Arctic & Antarctic
Dramatic melting of sea ice is being observed in the polar oceans. This relatively recent loss of sea ice provides some of the strongest evidence that climate change is under way and that it is accelerating.
Overall Arctic sea ice volume has been decreasing since at least 1980.
NOAA satellite imagery shows that the average winter maximum sea ice surface area has decreased by 2.8% per decade, and the average summer minimum sea ice extent has decreased by 11.1% per decade. If the observed melting continues, the fabled “Northwest Passage” will be a reality in a few years, opening new shipping routes, and facilitating the exploration and extraction of fossil fuels from the Arctic seabed.
Sea ice reflects much of the sun’s energy back into the atmosphere, whereas open ocean water absorbs much of the sun’s heat energy (think of wearing a dark blue shirt verses a bright white shirt on a sunny day – the dark blue will be much hotter!) Although melting sea ice does not directly affect sea level (floating ice displaces an equal volume of seawater), melting sea ice results in a positive feedback loop, where the loss of sea ice results in warmer surface seawater temperatures, which result in more melting, which results in less sea ice to reflect the sun’s energy back into the atmosphere, etc. This feedback loop has global climate and sea level implications, as the regional warming accelerates the melting of land based ice sheets and glaciers in Greenland, Antarctica and other high latitude land areas. Melting land based ice and snow contribute to sea level rise.
The Antarctic is much colder than the Arctic and observations have not revealed consistent trends in the seasonal extent of coastal sea ice. The continent of Antarctica is surrounded by coastal glaciers and ice shelves which appear to be relatively stable. The Larsen B and Wilkins ice shelves, however, have been disintegrating dramatically over the past few years.
IPCC 2007 observation: Arctic sea-ice extent has retreated by about 10 to 15% since the 1950s.