Polar ice cap

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Polar ice cap on Mars, seen by the Hubble Space Telescope Mars, as seen by the Hubble Telescope.jpg
Polar ice cap on Mars, seen by the Hubble Space Telescope

A polar ice cap or polar cap is a high-latitude region of a planet, dwarf 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, but only that it must be a body of solid phase matter in the polar region. This causes the term "polar ice cap" to be something of a misnomer, as the term ice cap itself is applied more narrowly to bodies that are over land, and cover 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 caps are mainly water ice, whereas Mars's polar ice caps are a mixture of solid 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.

Earth's polar 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 change.


North Polar ice cap melting

Earth's North Pole is covered by floating pack ice (sea ice) over the Arctic Ocean. Portions of the ice that do not 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 1 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. When the ice breaks off (calves) it forms icebergs scattered around the northern Atlantic. [2]

According to the National Snow and Ice Data Center, "since 1979, winter Arctic ice extent has decreased about 4.2 percent per decade". Both 2008 and 2009 had a minimum Arctic sea ice extent somewhat above that of 2007. At other times of the year the ice extent is still sometimes near the 1979–2000 average, as in April 2010, by the data from the National Snow and Ice Data Center. [3] Still, between these same years, the overall average ice coverage appears to have declined from 8 million km2 to 5 million km2.

South Pole

A satellite composite image of Antarctica Antarctica 6400px from Blue Marble.jpg
A satellite composite image of Antarctica

Earth's south polar land mass, Antarctica, is covered by the Antarctic ice sheet. It covers an area of about 14.6 million km2 and contains between 25 and 30 million km3 of ice. Around 70% of the fresh water on Earth is contained in this ice sheet.

Data from the National Snow and Ice Data Center shows that the sea ice coverage of Antarctica has a slightly positive trend over the last three decades (1979–2009). [4]

Historical cases

Over the past several decades, Earth's polar ice caps have gained significant attention because of the alarming decrease in land and sea ice. NASA reports that since the late 1970s, the Arctic has lost an average of 20,800 square miles (53,900 square kilometres) of sea ice per year while the Antarctic has gained an average of 7,300 square miles (18,900 km2) of sea ice per year. At the same time, the Arctic has been losing around 50 cubic kilometres (gigatons) of land ice per year, almost entirely from Greenland's 2.6 million gigaton sheet. On 19 September 2014, for the first time since 1979, Antarctic sea ice extent exceeded 7.72 million square miles (20 million square kilometres), according to the National Snow and Ice Data Center. The ice extent stayed above this benchmark extent for several days. The average maximum extent between 1981 and 2010 was 7.23 million square miles (18.72 million square kilometres). The single-day maximum extent in 2014 was reached on 20 Sep, according to NSIDC data, when the sea ice covered 7.78 million square miles (20.14 million square kilometres). The 2014 five-day average maximum was reached on 22 Sep, when sea ice covered 7.76 million square miles (20.11 million square kilometres), according to NSIDC. [5] This increase could be due to the reduction in the salinity of the Antarctic Ocean as a result of the previous melting of the ice sheet, by increasing the freezing point of the seawater.

The current rate of decline of the ice caps has caused many investigations and discoveries on glacier dynamics and their influence on the world's climate. In the early 1950s, scientists and engineers from the US Army began drilling into polar ice caps for geological insight. These studies resulted in "nearly forty years of research experience and achievements in deep polar ice core drillings... and established the fundamental drilling technology for retrieving deep ice cores for climatologic archives." [6] Polar ice caps have been used to track current climate patterns but also patterns over the past several thousands years from the traces of CO2 and CH4 found trapped in the ice. In the past decade, polar ice caps have shown their most rapid decline in size with no true sign of recovery. [7] Josefino Comiso, a senior research scientist at NASA, found that the "rate of warming in the Arctic over the last 20 years is eight times the rate of warming over the last 100 years." [8] In September 2012, sea ice reached its smallest size ever. Journalist John Vidal stated that sea ice is "700,000 sq km below the previous minimum of 4.17m sq km set in 2007". [9] In August 2013, Arctic sea ice extent averaged 6.09m km2, which represents 1.13 million km2 below the 1981–2010 average for that month. [10]


Mars's north polar region with ice cap, composite of Viking 1 orbiter images (Courtesy NASA/JPL-Caltech) Mars NPArea-PIA00161.jpg
Mars's north polar region with ice cap, composite of Viking 1 orbiter images (Courtesy NASA/JPL-Caltech)

In addition to Earth, the planet Mars also has polar ice caps. They consist of primarily water-ice with a few percent dust. [11] Frozen carbon dioxide makes up a small permanent portion of the Planum Australe or the South Polar Layered Deposits. In both hemispheres a seasonal carbon dioxide frost deposits in the winter and sublimates during the spring.[ citation needed ]

