Query: Maximum warming occurs over the surface during winter while less surface warming is found in summer when heat is being used to melt sea ice.

Relevant passages:
Climate of the Arctic <=SEP=> The climate of the Arctic is characterized by long , cold winters and short , cool summers . There is a large amount of variability in climate across the Arctic , but all regions experience extremes of solar radiation in both summer and winter . Some parts of the Arctic are covered by ice ( sea ice , glacial ice , or snow ) year-round , and nearly all parts of the Arctic experience long periods with some form of ice on the surface . Average January temperatures range from about − 34 ° C to 0 ° C ( − 40 to +32 ° F ) , and winter temperatures can drop below − 50 ° C ( − 58 ° F ) over large parts of the Arctic . Average July temperatures range from about − 10 to +10 ° C ( 14 to 50 ° F ) , with some land areas occasionally exceeding 30 ° C ( 86 ° F ) in summer .   The Arctic consists of ocean that is largely surrounded by land . As such , the climate of much of the Arctic is moderated by the ocean water , which can never have a temperature below − 2 ° C ( 28 ° F ) . In winter , this relatively warm water , even though covered by the polar ice pack , keeps the North Pole from being the coldest place in the Northern Hemisphere , and it is also part of the reason that Antarctica is so much colder than the Arctic . In summer , the presence of the nearby water keeps coastal areas from warming as much as they might otherwise .

Ice age <=SEP=> An ice age is a period of long-term reduction in the temperature of Earth 's surface and atmosphere , resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers . Within a long-term ice age , individual pulses of cold climate are termed `` glacial periods '' ( or alternatively `` glacials '' or `` glaciations '' or colloquially as `` ice age '' ) , and intermittent warm periods are called `` interglacials '' . In the terminology of glaciology , ice age implies the presence of extensive ice sheets in both northern and southern hemispheres . By this definition , we are in an interglacial period -- the Holocene -- of the ice age . The ice age began 2.6 million years ago at the start of the Pleistocene epoch , because the Greenland , Arctic , and Antarctic ice sheets still exist .

Sea ice <=SEP=> Sea ice arises as seawater freezes . Because ice is less dense than water , it floats on the ocean 's surface ( as does fresh water ice , which has an even lower density ) . Sea ice covers about 7 % of the Earth 's surface and about 12 % of the world 's oceans . Much of the world 's sea ice is enclosed within the polar ice packs in the Earth 's polar regions : the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean . Polar packs undergo a significant yearly cycling in surface extent , a natural process upon which depends the Arctic ecology , including the ocean 's ecosystems . Due to the action of winds , currents and temperature fluctuations , sea ice is very dynamic , leading to a wide variety of ice types and features . Sea ice may be contrasted with icebergs , which are chunks of ice shelves or glaciers that calve into the ocean . Depending on location , sea ice expanses may also incorporate icebergs .

Cryosphere <=SEP=> The cryosphere ( from the Greek κρύος kryos , `` cold '' , `` frost '' or `` ice '' and σφαῖρα sphaira , `` globe , ball '' ) is those portions of Earth 's surface where water is in solid form , including sea ice , lake ice , river ice , snow cover , glaciers , ice caps , ice sheets , and frozen ground ( which includes permafrost ) . Thus , there is a wide overlap with the hydrosphere . The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes , clouds , precipitation , hydrology , atmospheric and oceanic circulation . Through these feedback processes , the cryosphere plays a significant role in the global climate and in climate model response to global changes . The term deglaciation describes the retreat of cryospheric features . Cryology is the study of cryospheres .