In an earlier post
, I wondered how scientists at CU in Boulder could be saying that usually the sea ice in the Northern Ocean was nearly 60% multi year old ice when all but 30% of it melts each Summer. As I suspected, the problem was in the area included in the study. Most scientists concentrate on all
the sea ice in northern seas. The CU guys concentrated on what the others call the Arctic Basin, the sea generally inside 80 degrees north latitude (actually more than the AB, but well less than the entire Northern Ocean). Much of that sea ice inside 80 degrees does
survive the Summer and therefore there should be lots of multi year ice.
, from the University of Illinois, is a record of what happened in just the AB over the last 366 days. A lot of it melted, a little more than a million square kilometers more than normal*. So to say that a lot more of the now completely recovered AB sea ice is new ice, less than a year old, is merely to repeat that a lot of it melted this past Summer. Not exactly 'news.'
But the guys at CU go a lot further and say that almost all of the 6 year old and older sea ice is gone
. They use a new microwave satellite device to detect, I believe, thickness and thus assign an age to the ice. I have no reason to doubt the instruments. I have no real way to dispute their findings. The trouble with this is that we have daily records, satellite photos, of the extent of the AB sea ice for the past 28 years. We can see if, in mid August (to late September) of the past 6 years, nearly all the old ice had melted. It really hasn't, although a lot does melt and in different areas even in the generally reliably ice covered area north of the Canadian Archipelago and Greenland. But different areas melting away throughout the AB are visible in the record in the early 80s as well. Whether the reduction from 20% to 6%, as the CU guys calculate, is wholly different from what happened in the 1930s or in, say, the Medieval Warm period, well before there was any appreciable anthropogenic atmospheric CO2, is necessarily speculation. I do know that some of the Icelandic writers between 1000 and 1150 AD noted a steep decline in the amount of sea ice around Greenland during their lifetimes. Is that information helpful? Hard to say. I guess I could call, even visit the CU guys, and try to get an answer. More later.
One last thought-- I'm troubled by the discussion of 'icebergs' in the story linked to above. Icebergs are really thick pieces of glaciers that generate on land and break off into the sea from time to time. They are distinct from the sea ice the generates in the ocean. What they have to do with sea ice is any one's guess. Could be the reporter is not fully up to snuff or the connection he wrote about was later edited out.
*The normal from satellite data since 1979.
Labels: Arctic Sea Ice; Melting of 'Old' Ice