Editing Polar ice cap (section)

===North Polar ice cap melting===
{{see also|Arctic sea ice decline}}
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&nbsp;million km<sup>2</sup>. In addition, the [[Greenland ice sheet]] covers about 1.71&nbsp;million km<sup>2</sup> and contains about 2.6&nbsp;million km<sup>3</sup> of ice. When the ice breaks off (calves) it forms icebergs scattered around the northern Atlantic.<ref>{{cite web
|url=http://nsidc.org/news/press/2007_seaiceminimum/20070810_index.html
|title=NSIDC Arctic Sea Ice News Fall 2007
|publisher=nsidc.org
|access-date=27 March 2008
|archive-date=19 April 2014
|archive-url=https://web.archive.org/web/20140419123057/http://nsidc.org/news/press/2007_seaiceminimum/20070810_index.html
|url-status=dead
}}</ref>

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.<ref>
{{cite web
|url=http://nsidc.org/arcticseaicenews/
|title=Arctic Sea Ice News & Analysis
|publisher=National Snow and Ice Data Center
|access-date=9 May 2010
}}
</ref>  Still, between these same years, the overall average ice coverage appears to have declined from 8&nbsp;million km<sup>2</sup> to 5&nbsp;million km<sup>2</sup>.