States recognizes as reaching from the Antarctic coast to 60 degrees South, although not all countries agree on its edge. The Antarctic Convergence, an uneven line where cold water flowing north from Antarctica meets the warmer waters of the world's oceans, marks the edge of the Antarctic region.
A glacier is a slow-moving river of ice. An ice sheet is a mass of glacial land ice larger than 50,000 square kilometers, and Earth has just two: one covering most of Greenland and one across Antarctica. As of November 2026, the Antarctic Ice Sheet is the largest single mass of ice on Earth, covering almost 14 million square kilometers, about the area of the lower 48 states and Mexico together. The Greenland Ice Sheet covers about 1.7 million square kilometers, 80 percent of Greenland, the world's largest island. The Transantarctic Mountains divide Antarctica into East and West. East Antarctica's ice is thicker and rests on rock that is mostly above the ocean surface, while in the west the ice is thinner and much of the rock beneath it lies below the ocean surface. Less than 1 percent of Antarctica is free of ice, yet it has towering mountain ranges, ice-free dry valleys with ancient rocks and fossils, and active volcanoes.
Ice sheets are not still, even though they look frozen in place. Near the top of an ice sheet, where the slope is shallowest, ice moves a few centimeters to a few meters per year, while near the coast, ice flowing into outlet glaciers can move hundreds of meters or even several kilometers per year. Rapidly moving ice streams make up about 10 percent of the Antarctic Ice Sheet, and most of the ice leaving the continent flows through them, with some moving more than 1,000 meters per year. Ice shelves are floating sheets of ice that are connected to the land. The British Antarctic Survey released a map of the land beneath the Antarctic Ice Sheet in 2001 and updated it in 2013, because knowing the shape of the bedrock helps scientists understand how the ice moves.
As of November 2026, the Arctic Ocean is the smallest of the world's five ocean basins, at about 14 million square kilometers (5.4 million square miles). It is also the shallowest of the five and the least salty, because of low evaporation and large amounts of fresh water from rivers and glaciers. Its deepest part, the Canada Basin, reaches 5,441 meters (17,850 feet), and year-round ice cover has made the Arctic Ocean isolated and little explored.
Ice also preserves a chronological record. Each year a new layer of snow falls on the ice sheets of Greenland and Antarctica, and because summer snow differs from winter snow in chemistry and texture, each layer records that year. As snow falls it traps dust, volcanic ash, smoke and pollen, and what is trapped tells scientists about the conditions when the snow formed. Scientists drill long cores out of ice sheets, some more than 3,500 meters (11,000 feet) deep, and they hold hundreds of thousands of years of snow layers. Drilling of long ice cores began in Greenland and Antarctica in the late 1960s. By the early 1990s the Greenland project had pulled a core of 3,053.44 meters, covering at least 110,000 years, and Antarctic cores reach back about 750,000 years. Scientists additionally lower a thermometer into the borehole left by a core to measure the temperature of the ice sheet directly, because snow and ice, like an insulated thermos, preserve the temperature of each layer.
Sea ice is frozen seawater that floats on the ocean, and it behaves differently from the land ice of an ice sheet. Arctic and Antarctic sea ice differ mainly because of their different geographies: the Arctic is a semi-enclosed ocean almost completely surrounded by land, and Antarctica is a continent surrounded by ocean. In late winter Arctic sea ice covers on average about 15.5 million square kilometers and Antarctic sea ice about 18.5 million. By summer's end Antarctic sea ice falls to about 2.5 million square kilometers, and Arctic sea ice to about 6.5 million (1981 to 2010 average). As of November 2026, Antarctic sea ice is typically 1 to 2 meters thick, while Arctic sea ice is typically 2 to 3 meters thick, because Arctic ice stays in the cold basin and piles into ridges. Measuring the thickness of sea ice is surprisingly difficult. As of November 2026, scientists use surface measurements, submarine surveys, satellites and aircraft, and computer models, and no current technology measures thickness directly and continuously over a broad area. US Navy submarines have collected sonar data on Arctic sea ice since 1958, and sonar works by sending a sound pulse through the water and timing the echo that returns from the ice above. Satellites such as CryoSat-2 and NASA's ICESat use altimeters, instruments that measure the height of sea ice, from which scientists estimate thickness.
Temperatures and precipitation at the poles differ considerably from place to place. In the interior of Antarctica winter temperatures fall below -60 degrees Celsius, and summers rarely exceed -20. Along the coast, winter months average -10 to -30 and the summer is near freezing. A satellite-based measurement in 2010 recorded -93.2 degrees Celsius (-135.8 degrees Fahrenheit) in Antarctica, lower than the -89.2 degrees measured by thermometer at Vostok in 1983. These figures are as of November 2026. Antarctic snowfall averages about 150 millimeters of water per year over the whole continent, with less than 50 millimeters on the high plateau and over 200 millimeters in some coastal areas, so much of Antarctica is a desert. Katabatic winds start when cold, dense air over the high Antarctic ice flows downhill, and they blow hard near the coast. The Arctic has two main climate types: near the ocean the climate is maritime, with stormy, wet winters, and inland it is continental, drier, with winters that can be severe and summers that can be very warm.
