Dr. Jeff Masters at WunderBlog reports that both the Northwest Passage and the Northern Sea Route are now open. Data at the University of Illinois site Cryosphere Today shows it is now possible to completely circumnavigate the Arctic Ocean in ice-free waters – and this will probably continue to be the case for at least a month.

Arctic sea ice extent image for August 24, 2010, as compiled by The University of Illinois Cryosphere Today. The northern route (Western Parry Channel) through the Northwest Passage was completely clear of ice, as was the Northeast Passage. The southern route through the Northwest Passage was still partially blocked.

This year marks the third consecutive year–and the third time in recorded history–that both the Northwest Passage and Northern Sea Route have melted free, according to the National Snow and Ice Data Center.

The Northeast Passage opened for the first time in recorded history in 2005, and the Northwest Passage in 2007. It now appears that the opening of one or both of these northern passages is the new norm.

Here’s an updated graphic:

As this graphic from Chris Mooney’s article in New Scientist shows, ice volume has been decreasing even more precipitously than ice area.

The average volume of Arctic ice between July and September has fallen from 21,000 cubic kilometres in 1979 to 8000 cubic kilometres in 2009, a 55% decline compared with the 1979 to 2000 average. This is even faster than the decline in ice extent, which is 40% below the long-term average.

Not only has the total volume of Arctic ice continued to decline since 2007 considerably more quickly than predicted by most climate models, the rate of loss is accelerating. The Arctic Ocean may soon be essentially ice-free during the summer months. The dark ocean waters, mostly devoid of ice, would then absorb still more sunlight, further warming the overlying atmosphere during an increasingly lengthy ice-free season, reshaping weather throughout the region and well beyond it.

A good friend recently asked me why I give so much attention to news about Arctic sea ice extent at this blog, saying he just glosses over posts on this subject.

Here’s the reason: the area of sea ice cover is an important, amplifying climate feedback. Loss of sea ice is a cause of concern because as the area of ice decreases, increased absorption of sunlight by the darker ocean causes more sea ice melting. As this graph from Makiko Sato & James Hansen’s new blog shows, Arctic sea ice extent has been declining steadily . . .

. . . as has sea ice volume. What ice remains is getting thinner.

It’s not just sea ice that is melting. Ice sheets are shrinking too, both in Greenland and in Antarctica.

And the ice loss over the last few years has been at a time of minimum solar irradiance. Solar irradiance is now once again on the upswing.

It seems likely that September Arctic sea ice may be all but gone within a few decades – or perhaps even sooner. What does less Arctic sea ice mean for Earth’s weather patterns?

NASA is predicting loss of summer sea ice will mean more severe winter storms in the northern hemisphere – a prediction which is already being borne out.

Following Arctic sea ice extent is fascinating because it shows that global warming is not something to worry about in the future. Global warming is here and now, and is already affecting us in our daily lives. What’s worrisome is that the impacts will only get more severe. By the time the impacts are bad enough to get our attention, it will be too late – the damage will already have been done. Under the best-case scenario it will take Earth a thousand years or more to recover. Under the worst-case scenario, Earth will flip into a different, stable climate regime which won’t be hospitable to human existence.

A number of stories appeared in the media last week about one of Greenland’s largest of  “outlet” glaciers (glaciers ending in the sea) calving an enormous ”ice island” of more than 100 square miles in size.

None of the stories had a good graphic showing what happened. Fortunately, WWF Climate Blog has posted this one:

The glacier has lost about a quarter of its floating ice shelf.

A 2009 survey of 34 of the widest Greenland marine-terminating glacier outlets from the inland ice sheet found the loss rate has been nearly constant since 2000.

Above: cumulative annual area changes for 34 of the widest Greenland ice sheet marine-terminating outlets. Source: Byrd Polar Research Center.

To put the Petermann Glacier’s latest ice island in perspective, the island’s area of at least 260 km² is well over twice what all 34 glaciers surveyed by the  Byrd Polar Research Center have been losing annually (-106 km² per year).

