Why Arctic sea ice is shrinking

[phantom power]

There's more discussion thru the link. This part about Arctic Oscillation fascinated me:

The Arctic Oscillation is an observed natural pattern of surface pressure variations in the Northern Hemisphere. The "positive index" of the AO is defined when the surface pressure is below normal at the north pole and above normal at about 45 degrees north latitude. Positive Arctic Oscillation conditions steer storms farther north, bringing stronger surface westerly winds in the North Atlantic and warmer and wetter than normal conditions to the Arctic and northern Europe. The winds and ocean currents during the positive Arctic Oscillation mode tend to drive sea ice from west to east along the north shore of Canada, then out of the Arctic Ocean through the channel of water to the east of Greenland (Fram Strait).



When one looks at the wintertime pattern of the Arctic Oscillation (AO) over the past 100 years, a mostly random pattern of positive and negative AO modes is apparent (Figure 1). However, one anomalous period is very striking: a string of seven consecutive years with a positive AO, including two years (1989 and 1990) with the highest AO index ever observed. During this period, strong westerly winds rapidly flushed more than 80% of the oldest, thickest sea ice out of the Arctic Ocean, leaving most of the Arctic covered with ice less than three years old (Figure 2). Younger ice is much thinner, and melts much more readily. Rigor and Wallace (2004) estimate that at least half of the loss of sea ice in the Arctic since 1979 is due to these six years of strange weather with very low surface pressure over the Arctic. Did climate change cause this unusual pattern between 1989 and 1995? It is possible, but no one has published any papers showing how this might have occurred. For now, the assumption is that this major loss of Arctic sea ice due to wind patterns between 1989-1995 is natural.

The big concern is that since the strange positive Arctic Oscillation years of 1989-1995, a number of years with negative AO have occurred. Normally, during negative AO years, ice extent and thickness increase in the Arctic. But instead, ice extent and thickness during 2002-2006 have shown an unprecedented series of record minima, giving rise to fears that we are on our way to an ice-free Arctic later this century.



Figure 2. The change in age and thickness of sea ice between 1987 and 2005. In 1987, most of the Arctic sea ice was old and thick, generally more than ten years old. A period of strong positive Arctic Oscillation conditions between 1989 and 1995 created winds and currents that flushed most of this old ice out of the Arctic Ocean, through Fram Strait to the east of Greenland. The new ice that replaced the old ice is much thinner. Image credit: Rigor, I. G., and J. M. Wallace (2004), "Variations in the age of Arctic sea-ice and summer sea-ice extent," Geophys. Res. Lett., 31, L09401, doi:10.1029/2004GL019492.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=625&tstamp=200702

[kestrel91316]

1. For us laypersons: arctic sea ice is shrinking because the earth's

atmosphere is filling up with CO2 and the planet is OVERHEATING.

[phantom power]

2. More than that. Since this ice is thinner, the coverage will be decreasing faster...

It will break up easier. It will expose more low-albedo sea water to the sun's heat energy. And another implication: If we experience another round of extra intense positive AO, it also means that some huge portion of it might just blow away one year. Sort of begs the question: do the current warming conditions make positive AO more or less likely?

[phantom power]

3. Self-kick for "80% arctic sea ice 'flushed' in one 5-year period"

[Porcupine]

4. Kick, very important, read twice. nt.

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