Life in the Antarctic region survives the extreme conditions in several remarkable ways. Antarctic fish have natural antifreeze in their blood, called glycoproteins, that stops it from freezing, and the icefish has no red blood cells and carries oxygen in its blood plasma. Emperor penguins keep warm in several ways: their layered, scale-like feathers shrug off winds over about 110 kilometers per hour, and they have small bills and flippers and blood vessels that warm and cool blood to save heat. Emperor penguin fathers keep the single egg warm on their feet for about two months, without eating. Weddell seals live under the ice and breathe through holes, and in winter they use their teeth to rasp the new ice and keep the holes open, which wears the teeth down. They can dive for up to 45 minutes and as deep as 720 meters.
Antarctic krill can survive up to 200 days without food in winter, shrinking in length as they starve. Crabeater, Ross and leopard seals breed on the ice in a different place each time, so biologists attach radio transmitters that send signals by satellite, and because seals shed their fur each year, each tag lasts only until the molt. Scientists on Adelie penguin colonies near Casey research station have been counting penguins using photos taken by helicopter and by automatic cameras that watch nests all year round. The Australian Antarctic Division has the only research lab in the world where the entire life cycle of Antarctic krill can be studied. As of November 2026, eggs there sink about 1,000 meters before hatching, and the larvae swim back up toward the surface.
The Arctic supports a different community of animals. Arctic foxes have white winter coats that help them blend into snow and ice, and in summer the coat turns brown or gray, which helps them hide among the rocks and plants. A snowy owl may eat more than 1,600 lemmings a year, which is three to five every day, and how many lemmings there are may decide how far south the owls travel. Musk oxen have long guard hairs over a shorter undercoat that adds warmth in winter, and when threatened by wolves, a herd forms a ring with the young in the middle and the horns facing outward. Caribou and reindeer are the same species, Rangifer tarandus: caribou are native to North America, and reindeer are native to northern Europe and Asia. Walruses use their long tusks to haul their bodies out of the water and to break breathing holes in the ice from below, and both males and females have tusks, which are large canine teeth that keep growing all their lives. As of November 2026, Arctic terns hold the record for the longest migration of any animal, flying each year from the Arctic to the Antarctic.
The Inuit of Canada and Greenland built snow houses, known as igloos, from stacked blocks of ice insulated with snow. Blocks were stacked in a spiral to make a dome, and an igloo could hold from two to 20 people. The Sami of northern Scandinavia and the Nenets of Russia's Arctic herd reindeer and use them for meat. Nunavut, Canada's largest territory, was created in 1999 after an agreement between the government of Canada and Inuit bands. As of November 2026, more than half of its people identify as Inuit, and Inuktitut is the most-spoken language.
Place names in Antarctica are chosen by international committees, and the names often honor discoverers, ships or events, or describe a feature, such as Fishhook Ridge, named for its shape.
As of November 2026, NSF Amundsen-Scott South Pole Station is the southernmost year-round research station in the world. It opened in 1956 for the International Geophysical Year, and the current elevated station was completed in 2008. It hosts the South Pole Telescope and the IceCube neutrino detector, built in the ice. Its clear, dry air and lack of light pollution suit astronomy. The station drifts about 10 meters each year because the ice it sits on moves. Halley Research Station, on the moving Brunt Ice Shelf, was designed to move with the ice, and scientists there helped discover the ozone hole, a seasonal thinning of the ozone layer. Roald Amundsen was the first to reach the South Pole, in December 1911, and Robert F. Scott arrived in January 1912, and the station is named for both men.
Antarctica has no native people. The Antarctic Treaty was signed in 1959 by 12 countries, and it freezes territorial claims, so no new claims can be made while it is in force. Seven countries have territorial claims in Antarctica: Argentina, Australia, Chile, France, New Zealand, Norway and the United Kingdom. Some claims overlap, and other countries do not recognize any claims. The Treaty entered into force in 1961. Antarctica is a demilitarised zone, and the 1959 treaty prohibits military activities, weapons testing and the disposal of radioactive waste south of 60 degrees South. Scientific observations and results from Antarctica must be exchanged and made freely available, and all stations, installations and equipment are open to inspection at all times. Beyond the 1959 treaty are two main agreements: CCAMLR, which protects the marine life of the Southern Ocean, and the Madrid Protocol, which bans mining except for science and requires environmental impact assessments. The Antarctic Treaty sets Antarctica aside for peaceful science.
Words to know
- latitude: distance from equator
- molt: shed fur
- demilitarised: free of military
- glycoproteins: antifreeze molecules