Data collected in 2001 from NASA missions to Mars show that the southern residual ice cap undergoes sublimation inter-annually. The most widely accepted explanation is that fluctuations in the planet's orbit are causing the changes. [12]


On 29 April 2015, NASA stated that its New Horizons missions had discovered a feature thought to be a polar ice cap on the dwarf planet Pluto. [13] The probe's flyby of Pluto in July 2015 allowed the Alice ultraviolet imaging spectrometer to confirm that the feature was in fact an ice cap composed of methane and nitrogen ices. [14]

A photo describing the frozen methane and nitrogen on Pluto gathered from New Horizons NH-Pluto-MethaneIce-20150715.png
A photo describing the frozen methane and nitrogen on Pluto gathered from New Horizons

See also

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<span class="mw-page-title-main">Cryosphere</span> Those portions of Earths surface where water is in solid form

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<span class="mw-page-title-main">Climate of Antarctica</span> Overview of the climate of Antarctica

The climate of Antarctica is the coldest on Earth. The continent is also extremely dry, averaging 166 mm (6.5 in) of precipitation per year. Snow rarely melts on most parts of the continent, and, after being compressed, becomes the glacier ice that makes up the ice sheet. Weather fronts rarely penetrate far into the continent, because of the katabatic winds. Most of Antarctica has an ice-cap climate with very cold, generally extremely dry weather.

<span class="mw-page-title-main">Sea ice</span> Ice formed from frozen seawater

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<span class="mw-page-title-main">Ice shelf</span> Large floating platform of ice caused by glacier flowing onto ocean surface

An ice shelf is a large floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland, Northern Canada, and the Russian Arctic. The boundary between the floating ice shelf and the anchor ice that feeds it is the grounding line. The thickness of ice shelves can range from about 100 m (330 ft) to 1,000 m (3,300 ft).

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<span class="mw-page-title-main">National Snow and Ice Data Center</span> U.S. information and referral center

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<span class="mw-page-title-main">Antarctic ice sheet</span> Earths southern polar ice cap

The Antarctic ice sheet is one of the two polar ice caps of Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth, with an average thickness of over 2 kilometers. It covers an area of almost 14 million square kilometres and contains 26.5 million cubic kilometres of ice. A cubic kilometer of ice weighs approximately 0.92 metric gigatonnes, meaning that the ice sheet weighs about 24,380,000 gigatonnes. It holds approximately 61% of all fresh water on Earth, equivalent to about 58 meters of sea level rise if all the ice were above sea level. In East Antarctica, the ice sheet rests on a major land mass, while in West Antarctica the bed can extend to more than 2,500 m below sea level.

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<span class="mw-page-title-main">Climate of the Arctic</span> Overview of the climate of the Arctic

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<span class="mw-page-title-main">Arctic Ocean</span> Ocean in the north polar region

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<span class="mw-page-title-main">Arctic sea ice decline</span> Sea ice loss observed in recent decades in the Arctic Ocean

Arctic sea ice decline has occurred in recent decades due to the effects of climate change on oceans, with declines in sea ice area, extent, and volume. Sea ice in the Arctic Ocean has been melting more in summer than it refreezes in the winter. Global warming, caused by greenhouse gas forcing is responsible for the decline in Arctic sea ice. The decline of sea ice in the Arctic has been accelerating during the early twenty‐first century, with a decline rate of minus 4.7% per decade. It is also thought that summertime sea ice will cease to exist sometime during the 21st century. This sea ice loss is one of the main drivers of surface-based Arctic amplification. Sea ice area means the total area covered by ice, whereas sea ice extent is the area of ocean with at least 15% sea ice, while the volume is the total amount of ice in the Arctic.

<span class="mw-page-title-main">Arctic ice pack</span> The sea ice cover of the Arctic Ocean and its vicinity

The Arctic ice pack is the sea ice cover of the Arctic Ocean and its vicinity. The Arctic ice pack undergoes a regular seasonal cycle in which ice melts in spring and summer, reaches a minimum around mid-September, then increases during fall and winter. Summer ice cover in the Arctic is about 50% of winter cover. Some of the ice survives from one year to the next. Currently, 28% of Arctic basin sea ice is multi-year ice, thicker than seasonal ice: up to 3–4 m (9.8–13.1 ft) thick over large areas, with ridges up to 20 m (65.6 ft) thick. The regular seasonal cycle there has been an underlying trend of declining sea ice in the Arctic in recent decades as well.

<span class="mw-page-title-main">Antarctic sea ice</span> Sea ice of the Southern Ocean

Antarctic sea ice is the sea ice of the Southern Ocean. It extends from the far north in the winter and retreats to almost the coastline every summer, getting closer and closer to the coastline every year due to sea ice melting. Sea ice is frozen seawater that is usually less than a few meters thick. This is the opposite of ice shelves, which are formed by glaciers, they float in the sea, and are up to a kilometre thick. There are two subdivisions of sea ice: fast ice, which are attached to land; and ice floes, which are not.


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