What is Arctic ice pack?
[[File:Arctic_Ice_Thickness.gif|thumb|[[National Oceanic and Atmospheric Administration|NOAA]] projected Arctic changes.]] [[File:Approaching_the_2011_Arctic_Sea_Ice_Minimum.ogv|thumb|This animation shows the Arctic Ocean melt during the summer of 2011.]] [[File:Link_between_Sea-Ice_Fraction_and_Absorbed_Solar_Radiation_over_the_Arctic_Ocean.ogg|thumb|This visual shows the Arctic sea ice change and the corresponding absorbed solar radiation change during June, July, and August from 2000 through 2014.]] The '''Arctic ice pack''' or '''arctic ice cap''' is an [[ice shield]] covering the [[Arctic Ocean]]. It changes during the year. Usually, the ice melts in spring and summer, and increases during autumn and winter. The minimum cover is around mid-September. Summer ice cover in the [[Arctic]] is about half of winter cover. Some of the ice survives from one year to the next. Currently, 28% of Arctic basin sea ice is [[Sea ice|multi-year ice]]. Multi-year ice is thicker than seasonal ice: up to {{Convert|3|-|4|m|1|abbr=on|sp=us}} thick over large areas, with ridges up to {{Convert|20|m|1|abbr=on|sp=us}} thick. As well as the regular seasonal cycle there has been an underlying trend of declining sea ice in the Arctic in recent decades. == Climatic importance == === Energy balance effects === [[Sea ice]] is important for the heat balance of the polar oceans: it insulates the (relatively) warm ocean from the much colder air above. With ice, less heat is lost from the oceans. Sea ice is highly [[Albedo|reflective of solar radiation]], reflecting about 60% of incoming solar radiation when bare and about 80% when covered with snow. This is due to a feedback known as the [[Albedo|albedo effect]].<ref>{{Cite journal|last1=Huwald|first1=Hendrik|last2=Higgins|first2=Chad W.|last3=Boldi|first3=Marc-Olivier|last4=Bou-Zeid|first4=Elie|last5=Lehning|first5=Michael|last6=Parlange|first6=Marc B.|date=2009-08-01|title=Albedo effect on radiative errors in air temperature measurements|url=http://infoscience.epfl.ch/record/140742|