Sea ice in the Arctic Circle.Arctic sea ice has seen a dramatic decline in recent decades.  Ine

Sea ice in the Arctic Circle.Arctic sea ice has seen a dramatic decline in recent decades.  Inevery geographic area, month and season, Arctic sea ice is lowertoday than in the 1980s and 1990s.As temperatures increase, the ice could become extremely vulnerableto natural variability in cycles (such as the Arctic Oscillation). Many global climate models predict that before the end of thiscentury, the Arctic will be ice-free for at least part of the year. Some suggest that the Arctic will be entirely ice-free bymid-century.Declining sea ice will lead to habitat loss for seals and polarbears.  Indigenous Arctic peoples have already reported changes inthe health and numbers of polar bears.As sea ice retreats from coastlines, wind-driven waves and permafrostthawing will lead to more rapid coastal erosion.Some scientists suggest that melting sea ice could interfere withocean circulation.  In the Arctic, the sinking of dense salty waterdrives ocean circulation.  Fresh meltwater (coming mostly from theGreenland Ice Sheet) could interfere with high-latitude oceancirculation, slowing it down.  Changes in the location and timing ofsea ice growth (where this dense salty water forms and sinks) couldalso be an important factor.Sea ice is also believed to stabilize ice shelves.  It is too thin tophysically buttress an ice shelf, but intact sea ice can preserve thecool conditions that stabilize it.  Air masses passing over sea iceare cooler than over open ocean (because the ice “insulates” thewater below, and prevents heat loss into the atmosphere).  Sea icecan also lessen the effect of ocean waves that would otherwise flexthe ice shelf and cause its breakup.The disintegration of ice shelves causes global sea levels to rise. And because most ice shelves are fed by glaciers, this will oftenlead to glacier acceleration, which also increases the sea level. Glacier acceleration has already been observed on the AntarcticPeninsula. -- source link

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