Arctic sea ice below 2005 record single-day absolute minimum record

On 17 August 2007 [Yesterday and today], Arctic sea ice surpassed the
previous single-day (absolute minimum) record for the lowest extent
ever measured by satellite. Sea ice extent has fallen below the 2005
record low absolute minimum and is still melting. Sea ice extent is
currently tracking at 5.26 million square kilometers (2.02 million
square miles), just below the 2005 record absolute minimum of 5.32
million square kilometers (2.05 million square miles).


Arctic Sea Ice News Fall 2007

During the crucial summer melting season, scientists monitor the
condition of Arctic sea ice for comparison to previous years. For more
on the importance of sea ice and how scientists monitor it, please see
our Frequently Asked Questions.

Please see Press Information for details of interest to journalists.
Ongoing commentary and updates from NSIDC

From August 10, 2007 through the end of the summer melt season, we
will post updates as events warrant, below. To view previous updates,
scroll down. For automatic updates, see our RSS Feed.


Overview of current sea ice conditions
Sea ice extent continues to decline; it is currently tracking at 4.92
million square kilometers (1.89 million square miles), below the 2005
record absolute minimum of 5.32 million square kilometers (2.05
million square miles).

[[Images at the cite]]


Figure 1: Sea ice extent for August 21, 2007

Graphic showing sea ice in Arctic

Please note that our daily sea ice images, derived from microwave
measurements, may
show spurious pixels in areas where sea ice may not be present. These
artifacts are
generally caused by coastline effects, or less commonly by severe
weather. Scientists
use masks to minimize the number of "noise" pixels, based on long-term
extent patterns.
Noise is largely eliminated in the process of generating monthly
averages, our standard
measurement for analyzing interannual trends. Data derived from Sea
Ice Index data set.
Credit: National Snow and Ice Data Center.

See High Resolution Image


Current sea ice conditions: August 21, 2007

Figure 1 provides a map of sea ice extent for August 21, 2007. Sea ice
extent now stands at 4.92 million square kilometers (1.89 million
square miles). The magenta line shows the median August sea ice extent
based on data from 1979 to 2000.



Figure 2: Summer melt season Arctic sea ice extent

Plot of this year's sea ice against other years

Data derived from Sea Ice Index data set. Credit: National Snow and
Ice Data Center.
See High Resolution Image


Current sea ice conditions in context

Figure 2 is the updated time series of daily sea ice extent for 2007,
2005, and the 1979 to 2000 average. As mentioned above, sea ice extent
on August 21 was 4.92 million square kilometers (1.89 million square
miles). Compared to conditions cited in our August 17 update, we have
lost an additional 340,000 square kilometers (131,000 square miles) of
ice, an area larger than the the state of New Mexico. Ice extent is
now well below the previous lowest absolute minimum extent of 5.32
million square kilometers (2.05 million square miles) recorded on
September 20-21 of 2005, and there is likely several weeks of further
melt ahead of us.

Figure 3: Arctic sea ice image from August 11, 2007

Satellite image of Arctic above Greenland

Data: from MODIS satellite. Credit: National Snow and Ice Data Center.
High Resolution Image


The opening of the Northwest Passage

Of particular note is imminent opening of the fabled Northwest Passage
through the channels of the Canadian Arctic Archipelago. This shortcut
between the Atlantic and Pacific oceans was first navigated by Roald
Amundsen in the early 1900s. It took his group over two years of
arduous and dangerous navigation through narrow lanes of open water
amongst thick, compact ice. Analysts at the Canadian Ice Service and
the U.S. National Ice Center confirm that the passage is almost
completely clear and that the region is more open than it has ever
been since the advent of routine monitoring in 1972. The Northwest
Passage traces from Baffin Bay in the South toward M'Clure Strait.

A high-resolution look at sea ice

Figure 3 is based on high-resolution satellite data. We have zoomed in
on an area of sea ice to show some of the unusual conditions that this
year has brought. Note the immense chunks of sea ice (ice floes), some
of them with melt ponds, visible as blue flecks on the ice. Normally,
this region is a consolidated ice pack rather than individual floes.
The ice edge has pulled back much further than normal from the coast.

