Imagery from the NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) shows that the southern route of the Northwest Passage as well as the Northern Passage are now free of sea ice.

2011 is the fourth consecutive year – and the fourth time in recorded history – that both Arctic shipping routes have become open to navigation.

Arctic ice extent is declining at a brisk pace, but melt is slightly behind the pace set in 2007, the record low year – as seen in this image at the IJIS Web site provided by the Japan Aerospace Exploration Agency (JAXA).

The National Snow and Ice Data Center (NSIDC) reports weather conditions in late July spread the ice out, but that conditions are now again such that sea ice extent may decline rapidly:

During early summer, a high-pressure cell persisted over the northern Beaufort Sea, promoting ice loss. This weather pattern broke down toward the end of July, slowing ice loss but spreading out the ice pack, making it thinner on average. The weather has now changed again, bringing another high-pressure pattern. Winds associated with this pressure pattern generally bring warm temperatures, and tend to push the ice together and reduce overall extent. In the Kara Sea, the combination of a high-pressure cell with low pressure to the west has resulted in strong northward ice movement, pushing the ice pack away from the coast and reducing ice extent. The same weather pattern is also increasing the movement of ice out of Fram Strait, between Greenland and Spitsbergen.

Right now, there is a record divergence between area and extent, as Neven reports at Arctic Sea Ice Blog. The difference is often substantial, as can be seen by comparing the graph of sea ice extent, above, with that of sea ice area, below, posted by Joseph Romm at Climate Progress.

The ratio of sea ice area to sea ice extent is now at a record low, as seen in the graph below.

NSIDC also reports that Arctic sea ice volume is now showing record lows. Through July 20 this year, the ice surface was melting faster than the underside of the ice. As the Arctic days grow shorter surface melt will slow – but ocean waters warmed during the summer will continue to melt the ice from below, reducing ice thickness and extent into September.

The University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) model projects that this year’s minimum volume in September will very likely finish below 2007, reaching a new record low volume.

The National Snow and Ice Data Center (NSIDC) reports average Arctic sea ice extent for July 2011 was the lowest level for the month since satellite records began in 1979.

Ice loss slowed substantially over the latter half of the month as the weather changed. 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, bringing cooler conditions and likely pushing the ice apart into a thinner but more extensive ice cover.

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.

In the first week of August, with a month or more to go in the melt season, Arctic sea ice area has already dropped below not just the year-to-date values, but the annual low points of any satellite-era year before 2007.

Shipping routes in the Arctic have less ice than usual for this time of year, and more of the Arctic’s oldest ice has disappeared.

Sea ice concentration (left) and ice age (right) over the Arctic Ocean. In the Beaufort Sea off the coast of Alaska, ice has melted back to the edge of a tongue of older, thicker ice. In the "Ice Age" image, red shows ice 5 years old and older, green shows 4-year-old ice, light blue shows 3-year old ice, dark blue shows second-year ice, and purple shows first-year ice.

Over the past few weeks, the sea ice edge has retreated from the shores of Siberia and Eurasia, 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. Some ice remains, particularly in the East Siberian Sea, but the reduced ice cover in the region has already made the route feasible this year. Taking advantage of the early retreat of sea ice in the Kara and Barents seas, the tanker Perseverance set sail on June 29, 2011 from Murmansk, Russia, aided by two icebreakers; and completed the passage on July 14. The company plans to send six to seven more ships through the Northern Sea Route this summer.

On the other side of the Arctic, the Northwest Passage is still choked with ice. However, ice loss in the Northwest Passage is well ahead of average, nearly matching last year when sea ice in the Parry Channel (the northern part of the Northwest Passage) reached the lowest levels in records dating back to 1968.

In an unusual mid-month update, the National Snow and Ice Data Center (NSIDC) reports Arctic sea ice is now disappearing faster than in 2007, the year that saw a record low for sea ice extent at the end of the melt season in September:

Arctic sea ice extent declined at a rapid pace through the first half of July, and is now tracking below the year 2007, which saw the record minimum September extent. The rapid decline in the past few weeks is related to persistent above-average temperatures and an early start to melt. Snow cover over Northern Eurasia was especially low in May and June, continuing the pattern seen in April.

To date in July, air temperatures over the North Pole (at the 925 millibar level, or roughly 1,000 meters or 3,000 feet above the surface) were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) higher than normal.

NSIDC explains why the early ice melt is significant:

When sea ice starts to melt in spring, small ponds known as melt ponds form on its surface. The small pools create a darker surface (a lower albedo) that fosters further melt. How early sea ice melt starts is one indicator of how much the ice will melt in a given year. New research by Don Perovich and colleagues shows that an early start to sea ice melt increases the total amount of sunlight absorbed through the melt season.

Arctic sea ice volume continues to plunge to record lows, too . . .

. . . as older, multi-year ice is replaced by younger, thinner ice more susceptible to melting in the summer.

The Arctic’s death spiral continues.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice extent for June 2011 was the second lowest in the satellite data record. Average ice extent fell below that for June 2007, which had the lowest minimum ice extent at the end of summer, but was greater than in June last year.

