Sea ice is frozen seawater that floats on the ocean, and measuring how thick it is turns out to be hard. As of November 2026, scientists measure sea ice thickness with several methods: surface measurements, submarine surveys, satellites and aircraft, and computer models. No current technology measures thickness directly and continuously over a broad area. Freshly formed sea ice can be as thin as a few sheets of paper, and sea ice can be as thick as a one-story house, depending on how long it has existed. 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 as floes collide.

Each method has its own history. US Navy submarines have collected sonar data on Arctic sea ice since 1958. Sonar sends a sound pulse through the water, and the time the echo takes to return gives the distance to the ice above. Satellites such as CryoSat-2 and NASA's ICESat use altimeters to measure the height of sea ice, from which scientists estimate thickness. ICESat used a laser altimeter from 2003 to 2009, and as of November 2026, altimeter records of sea ice height reach back only to the early 2000s.

Temperature on land is easier to describe than to measure. As of November 2026, 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. Antarctic snowfall averages about 150 millimeters of water per year over the whole continent. The high plateau gets less than 50 millimeters, and some coastal areas get over 200 millimeters, which is why much of Antarctica is a desert.

Beneath the ice, the continent has two parts. The Transantarctic Mountains run across Antarctica and divide it into East and West. Lesser (West) Antarctica is made of younger volcanic and sedimentary rock, while Greater (East) Antarctica is made of older igneous and metamorphic rock. Less than 1 percent of Antarctica is free of ice. It has towering mountain ranges, ice-free dry valleys with ancient rocks and fossils, and active volcanoes. Katabatic winds start when cold, dense air over the high Antarctic ice flows downhill, and they blow hard near the coast.

Life is measured too, though not easily. Antarctic krill can survive up to 200 days without food in winter, shrinking in length as they starve. Young krill eat algae growing on the underside of the sea ice. Krill swarms can be as dense as 30,000 animals per cubic meter, and scientists are still working out how swarms are organized. Seals are hard to study. 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. Seals shed their fur each year, so each tag lasts only until the molt.

Above all of this, the sky glows. Auroras happen when the solar wind meets Earth's magnetic field. Most solar wind is blocked by the magnetosphere, but some ions are briefly trapped around the planet. The northern lights are called aurora borealis, and the southern lights are called aurora australis. Auroras are visible almost every night near the Arctic and Antarctic Circles.

Words to know

• altimeter: height gauge
• sonar: sound ranging
• aurora: sky lights
• magnetosphere: magnetic bubble