File:North pole september ice-pack 1978-2002.png|Extent of the Arctic sea-ice in September 1978 – 2002 File:North pole february ice-pack 1978-2002.png|Extent of the Arctic sea-ice in February 1978 – 2002 File:The Blue Marble, AS17-148-22727.jpg|
The Blue Marble, Earth as seen from
Apollo 17 with the southern polar ice cap visible (courtesy
NASA)
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. 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. Still, between these same years, the overall average ice coverage appears to have declined from 8 million km2 to 5 million km2.
South Pole 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).
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 (NSIDC). 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. 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." Polar ice caps have been used to track current climate patterns but also patterns over the past several thousands years from the traces of and 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. 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." 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". 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. ==Mars==