Recent projections on the extent of Arctic sea ice melt showed, though this year's melting would be significant, no new record would be set. New data for July from the National Snow and Ice Data Center confirms this trend, but importantly also reveals how older, thicker multi-year ice continues dramatic declines.
From the NSIDC:
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...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.
Thinner Ice More Vulnerable to Further Declines
Last year, Ron Kwok of NASA's Jet Propulsion Laboratory explained the significance of multi-year sea ice melting and the decreasing volume of sea ice: "Ice volume allows us to calculate annual ice production and gives us an inventory of the freshwater and total ice mass stored in Arctic sea ice. Even in years when the overall extent of sea ice remains stable or grows slightly, the thickness and volume of ice cover is continuing to decline, making the ice more vulnerable to continued shrinkage."
Arctic Practically Seasonally Ice-Free Today
In practical terms regarding new shipping routes opening up through the Arctic, according to David Barber from the University of Manitoba, it's really the multi-year ice that's the issue.
In October of last year, Barber argued, "from a practical perspective, we almost have a seasonally ice-free Arctic now, because multi-year sea ice is the barrier the use and development of the Arctic."
July's Ice Extent Second Lowest on Record
NSIDC reports average ice extent for July 2010 as 8.39 million square kilometers--the second lowest on record, 1.71 million square kilometers below the 1979 to 2000 mean, but 260,000 kilometers more than the average for the record setting low of July 2007. The average daily rate of decline for the month was 77,000 square kilometers; from 1979-2000 the average was 84,400 square kilometers.
Slowing the rate of ice decline were stormy, cloudy and relatively cool weather throughout the month.
More on Arctic Sea Ice:
Scientists Predict Continued Rapid Summer Arctic Sea Ice Decline - But No New Record
Arctic Sea Ice Loss Confirmed As Main Cause of Faster Polar Warming
Melting Arctic Sea Ice Won't Expand Carbon Storage Potential
Arctic Sea Ice Not Only Covers Less Area, It's Thinner Too