The graph above shows daily Arctic sea ice extent as of July 5, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. (National Snow and Ice Data Center)

It’s that time of year again, when the air in the Mid-Atlantic feels more like soup, afternoon thunderstorms arrive with regularity, and when news of sweeping changes in a faraway region – the Arctic – tends to pick up. We’re now well into the seasonal Arctic sea ice melt season, and so far, sea ice has been tracking near or below the record low extent reached in 2007, when both the famed Northwest Passage and the Northern Sea Route were open for a time.

The precipitous decline of Arctic sea ice during the past 30 years of the satellite record (and longer, when other data is taken into consideration) has been one of the most striking manifestations of global climate change, and it’s ushering in a new era of resource development, competition, and cooperation in the Far North.

Evidence also indicates that as the sea ice cover shrinks; weather patterns within and beyond the immediate Arctic Circle have been changing as well – more on this in a minute.

According to one measure of sea ice coverage – average ice extent – the decline in ice cover appears to be occurring slightly faster so far this year than in June 2007, but it’s not clear that it will wind up below the extent measured in September 2007.

Sea ice extent from June 2002 to the present. (Japan Aerospace Exploration Agency (JAXA))

The most recent sea ice outlook, issued earlier this month by an assortment of scientific researchers using methods ranging from sophisticated computer models to simple guesswork, calls for sea ice extent to wind up above that of the 2007 record melt, but below last year’s level, once the current melt season ends sometime in September or early October.

The median value of sea ice extent called for in the June sea ice outlook is 4.7 million square kilometers, which matches the 2008 level, and is below the last two years. The outlook includes this important sentence to keep in mind when you hear about one year being slightly below the previous year, since the most important thing is the long-term trend, not year-to-year variations (even though that’s what makes news):

“It is important to note for context that all 2011 estimates are well below the 1979–2007 September climatological mean of 6.7 million square kilometers.”

The outlook will be updated each month during the summer, and at the end of the melt season researchers will analyze how well their predictions fared compared to actual conditions.

Distribution of individual Pan-Arctic Outlook values (June Report) for September 2011 sea ice extent. Interestingly, one of the contributors to the outlook were readers of the climate skeptic website Watts Up With That , who submitted a sea ice forecast that came from of a readers’ poll (not exactly the most scientifically rigorous approach). The majority vote: “Greater than 5.5 million square kilometers.” (National Snow and Ice Data Center)

The weather is the most significant variable that will influence the 2011 melt season from here on out. Recent summers have featured an unusual weather pattern that promotes significant drops in sea ice extent, known as the “Arctic Dipole Anomaly.” According to the National Snow and Ice Data Center (NSIDC) in Boulder, Colo., there were signs of that pattern during May, but it was not clear that it would take shape during this month or through the rest of the summer.

The Dipole Anomaly is characterized by anomalously high pressure over the northern Beaufort Sea, north of Alaska, and unusually low pressure centered over the Kara Sea along the Eurasian Coast. The pattern promotes southerly winds to blow off the Siberian coast, which pushes sea ice away from the shore, promoting ice dispersal and faster melting.

The Dipole Anomaly pattern also promotes more sea ice transport out of the Arctic through Fram Strait, which lies between Canada and Greenland. In recent summers that strait has turned into an expressway for sea ice fleeing the Arctic Ocean, destined to melt in the North Atlantic.

Just as global average temperatures are not rising from one year to the next, but instead are increasing over a longer period of time, sea ice is not dropping precipitously from one melt season too the next. In fact, studies show that as overall sea ice cover declines, it may become more prone to large shifts from weather conditions.

Researchers are trying to answer the question of how stable the sea ice cover currently is, and when the day may come when the Arctic Ocean is free of ice during the summer, as many studies project for sometime during this century. As NSIDC states:

Climate models suggest periods of stability (with variations around a stationary summer mean extent) with intermittent years of rapid reductions in ice extent as the Arctic warms.
While summer ice extent has been clearly shrinking over the years, in any given summer its extent may vary because of the weather. Over the thirty-year satellite record, sea ice has shown a dramatic decline. In September, generally the lowest month of the year for Arctic sea ice extent, sea ice has dropped by more than 30 percent since 1979. That decline doesn’t run in a straight line, however, with each year falling a little lower than the last. Instead the ice extent dances around that downward trend line, buoyed by cold weather or winds that spread the ice pack apart, or forced downwards by sunny warm weather and winds that push the ice together.

When writing about Arctic sea ice decline I am often confronted by the question: Why should ordinary Americans, who aren’t planning on exploring the North Pole anytime soon, care about what’s going on up there?

In addition to the fact that what’s happening in the Far North is a symptom of the much larger problem of global climate change, there’s are major national security challenges associated with an increasingly ice-free ocean that had long been considered inaccessible, except by submarines. Also relevant to most Americans is emerging research showing that sea ice loss may have contributed to recent unusual weather events in the U.S. (such as “Snowmageddon”).

A fact sheet on the NSIDC website provides a solid rundown of the research showing possible links between declining sea ice cover and altered storm tracks in the Northern Hemisphere. This statement by Jennifer Francis of Rutgers University, who has published recent research on this subject, caught my attention.

“We do not know if Arctic change is responsible for record cold outbreaks in Europe the past two years or the heavy snowstorms along the U.S. East Coast. All we know right now is that the behavior fits the current theory.”