Scientists recently documented the breakup up of a 7 km² (2.7 square mile) section of another glacier in the region, the Jakobshavn Isbrae glacier. The calving front – where the ice sheet meets the ocean is now further inland than at any time previously observed.

Location of the successive calving fronts of the Jakobshavn Isbrae glacier between 1851 and 2009, overlain on a Landsat image from 7/29/2009. Source: NASA/Goddard Space Flight Center Scientific Visualization Studio. Historic calving front locations courtesy of Anker Weidick and Ole Bennike, Geological Survey of Denmark and Greenland.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice extent averaged for July 2010 was the second lowest in the satellite record, after 2007.

Stormy, cloudy, and relatively cool weather in July slowed the rate of ice loss. Now the old, thick ice that moved into the southern Beaufort Sea last winter is beginning to melt out.

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 points out it would take “a very unusual set of conditions” in August to create a new record low – the decline rate in August would have to match the record decline rate of August 2008.

The Polar Science Center reports that Arctic ice thickness is continuing its precipitate decline. September ice volume reached a record low in 2009, 67% below its 1979 maximum (for the 1979-2009 period). If the 2010 anomaly stays below the 2009 level -which looks like a pretty safe bet at this point – 2010 will see a new record low for ice volume.

A British research team studying the Greenland ice sheet has discovered evidence of a rapidly accelerating rate of melt: the ice sheet in the region they are studying has dropped six meters in just one month.

The shrinking of the glaciers is caused by surface melt, a vicious cycle in which melted ice brings about further thawing of the cap beneath it. Frozen ice has an “albedo”, or reflectivity, of around 80%, whereas open water reflects only around 20% of the sun’s rays. So as the ice melts and turns into water, its surface reflectivity decreases. It then absorbs even more of the heat from the sun, further accelerating the melting.

Black soot particles are also contributing, as shown in this photo in an article at Sky News.

Dr Hubbard shows how soot has pock-marked the ice

Dr. Alan Hubbard explains:

What you see in there is a bunch of particles of aeolian dust . . . and black soot and just particles that are in the air caused by industry or combustion engines. Because they are dark in color, compared to the ice that surrounds it, which is white, they absorb more of the sunlight and a lot more of its energy, which creates a positive feedback and so they effectively drill down into the surface of the ice sheet.

The National Snow and Ice Data Center (NSIDC) reports the rate of ice loss in the Arctic slowed in the first half of July, primarily because of a change in atmospheric circulation as the dipole anomaly, an atmospheric pattern that dominated the Arctic in June, broke down.

The report explains:

Through much of May and June, high pressure dominated the Beaufort Sea with low pressure over Siberia. Winds associated with this pattern, known as the dipole anomaly, helped speed up ice loss by pushing ice away from the coast and promoting melt.

However, the dipole anomaly pattern broke down in early July. In the first half of July, cyclones (low pressure systems) generated over northern Eurasia tracked eastward along the Siberian coast and then into the central Arctic Ocean, where they tend to stall. This cyclone pattern is quite common in summer. The low-pressure cells have brought cooler and cloudier conditions over the Arctic Ocean. They have also promoted a cyclonic (anticlockwise) sea ice motion, which acts to spread the existing ice over a larger area. All of these factors likely contributed to the slower rate of ice loss over the past few weeks.

In the last few days, high pressure has started to build again in the Beaufort Sea, but whether this will continue remains to be seen.

Still, Arctic sea ice extent at this time is the second lowest ever recorded, as seen in this chart from the Japan Aerospace Exploration Agency website, IJIS.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice declined at the fastest rate ever recorded in June, and the average ice extent in June was the lowest in the satellite data record (from 1979 to 2010).

The previous record for the fastest rate of June decline was set in 1999. The linear rate of monthly decline for June over the 1979 to 2010 period is now 3.5% per decade.

Whether or not 2010 will see a new record low set for Arctic sea ice extent depends upon weather patterns. NSIDC explains:

The record low ice extent of September 2007 was influenced by a persistent atmospheric pressure pattern called the summer Arctic dipole anomaly (DA). The DA features unusually high pressure centered over the northern Beaufort Sea and unusually low pressure centered over the Kara Sea, along the Eurasian coast. In accord with Buys Ballot’s Law, this pattern causes winds to blow from the south along the Siberian coast, helping to push ice away from the coast and favoring strong melt. The DA pattern also promotes northerly winds in the Fram Strait region, helping to flush ice out of the Arctic Ocean into the North Atlantic. The DA pattern may also favor the import of warm ocean waters from the North Pacific that hastens ice melt.

June 2010 saw the return of the DA, but with the pressure centers shifted slightly compared to summer 2007. As a result, winds along the Siberian coastal sector are blowing more from the east rather than from the south. Whether or not the DA pattern persists through the rest of summer will bear strongly on whether a new record low in ice extent is set in September 2010.

In Antarctica, a robot submarine sent beneath the Pine Island glacier’s floating ice sheet has shown that the glacier has become unpinned from an undersea ridge and that warm water is now circulating under the ice, causing the glacier to melt even faster in an accelerating feedback loop.

The study, Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat, is published in Nature Geoscience.

The 400 meter- high ridge has previously been anchoring the glacier and preventing warm seawater from reaching the ice, melting it from underneath.  A modeling study published in January suggested that once the glacier retreated behind the ridge, the glacier would not be able to recover.

Pine Island glacier is one of a handful in West Antarctica which together are estimated to be responsible for about 10% of global sea-level rise.

At the other end of the world, scientists are predicting that September 2010 will see yet another “critical minimum” for Arctic sea ice.

One forecast, contained in the September Sea Ice Outlook: June Report, was developed by the team from Klima Campus of the University of Hamburg. It estimates a September minimum of 4.7 million square kilometers. Another estimate produced by AWI researchers is a bit higher – 5.2 million km². Neither of the two research groups anticipates that the record minimum of 4.3 million km² in 2007 will be reached. But scientists caution that the decisive factors for the situation in late summer, such as the ice thickness in the central Arctic and further development of the weather in summer, are not yet known.

What is known is that Arctic sea ice volume is falling off a cliff.

Continuously updated Arctic Sea Ice Volume Anomaly from PIOMAS. 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. Click on image for a larger version of the figure

It’s approaching the end of June, and Arctic sea ice is continuing to melt precipitously.  Arctic sea ice is shrinking at a record pace both in extent . . .

. . . and in volume:

We’ve never seen anything like current conditions in the historical record.

The National Snow and Ice Data Center (NSIDC) reports that by the end of May, Arctic ice extent had fallen to near the 2006 level, the lowest in the satellite record for the end of that month.

NSIDC explains why Arctic ice went so rapidly from near normal to approach record lows:

[S]everal regions of the Arctic experienced a late-season spurt in ice growth. As a result, ice extent reached its seasonal maximum much later than average, and in turn the melt season began almost a month later than average. As ice began to decline in April, the rate was close to the average for that time of year. In sharp contrast, ice extent declined rapidly during the month of May. Much of the ice loss occurred in the Bering Sea and the Sea of Okhotsk, indicating that the ice in these areas was thin and susceptible to melt. Many polynyas, areas of open water in the ice pack, opened up in the regions north of Alaska, in the Canadian Arctic Islands, and in the Kara and Barents and Laptev seas.

The polynyas are clearly visible in high-resolution passive microwave images from the Advanced Microwave Sounding Radiometer (AMSR-E) aboard NASA’s Aqua satellite. What do current ice conditions mean for the minimum ice extent this fall? It is still too soon to say: although ice extent at present is relatively low, the amount of ice that survives the summer melt season will be largely determined by the wind and weather conditions over the next few months.

Analysis from scientists at the University of Washington shows that ice volume has continued to decline precipitously.

Joseph Romm comments at Climate Progress on a presentation by Wieslaw Maslowski of the Naval Postgraduate School, one of the country’s leading experts on the Arctic, indicating the Arctic is in a death spiral.  By 2016 (+/- 3 yrs) the Arctic will be essentially ice-free by the end of the melt season – decades ahead of the projections in the 2007 IPCC report.

And here’s the latest multi-year chart of Arctic ice extent from the Japan Aerospace Exploration Agency website.