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 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.

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

]]> http://casafoodshed.org/archives/2010/06/28/ice-is-melting-at-the-ends-of-the-world/feed/ 0 http://casafoodshed.org/archives/2010/06/23/arctic-sea-ice-melting-at-record-pace/ http://casafoodshed.org/archives/2010/06/23/arctic-sea-ice-melting-at-record-pace/#comments Wed, 23 Jun 2010 18:12:41 +0000 jim http://casafoodshed.org/?p=5447 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.

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.

The Japan Aerospace Exploration Agency (JAXA) has a terrific graphic on its website showing multiple years of Arctic ice extent. As you can see, it’s much too early to predict that 2010 will see a new record low, although conditions in the Arctic such as areas of open water in the pack ice and broad areas of more scattered ice cover indicate that the ice may be posed to retreat rapidly.

The area of sea-ice cover is often defined in two ways: sea-ice “extent” and sea-ice “area.” Sea ice extent is defined as the areal sum of sea ice covering the ocean (sea ice + open ocean), whereas the “area” definition counts only sea ice covering a fraction of the ocean (sea ice only). Thus, the sea-ice extent is always larger than the sea-ice area.

Regardless of ice extent, Arctic ice volume continues to hit record lows.

During April, Arctic sea ice extent declined at a steady pace, remaining just below the 1979 to 2000 average. Ice extent for April 2010 was the largest for that month in the past decade. At the same time, changing wind patterns have caused older, thicker ice to move south along Greenland’s east coast, where it will likely melt during the summer. Temperatures in the Arctic remained above average.

The very late maximum ice extent, on March 31, means that the melt season started almost a month later than normal. This graph shows that ice extent has now begun to plunge.

The Polar Science Center at the University of Washington reports total Arctic ice volume for March 2010 was the lowest over the 1979-2009 period and 38% below the 1979 maximum.

While itself a consequence of climate change, the shrinking Arctic ice cap is contributing to a positive feedback loop in which global warming and loss of ice reinforce each other. White sea ice reflects most of the incoming sunlight back into space. But when the ice melts, more heat is absorbed by the darker water, which in turn heats the atmosphere above it.

An APF story about the study quotes study co-author James Screen:

It was previously thought that loss of sea ice could cause further warming. Now we have confirmation this is already happening.

The findings show that the main driver of  “polar amplification” – warming in excess of the global average – is shrinking ice cover, rather than increased cloudiness or changes in ocean and atmospheric circulation.  The study’s findings also suggest that current forecasts underestimate the degree to which the polar region could heat up in the future.

A new report from the U.S. Environmental Protection Agency titled Climate Change Indicators in the U.S. states the extent of Arctic sea ice in 2009 was 24% below the 1979 to 2000 historical average. The area covered by ice is typically smallest in September, after the summer melting season. September 2007 had the least ice of any year on record, followed by 2008 and 2009.

The National Snow and Ice Data Center reports Arctic sea ice running only a bit below the 1979-2000 average – so far.

But the ice is thin, and it’s still early.

Here’s the abstract of the Screen  & Ian Simmonds study, published this week in the journal Nature:

The rise in Arctic near-surface air temperatures has been almost twice as large as the global average in recent decades — a feature known as ‘Arctic amplification’. Increased concentrations of atmospheric greenhouse gases have driven Arctic and global average warming; however, the underlying causes of Arctic amplification remain uncertain. The roles of reductions in snow and sea ice cover and changes in atmospheric and oceanic circulation cloud cover and water vapour are still matters of debate. A better understanding of the processes responsible for the recent amplified warming is essential for assessing the likelihood, and impacts, of future rapid Arctic warming and sea ice loss. Here we show that the Arctic warming is strongest at the surface during most of the year and is primarily consistent with reductions in sea ice cover. Changes in cloud cover, in contrast, have not contributed strongly to recent warming. Increases in atmospheric water vapour content, partly in response to reduced sea ice cover, may have enhanced warming in the lower part of the atmosphere during summer and early autumn. We conclude that diminishing sea ice has had a leading role in recent Arctic temperature amplification. The findings reinforce suggestions that strong positive ice–temperature feedbacks have emerged in the Arctic increasing the chances of further rapid warming and sea ice loss, and will probably affect polar ecosystems, ice-sheet mass balance and human activities in the Arctic.

Between 1961 and 1985, the ice cap grew in some years and shrank in others, resulting in an overall loss of mass. A paper published in the March edition of the journal Arctic finds a steady decline in ice volume and area began in 1985, a decline that is now accelerating.

The High Arctic is essentially a desert with low rates of annual precipitation. There is little accumulation of snow in the winter; and cool summers, with temperatures at or below freezing, maintain snow and ice levels. Any increase of snow and ice takes years – and one warm summer can wipe out many years of growth. Though the accelerated melting trend began in 1985, the last decade has seen four years with unusually warm summers: 2001, 2005, 2007 and 2008.

Another recent study finds that ice loss from the Greenland ice sheet, which has been increasing during the past decade over its southern region, is now moving up its northwest coast. The research indicates the ice-loss acceleration began moving up the northwest coast of Greenland starting in late 2005.

The AGU press release quotes study co-author John Wahr:

When we look at the monthly values from GRACE, the ice mass loss has been very dramatic along the northwest coast of Greenland. This is a phenomenon that was undocumented before this study. Our speculation is that some of the big glaciers in this region are sliding downhill faster and dumping more ice in the ocean.

and co-author Isabella Velicogna:

These changes on the Greenland ice sheet are happening fast, and we are definitely losing more ice mass than we had anticipated. We also are seeing this trend in Antarctica, a sign that warming temperatures really are having an effect on ice in Earth’s cold regions.

During March 2010, ice extent grew at an average of 13,200 square kilometers (5100 square miles) per day. Usually there is a net loss of ice through the month.

The late-season growth was driven mainly by cold weather and winds from the north over the Bering and Barents Seas. However, temperatures over the central Arctic Ocean remained above normal and the winter ice cover remained young and thin compared to previous years.

Ice extent was above normal in the Bering Sea and Baltic Sea, but remained below normal over much of the Atlantic sector of the Arctic, including the Baffin Bay, and the Canadian Maritime Provinces seaboard. Extent in other regions was near average.

NSIDC cautions that the extent of late-season ice doesn’t mean much for ice cover this coming summer.

The late date of the maximum extent, though of special interest this year, is unlikely to have an impact on summer ice extent. The ice that formed late in the season is thin, and will melt quickly when temperatures rise.

This winter saw some replenishment of thicker, multiyear ice, as less ice moved out of the Arctic due to a strong negative Arctic Oscillation.  However, this replenishment consists primarily of younger, two- to three-year-old multiyear ice; the oldest, and thickest multiyear ice has continued to decline.

Although thickness plays an important role in ice melt, summer ice conditions will also depend strongly on weather patterns through the melt season.