The Japan Aerospace Exploration Agency posts this colorful graph showing the last ten years of Arctic ice cover.

Weather over the next few weeks will determine whether the Arctic sea ice cover will again approach record lows. Regardless, the long-term trend is clear.

The University of Washington’s Polar Science Center reports Arctic sea ice volume  for June 2011 averaged 15,700 km³ – 37% lower than the mean over the 1979 -2010 period, 47% lower than in 1979, and 2.5 standard deviations below the trend.

Total Arctic sea ice volume from PIOMAS showing the volume of the mean annual cycle, the current year, and 2007 (the year of minimum sea ice extent in September). Shaded areas indicate one and two standard deviations from the mean.

While in the graph above 2007 is shown as the year of minimum sea ice volume in September, in a recently published reanalysis of their data the scientists conclude 2010 saw a new record low:

The 2010 September ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record.

Neven at Arctic Sea Ice Blog has posted this graph by Wipneus showing all the trends in the period 2002-2011:

Arctic ice continues in its death spiral.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice extent for May 2011 was the third lowest in the satellite data record since 1979, continuing its long-term decline.

The chart below shows the lowest year for May was 2004, followed by 2006. The long-term rate of decline for May now stands at -2.4% per decade.

During the month of May, sea ice declined at a near average rate, while air temperatures in the Arctic remained generally above average.

Although ice extent is low for this time of year, ice extent at the end of summer largely depends on Arctic weather over the next few months. Years with dramatic ice loss, such as 2007, have been associated with comparatively warm, calm, and clear conditions in summer that have encouraged ice melt. Summers with slow melt rates are opposite and tend to be stormier than average. The number of storms influences how warm, windy and cloudy the Arctic summer is.

The chart below compares this year to 2007, which saw dramatic, record-breaking ice loss in the Arctic.

NSIDC explains why

The last four summers have been dominated by an atmospheric pattern known as the Arctic dipole anomaly, which has been associated with low sea ice extent at the end of summer. This pattern features unusually high pressure over the Beaufort Sea and unusually low pressure over the Kara and Laptev Seas, which promote warm southerly winds along the Siberian coast, helping to melt ice and push it away from the coasts and out of the Arctic Basin through Fram Strait.

While the atmospheric pattern for May 2011 bears some resemblance to the Arctic dipole anomaly pattern, the centers of the pressure anomalies are in different locations this year, and it is not yet clear whether the pattern will persist through the summer and contribute to low ice extent.

Arctic sea ice volume continues to drop, too. In this chart published at the Polar Science Center, shaded areas represent one and two standard deviations of the anomaly from the trend.

Sea ice volume is an important climate indicator, as it depends on both ice thickness and extent and is therefore more directly tied to climate forcing than extent alone.

A new assessment of the impacts of climate change in the Arctic finds that the changes in the sea ice on the Arctic Ocean and in the mass of the Greenland Ice Sheet and Arctic ice caps and glaciers over the past ten years have been dramatic and  and represent an obvious departure from the long-term patterns. The study is titled Snow, Water, Ice and Permafrost in the Arctic.

The assessment finds that the past six years (2005–2010) have been the warmest period ever recorded in the Arctic. The higher surface air temperature are driving changes in the cryosphere. Two components of the Arctic cryosphere – snow and sea ice – are interacting with the climate system to accelerate warming in a feedback loop. Loss of ice and snow in the Arctic enhances climate warming by increasing absorption of the sun’s energy at the surface of the planet. Temperatures in the permafrost have risen by up to 2 °C and the southern limit of permafrost has moved northward in Russia and Canada- a trend which could result in dramatically increased emissions of carbon dioxide and methane. Melting ice could change large-scale ocean currents. Melting glaciers and ice sheets worldwide have become the biggest contributor to global sea level rise. Arctic glaciers, ice caps, and the Greenland Ice Sheet are contributing much more to global sea level rise than previously measured. High uncertainty surrounds estimates of future global sea level, with latest models predicting a rise of 0.9 to 1.6 m above the 1990 level by 2100. But, the assessment cautions, the combined outcome of these effects is not yet known. Interactions (‘feedbacks’) between elements of the cryosphere and climate system are particularly uncertain.

The assessment was done by the Arctic Monitoring and Assessment Programme (AMAP), an international organization headquartered in Norway. Member nations include the eight Arctic rim countries: Canada, Denmark/Greenland, Finland, Iceland, Norway, Russia, Sweden, and the United States. Other nations and organizations participate as well.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice extent declined through April more slowly than usual, as cool conditions helped retain ice in Baffin Bay, between Canada and Greenland. Still, April 2011 continued the overall downward trend of the past thirty years, ranking fifth lowest in the satellite record. The two lowest years for April were 2007 and 2006.

University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) model of sea ice volume shows continued very low ice mass in the Arctic compared to previous decades.

Joseph Romm at Climate Progress reports on a study showing the Greenland ice sheet has been losing mass over the last decade.

Greenland ice mass anomaly – deviation from the average ice mass over the 2002 to 2010 period.

