Last week, the National Snow and Ice Data Center came out with the estimate that we did not quite ​set a record for the minimum extent of Arctic sea this year. Rather, 2011 seems to have come in a slight second to 2007.

However, another scientific group does claim that we've hit a new record. Who's right?

I don't know, but I don't think either bit of news is the most important thing to focus on. For as Skeptical Science points out, we also just learned that total sea ice volume reached a new low in 2010 (wonky hide-the-punchline paper here). And that is, to my mind, a much bigger deal than what total sea ice extent is doing on a year by year basis.

Remember, extent is a measure of area covered, and volume is a measure of total ice mass. (More clarification here.)

There is a strong case that volume matters more, because extent can be misleading. Why?

In my last post, I discussed how the increasing risk of devastating heat waves—unlike the worsening of tornadoes—is definitely a phenomenon we can link to global warming. And now, as summer plods on, it’s time to begin paying attention to another one: the continuing decline of Arctic sea ice.

The extent of ice covering the Arctic has been declining for decades, and reached a record low in September of 2007, nearly 40 percent below its long term average. This wasn’t solely the product of global warming—weather patterns also have a lot to do with ice extent, and they contributed to the 2007 record. 

Nevertheless, much like the worsening of heat waves, Arctic ice decline is one of the most obvious  impacts of global warming—and this year, it’s possible that Arctic ice extent might reach a minimum even lower than it did in 2007.

Update: NSIDC pinpoints Sept. 19 as date of least Arctic ice extent in 2010

Arctic Sea Ice Extent, which the National Snow and Ice Data Center (NSIDC) in Boulder, Co., announced had reached its annual minimum on Sept. 10, has now slipped even further, to a point that could be below the 2008 minimum. That would make this the second lowest summer ice cover in recorded history.

“It’s awfully close (to the 2008 low),” NSIDC research scientist Dr. Walt Meier said on Wednesday (Sept. 22, 2010). “And even though the air temperatures are getting colder, the ocean has a lot of heat in it and can continue to melt ice.”

Meier acknowledged that the NSIDC jumped the gun in announcing the apparent annual minimum. The ice extent had been increasing for three consecutive days and the scientists assumed the season had turned. But much of the ice is broken up and thin, conditions that mean “it doesn’t take a lot to get late season melting,” Meier said.

Ice watchers may be more concerned, however, by the inset Polar Science Center graph of ice volume, which shows that the total amount of ice (as differentiated from the extent of the Arctic ice cover) has dropped off a cliff.

Those in search of clear, accessible explanations that debunk the latest denier talking points will be delighted to discover Wellesley College postdoc Alden Griffith and his website, Fool Me Once.

The site’s subtitle is perfect and perfectly accurate - “What climate change deniers fear most: thorough explanations” - and Griffith provides two such explanations, so far. They’re in the form of PowerPoint-style presentations with a voice-over and they categorically destroy the notion that (in Christopher Monckton’s mendacious phrase) “Arctic sea ice is just fine” or that “global warming has stopped.” I only wish that I had wallet-sized copies of Griffith’s graphs so I could flash them at annoying relatives who parrot these lines as if they have some validity.

Arctic ice has maxed out for the year and is starting its slow melt into summer in much worse shape than normal, according to the National Snow and Ice Data Centre.

If you look only at the extent of Arctic sea ice, things are not as bad as they have been in recent years. Ice cover is five per cent higher this year than in the record low 2006, even if it is four per cent lower than the 1979 to 2000 average.

 

But ice thickness is another story, and that seems to be all bad news.

There remains a lot of messaging and spin running rampant online over Washington Post colmunist George Will’s misguided and baseless claims that sea ice coverage is similar to 1979.

DeSmog writer Mitchell Anderson has been covering this baffling story for us and doing a great job, but I wanted to provide a few of the sources that have done a particularly good job at highlighting just how much sea ice we have lost since the 1970’s when we first started recording such things. 

These source easily and compellingly explain away George Will’s incorrect claim that sea ice coverage is the same today as it was in 1979.

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1. You can watch the extent of Arctic Ice melt decreasing over time. Here’s a great satellite image time series video done by NASA that shows the year-to-year melting of sea ice in the Arctic. I don’t know how anyone could argue that sea ice in the Arctic is the same as it was in 1979 after watching this video: