As the seasons progress, both land and sea ice melts/shrinks during the long arctic summer, and then begins to grow again by late September. This “cryosphere” reaches its maximum extent around mid-March after which the melt/freeze cycle repeats. For the Southern Hemisphere, the high and low ice extents are of course reversed.
The Arctic (and Antarctic) “ice caps” are an important part of the earth’s self regulated climate control system. The ice surface is highly reflective and “bounces” much of the incoming solar energy back to space. The ice-cooled water of the Arctic Ocean sinks to the sea bottom and spreads southward as an essential part of a huge global heat-transfer loop. Frigid water draining from the Greenland Ice Cap in the summer serves a similar function.
Data from the National Snow and Ice Data Center (NSIDC) as well as many university studies show that arctic ice variation has causes beyond the fixed astronomical one (which we call the seasons).
Second and quite important is the ocean circulation pattern. Warmer water intruding from the south can melt away the underpinning ice, thinning the “pack”. Research has offered good reason to suspect this mechanism for arctic ice melt. Joseph D’Aleo, A Certified Consulting Meteorologist, phrases it this way:
“Warming results in part from the reduction of arctic ice extent because of flows of the warm water associated with the warm phases of the PDO and AMO [The PDO is the Pacific Decadal Oscillation, and the AMO is the Arctic Multi-decadal Oscillation] into the arctic from the Pacific through the Bering Straits and the far North Atlantic and the Norwegian Current”. This can impact land-based ice as well due to warmer air which accompanies the milder current.
There’s a well documented correlation between these shifting ocean circulation patterns and arctic sea ice melt.
Third, wind currents can move the ice over great distances at sea. One can not automatically say a lower oceanic ice cover is because of global warming. Since the measurements of sea ice are taken by satellite, if it is piled up along one end of the ocean basin by a persistent wind current, then this will be interpreted as less ice cover, when in fact the volume of ice may be the same. A statement from the NSIDC supports this fact.
Unusual wind currents have been known to transport very warm air northward even in the dead of winter, eating away at terrestrial ice too.
Fourth of course is the air temperature itself. An unusually warm period will no doubt contribute towards a greater percentage of the total ice loss, while a warm ocean current might count for a greater percentage of the sea ice melt in another year. Arctic ice loss is likely from a combination of all these factors but they are not necessarily of equal weighting.
So, while a warmer climate can certainly contribute to arctic ice loss, it’s inaccurate to offer it up as a lone scapegoat. To do good science here, a closer examination of all these parameters (or any others that may come to light) must be applied in each case.