polar cap

Polar Ice Cap on Mars, seen by the Hubble Telescope

A polar ice cap is a high latitude region of a planet or natural satellite that is covered in ice.^[1] There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of solid phase matter in the polar region. This causes the term 'polar ice cap' to be somewhat of a misnomer, as the term ice cap itself is applied with greater scrutiny as such bodies must be found over land, and possess a surface area of less than 50,000 km²: larger bodies are referred to as ice sheets.

The composition of the ice will vary. For example Earth's polar ice caps are mainly water ice, while Mars's polar ice caps are a mixture of solid phase carbon dioxide and water ice.

Polar ice caps form because high latitude regions receive less energy in the form of solar radiation from the sun than equatorial regions, resulting in lower surface temperatures.

The Earth's polar ice caps have changed dramatically over the last 12,000 years. Seasonal variations of the ice caps takes place due to varied solar energy absorption as the planet or moon revolves around the sun. Additionally, in geologic time scales, the ice caps may grow or shrink due to climate variation. See ice age, polar climate.

Earth

Extent of the Arctic ice-pack in September, 1978-2002

Extent of the Arctic ice-pack in February, 1978-2002

Earth as seen from Apollo 17, with southern polar ice cap visible (Courtesy NASA)

North Pole

Earth's north pole is covered by floating pack ice (sea ice) over the Arctic Ocean. Portions of the ice that don't melt seasonally can get very thick, up to 3–4 meters thick over large areas, with ridges up to 20 meters thick. One-year ice is usually about a meter thick. The area covered by sea ice ranges between 9 and 12 million km². In addition, the Greenland ice sheet covers about 1.71 million km² and contains about 2.6 million km³ of ice.^[2]

While the International Panel on Climate Change 2001 report predicted that the North polar ice cap would last to 2100 in spite of global warming caused by climate change, the dramatic reduction in the size of the ice cap during the northern summer of 2007 has led some scientists to estimate that there will be no ice at the North Pole by 2030 with devastating effects on the environment.^[3]

Other scientists such as Wieslaw Maslowski, a professor at the Naval Postgraduate School, estimate that there will be no summer ice by as soon as 2013. He argues that this projection is already too conservative as his dataset did not include the minima of 2005 and 2007.^[4]

South Pole

A satellite composite image of Antarctica

The land mass of the Earth's south pole, in Antarctica, is covered by the Antarctic ice sheet. It covers an area of almost 14 million km² and contains 25-30 million km³ of ice. Around 70% of the fresh water on the Earth is held in this ice sheet. See Climate of Antarctica.

Mars

Mars's north polar region with ice cap, composite of Viking 1 orbiter images (Courtesy NASA/JPL-Caltech)

The planet Mars also has polar ice caps, but they consist of frozen carbon dioxide as well as water. The ice caps change with the Martian seasons-the carbon dioxide ice sublimes in summer, uncovering a surface of layered rocks, and then reforms in winter.

Data collected in 2005 from NASA missions to Mars show that the carbon dioxide "ice caps" are melting. The most widely accepted explanation is that fluctuations in the planet's orbit are causing the changes.^[5]

See also

• Polar ice packs
• Ice cap
• Cryosphere

References