"Second lowest July Arctic sea ice extent. Thickest ice begins melt out, so we may see record low volume"
Will we see Arctic sea ice records broken this September for both volume and extent?
The National Snow and Ice Data Center just issued their full July report, which suggests that, because of “cool, stormy weather” last month, “It would take a very unusual set of conditions in August to create a new record low.”
The Study of Environmental Change’s September Sea Ice Outlook: July Report, which surveys forecasters, says “The spread of Outlook contributions suggests about a 29% chance of reaching a new September sea ice minimum in 2010.”
You can see what appears to be a change in slope in the last few days, but the Arctic weather is fickle, so the extent of the extent in September remains unclear.
As for volume, the NSIDC report spotlights the demise of some of the oldest and thickest ice left:
Arctic sea ice extent averaged for July was the second lowest in the satellite record, after 2007. After a slowdown in the rate of ice loss, the old, thick ice that moved into the southern Beaufort Sea last winter is beginning to melt out….
Older, thicker ice melting in the southern Beaufort Sea This past winter’s negative phase of the Arctic Oscillation transported old ice (four, five, and more years old) from an area north of the Canadian Archipelago. The ice was flushed southwards and westward into the Beaufort and Chukchi seas, as noted in our April post. Ice age data show that back in the 1970s and 1980s, old ice drifting into the Beaufort Sea would generally survive the summer melt season. However, the old, thick ice that moved into this region is now beginning to melt out, which could further deplete the Arctic’s remaining store of old, thick ice. The loss of thick ice has been implicated as a major cause of the very low September sea ice minima observed in recent years.
For background, see Study: “It is clear “¦ that the precipitous decline in September sea ice extent in recent years is mainly due to the cumulative loss of multiyear ice.” The Southern Beaufort Sea is famously full of rotten ice.
This map of ice age for the end of July, 2010, shows a region of open water north of Alaska, where old, thick ice has melted out.
NSIDC has yet more interesting data on the death of old, thick ice:
High-resolution images from MODISHigh-resolution (250-meter) visible imagery from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor vividly shows the loss of the old, thick ice. A chunk of old ice has broken away from the main pack and come to rest along the north coast of Alaska, east of Point Barrow, where it has begun to melt in the warm shallow shelf waters. While cloud cover obscures some areas, it is clear that the old ice floe has broken up into many smaller floes. Whether this old ice will completely melt out by the end of summer will depend to some extent on weather conditions. However, smaller floes melt more easily than consolidated ice. This behavior is becoming more typical of the ice pack as the ice thins.
This image from NASA’s MODIS sensor on the Aqua satellite on July 25, 2010 shows an individual floe of old ice, which broke away from the main ice pack and is melting away.
And while everyone’s eyes are on the Arctic sea ice extent data, the Polar Science Center’s PIOMAS model updated for July 31 still puts the far more important metric of Arctic ice volume at a record-smashing low, with a little pullback on the anomaly:
Daily Sea Ice volume anomalies for each day are computed relative to the 1979 to 2009 average for that day. The trend for the 1979- present period is shown in blue. Shaded areas show one and two standard deviations from the trend.
Note that PSC says, “September Ice Volume was lowest in 2009 at 5,800 km^3 or 67% below its 1979 maximum.” I have been informed by PSC that the “daily averaged chart” is not in fact a chart of the average thickness for that day over the 1979 to 2009 period, so it is a bit hard to tell exactly what the absolute thicknesses. Obviously, we will set a record if the 2010 anomaly stays below the 2009 level, which at this point still seems to be a good bet.