Arctic sea ice continues to lose
mass year after year and we appear to have less than in 2007 which established
the low point. What this means though is
rather significant.
1
The low in 2007 took a major and unique set of wind
conditions that concentrated the ice.
Nothing of the kind took place this year and the current situation
reflects substantially less ice than in 2007.
2
Multi year ice continues to erode and disappear. What ever is driving these losses have not
abated at all.
3
The US Navy claims that the ice has recovered since
2007. I continue to see no other evidence
whatsoever that that may be true.
4
The sea routes continue to shuffle open and closed, now
dependent on lucky weather conditions.
The arctic sea ice mass has
sharply contracted over the past decade in a continuation of a decadal
downtrend that had already removed over a third of the mass. The question we need to answer is whether or
not the process has largely ended or not.
As I stated above, the argument for ice recovery remains completely uncompelling. Yet we also sense signs that it may well be stabilizing. Otherwise we would be seeing a more
convincing collapse.
Arctic sea ice at record low for July
August 3, 2011
Arctic sea ice extent averaged for July 2011 reached the lowest level
for the month in the 1979 to 2011 satellite record, even though the pace of ice
loss slowed substantially during the last two weeks of July. Shipping routes in
the Arctic have less ice than usual for this time of year, and new data
indicate that more of the Arctic 's store of
its oldest ice disappeared.
Figure 1. Arctic sea ice extent for July 2011 was 7.92 million
square kilometers (3.06 million square miles). The magenta line shows the 1979
to 2000 median extent for that month. The black cross indicates the geographic
North Pole. Sea Ice Index
data. About
the data.
—Credit: National Snow and
Overview of conditions
Average ice extent for July 2011 was 7.92 million square kilometers (3.06 million square miles). This is 210,000 square kilometers (81,000 square miles) below the previous record low for the month, set in July 2007, and 2.18 million square kilometers (842,000 square miles) below the average for 1979 to 2000.
On July 31, 2011 Arctic sea ice extent was 6.79 million square
kilometers (2.62 million square miles). This was slightly higher than the
previous record low for the same day of the year, set in 2007. Sea ice coverage
remained below normal everywhere except the East Greenland
Sea .
Figure 2.
The graph above shows daily Arctic sea ice extent as of August 2, 2011,
along with daily ice extents for previous low-ice-extent years. Light blue
indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows
2008, and dark gray shows the 1979 to 2000 average. The gray area around the
average line shows the two standard
deviation range of the data. Sea Ice Index data.
—Credit: National Snow and
Conditions in context
During the first half of July, Arctic sea ice extent declined at a relatively fast pace (see July 18 post). But ice loss slowed substantially over the latter half of the month as the weather changed.
Through July, sea ice declined at an average pace of 90,200 square
kilometers (34,800 square miles) per day, which is slightly faster than the
average for 1979 to 2000 of 84,400 square kilometers (32,600 square miles) per
day. Ice loss slowed towards the end of July as a high-pressure cell centered
over the northern Beaufort Sea broke down and a series of low-pressure systems
moved over the central Arctic Ocean . This
change brought cooler conditions and likely pushed the ice apart into a thinner
but more extensive ice cover.
Figure 3.
Monthly July ice extent for 1979 to 2011 shows a decline of 6.8% per
decade.
—Credit: National Snow andIce
Data Center
—Credit: National Snow and
July 2011 compared to previous years
Average Arctic sea ice extent for July 2011 was the lowest for July in the satellite data record. The previous lowest year for July was 2007, which went to break the record for the lowest ice extent at the end of the melt season. Including 2011 the linear trend for July now stands at -6.8% per decade.
Figure 4. These maps show sea ice concentration (left) and ice age
(right) over the Arctic Ocean . In the Beaufort
Sea off the coast of Alaska
—Credit: NSIDC, data courtesy M. Tschudi
New ice age measurements show decline in oldest, thickest ice
Researchers look at ice age as a way to estimate ice thickness. Ice thickness matters to the overall stability of the ice cover, because older ice grows thicker over multiple seasons, while newly formed ice tends to be thin and vulnerable to melt. While the amount of older sea ice has increased somewhat since September 2007, an updated analysis of satellite-derived sea ice age recently published by James Maslanik and co-authors show the oldest ice (ice older than five years), has continued to decline.
Until recently, the central Arctic Ocean
and Canadian Archipelago served as refuges for some of the oldest, thickest
ice. However, the new data show that ice age is now declining in these areas. A
map of ice age for the third week of July, combined with sea ice concentration
for July 31, 2011 (Figure 4) shows that in the eastern Beaufort Sea, the ice has
essentially melted back to the edge of the multi-year ice cover (ice older than
one year). Multi-year ice is more resistant to melting completely in summer, so
it is not yet clear how much more ice will melt. Another tongue of old ice
extends from near the pole towards the New Siberian
Islands .
Between late March and late July first-year (younger) Arctic sea ice
has declined by 30%, multi-year ice has declined by 14%, and the oldest ice, or
ice older than 5 years, has declined by 16% . For background information on ice
thickness, see the new post on NSIDC's Icelights.
Figure 5.
This time series shows total sea ice area (top) and multi-year ice area
(bottom) for selected years within the Western Parry Channel route of the Northwest Passage . The black line with red dots shows
2011, other colors show ice conditions in different years.
—Credit: NSIDC courtesy Stephen Howell, Environment
Ice loss in Arctic shipping routes
Over the past few weeks, the sea ice edge has retreated from the shores of Siberia and Eurasia, potentially opening up much of the Northern Sea Route, the shipping lane that runs along the Eurasian Arctic coast from Murmansk on the Barents Sea, along Siberia, and through the Bering Strait. Higher resolution data such as the Multisensor Analyzed Sea Ice Extent (MASIE) indicate that some ice remains, particularly in the
On the other side of the Arctic, the Northwest
Passage is still choked with ice. However, data provided by
Stephen Howell of Environment Canada show that ice loss in the Northwest
Passage is well ahead of average (Figure 5), nearly matching last year when,
according to Canadian Ice Service (CIS)
analyses, sea ice in the Parry Channel (the northern part of the Northwest
Passage) reached the lowest levels in the CIS records dating back to 1968.
Whether a navigable channel does indeed open this year will depend on weather
conditions through the next few weeks, but so far, it looks possible.
Please note that NSIDC is not an operational ice forecasting center.
For shipping purposes, please consult the Canadian Ice Service or the US National Ice Center.
References
Further Reading
Tivy, A., S. E. L. Howell, B. Alt, S. McCourt, R. Chagnon, G. Crocker,
T. Carrieres, and J. J. Yackel. 2011. Trends and variability in summer sea ice
cover in the Canadian Arctic based on the Canadian Ice Service Digital Archive,
1960–2008 and 1968–2008, Journal of Geophysical Research, 116,
C03007, doi:10.1029/2009JC005855.
For previous analyses, please see the drop-down menu under Archives in
the right navigation at the top of this page.
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