Figure 4: Disappearance of old ice, 1982-2007

Movie showing old sea ice gradually disappearing in later years

Credit: Animation from NSIDC courtesy of C. Fowler and J. Maslanik;
Colorado Center
for Astrodynamics Research.
(High Resolution Image Not Available)


Changes in ice age and thickness

Another aspect of the story for 2007 is the "memory" of the sea ice to
changes over the past few decades. Specifically, there seems to have
been a transition to younger, thinner ice beginning in the late 1970s.
This reflects not only trends towards more summer melt and less winter
ice growth, but changing winds that have transported fairly thick ice
out of the Arctic Ocean into the North Atlantic, and decreased the
length of time that ice is "sequestered" in the Arctic Ocean where it
might have a chance to grow thicker.

Ice that has survived through one summer, called second-year ice, is
typically thicker than first-year ice, and ice that has survived
several summers is assumed to be thicker than second-year ice. To
estimate ice age, our colleagues Chuck Fowler and Jim Maslanik at the
University of Colorado used drifting buoy data along with information
from satellites to assess the formation, transport, and melt of the
ice, which they in turn used to estimate ice age. Results from this
study reveal the area of oldest ice (i.e., ice older than four years)
is decreasing in the Arctic Ocean, and being replaced by younger, and
therefore, thinner ice. The region of the oldest (and thus thickest)
ice is now confined to a relatively small area north of the Canadian
Archipelago. Replenishment of old, thick ice is essential to the
maintenance and stability of the Arctic summer ice cover, since
thinner ice requires less energy to completely melt out in summer than
thicker ice.

Figure 4 shows an animation of ice age in the Arctic from 1981 through
2007. The colors indicate the age of the sea ice in years; light blue
is open water (OW). Areas in red are locations where the ice is five
years or older, whereas the dark blue areas are first-year ice. The
overall reduction in ice age over the past twenty-six years becomes
evident as the animation runs through the years. The animation also
shows seasonal variations in the ice cover as the first-year ice melts
in the summer and regrows in the winter.



Figure 5: Cloud cover in June and July of 2007

Graphic showing Arctic cloud cover

Data derived from MODIS. Credit: Image from NSIDC courtesy W. Chapman,
University of Chicago, Urbana Champaign.
See High Resolution Image


A note on cloud-cover over June and July of 2007

Our August 14 entry commented on the role of unusually clear skies and
high temperatures in fostering rapid melt.

Our colleague William Chapman of the University of Illinois, Urbana
Champaign, has examined cloud conditions more closely. Figure 5 is his
plot of percent anomalies in Arctic cover for June through July, 2007,
calculated in comparison to mean conditions over the period 2000 to
2006. Areas in green and blue are where cloud cover was less than
normal. Note the large reductions in cloud cover north of Alaska
compared to 2000 to 2006, consistent with rapid sea ice melt as more
solar energy than usual reached the ice surface.

Ongoing high pressure, high temperatures, and clear skies

Atmospheric data averaged for August 1-18, 2007, show high atmospheric
pressure still prevailing over the Arctic Ocean north of Alaska, with
low atmospheric pressure in the Laptev Sea, broadly similar to the
pattern seen for June through July. The high-pressure cell points to
an ongoing tendency for relatively clear skies north of Alaska (as
seen in Figure 3 above). Temperatures at 925 millibars (about 2,500
feet) have continued to be above normal across most of the Arctic
Ocean, especially north of eastern Siberia, where winds are bringing
in warm air from the south. This wind pattern has also continued to
push ice away from the Siberian coast and into the central Arctic
Ocean.
17 August 2007 [top]

Overview of current sea ice conditions
Yesterday and today, Arctic sea ice surpassed the previous single-day
(absolute minimum) record for the lowest extent ever measured by
satellite. Sea ice extent has fallen below the 2005 record low
absolute minimum and is still melting. Sea ice extent is currently
tracking at 5.26 million square kilometers (2.02 million square
miles), just below the 2005 record absolute minimum of 5.32 million
square kilometers (2.05 million square miles).


http://nsidc.org/news/press/2007_seaiceminimum/20070810_index.html

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