The National Snow and Ice Data Center (NSIDC) reports sea ice reached its maximum extent on March 7 this year. Sea ice extent on this date tied for the lowest winter maximum extent in the satellite record. Arctic sea ice extent for the month of March 2011 was the second lowest in the satellite record.

The amount of older, thicker ice has increased slightly over last year. Older ice that has survived several summer melt seasons tends to be thicker, while newer ice is thinner and more vulnerable to melt in summer. The trend of spring ice cover becoming increasingly dominated by younger and generally thinner ice (because of strong summer melting reducing the amount of ice surviving into winter) remains striking.

There is still almost none of the oldest ice, older than four years old, that used to dominate much of the Arctic Ocean.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice appeared to reach its maximum extent for the year on March 7, marking the beginning of the melt season. This year’s maximum tied with 2006 for the lowest in the satellite record.

Since the start of the satellite record in 1979, the maximum Arctic sea ice extent has occurred as early as February 18 and as late as March 31, with an average date of March 6. Sea ice extent in February and March tends to be quite variable, because ice near the edge is thin and often quite dispersed. The thin ice is highly sensitive to weather, moving or melting quickly in response to changing winds and temperatures, and it often oscillates near the maximum extent for several days or weeks.

The graph above shows daily Arctic sea ice extent as of March 22, 2011, along with daily ice extents for 2006, which had the previous lowest maximum extent, and 2007, the year with the lowest minimum extent in September.

This winter, the Arctic has seen the lowest December, January, and February (tied with 2005) sea ice extent in the satellite record.

Even more importantly, Arctic ice volume is also continuing its long-term decline.

Shaded areas show one and two standard deviations from the trend.

Monthly average Arctic ice volume for September 2010 was 78% below the 1979 maximum and 70% below its mean for the 1979-2009 period.

Arctic ice continues in its downward death spiral.

The National Snow and Ice Data Center reports Arctic sea ice extent for February 2011 tied with February 2005 as the lowest recorded in the satellite record.

Sea ice extent was particularly low in the Labrador Sea and Gulf of St. Lawrence.

The February trend is now at -3.0 percent per decade.

This year has already seen the lowest January sea ice extent in the satellite record. The persistence of low sea ice likely contributes to the cold and severe weather events experienced this winter in the U.S. and Europe.

The National Snow and Ice Data Center (NSIDC) reports that Arctic sea ice extent for January 2011 was the lowest in the satellite record for that month.

Ice extent in January 2011 remained unusually low in Hudson Bay, Hudson Strait (between southern Baffin Island and Labrador), and Davis Strait (between Baffin Island and Greenland). Normally, these areas freeze over by late November, but this year Hudson Bay did not completely freeze over until mid-January. The Labrador Sea remains largely ice-free.

Air temperatures over much of the Arctic were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above normal in January. The warm temperatures in January came from two sources: unfrozen areas of the ocean continued to release heat to the atmosphere, and the wind patterns accompanying the negative phase of the Arctic oscillation brought warm air into the Arctic.

Warm conditions in the Arctic and cold conditions in northern Europe and the U.S. are linked to the strong negative mode of the Arctic oscillation. Cold air is denser than warmer air, so it sits closer to the surface. Around the North Pole, this dense cold air causes a circular wind pattern called the polar vortex which helps keep cold air trapped near the poles. When sea ice has not formed during autumn and winter, heat from the ocean escapes and warms the atmosphere. This may weaken the polar vortex and allow air to spill out of the Arctic and into mid-latitude regions in some years, bringing potentially cold winter weather to lower latitudes.

Some scientists speculate that more frequent episodes of a negative Arctic Oscillation, and the stormy winters that result, are linked to the loss of sea ice in the Arctic. Jeff Masters at Wunder Blog explains:

It is possible that Arctic sea ice loss is largely responsible for the unusual Arctic Oscillation pattern we’ve observed during the past two winters, as well as for the record-strength ridges of high pressure observed over Greenland and Alaska this winter. It should not surprise us that Arctic sea ice loss would be capable of causing major perturbations to Earth’s weather, since it is well known that changes from average in sea surface temperatures over large regions of the ocean modify the jet stream, storm tracks, and precipitation patterns. The El Niño and La Niña patterns are prime examples of this (though the area of oceans affected by these phenomena are much larger than what we’re talking about in the Arctic.) Another example: Feudale and Shukla (2010) found that during the summer of 2003, exceptionally high sea surface temperatures of 4°C (7°F) above average over the Mediterranean Sea, combined with unusually warm SSTs in the northern portion of the North Atlantic Ocean near the Arctic, combined to shift the jet stream to the north over Western Europe and create the heat wave of 2003, the deadliest heat wave in history with 30,000 – 50,000 deaths in Europe.

Masters reports that near the end of January the negative Arctic oscillation pattern broke down and turned positive, which usually favors ice growth. The consequent spin-up of the polar vortex will tend to keep cold air bottled up in the Arctic, leading to more Arctic sea ice formation and warmer winter conditions over the U.S.