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• Tuesday, July 1, 2008 04:20 PM

  National Snow and Ice Data Center: "Arctic Ice Still On Track For Extreme Melt"

  manacker: "Arctic sea ice extent for May 2008 was 13.18 million square kilometers, reaching the same level as in May 1989."

  Right. And per the same National Snow and Ice Data Center (NSIDC) graph that you cited here:

  http://nsidc.org/data/seaice_index/images/n_plot_hires.png

  May 1989 was the lowest year on record since this data was collected up to that year, an has been superceeded at least twice since.

  Far more importantly, the general trend since ice extant data has been collected has been a clear decrease of ice extant over time.

  manacker: "The linear average rate of decline is 3.0%/decade (over the 30-year period since measurements have started). If the decline continues at this rate, it will take 330 years for the entire Arctic sea ice to disappear."

  Yes - that is the trend.

  manacker: "The most recent decline has however not continued at the 3.0%/decade rate, since the May 2008 extent is back to the May 1989 extent (i.e. zero net decline in 19 years)."

  manacker: Do you have a substantive background in statistical trend analysis? Because if so, then not only would you know that your statement here is misleading disinformation, but you'd be disingenuous here too. Trend rates are not calculated by picking one low point out of many on a graph and then extrapolating a trend line from it, they are instead calculated by taking the data set and doing a linear regression analysis on it to determine the degree and correlation of the trend. What you are doing here instead is misleading cherry-picking.

  In other words: your statement there is bullshit, manacker.

  Per the same National Snow and Ice Data Center (NSIDC):

  June 3, 2008

  Arctic sea ice still on track for extreme melt

  Daily ice extents in May continued to be below the long-term average and approached the low levels seen at this time last year. As discussed in our last posting, the spring ice cover is thin. One sign of thin and fairly weak ice is the formation of several polynyas in the ice pack. ...

  Overview of conditions

  Arctic sea ice extent for May stood at 13.18 million square kilometers (5.09 million square miles), which is 0.28 million square kilometers (0.11 million square miles) greater than May 2007, but is still 0.42 million square kilometers (0.16 million square miles) less than the 1979 to 2000 average for the month.

  Conditions in context

  Although ice extent is slightly greater than this time last year, the average decline rate through the month of May was 8,000 square kilometers per day (3,000 square miles per day) faster than last May. Ice extent as the month closed approached last May’s value.

  Average Arctic Ocean surface air temperatures in May were generally higher than normal. While anomalies were modest (+1 to 3 degrees Celsius, +2 to 5 degrees Fahrenheit) over most of the region, temperatures over the Baffin Bay region were as much as 6 degrees C (11 degrees F) above normal. ...

  Multi-year ice continues to be low

  The relative lack of thick, resilient multi-year ice in the Arctic discussed in earlier postings finds further support in the latest analysis from the United States National Ice Center (NIC). NIC uses a variety of satellite imagery, expert analysis, and other information to provide information on the amount and quality of sea ice for ships operating in the Arctic. NIC scientist Todd Arbetter suggests that much of the first-year ice is likely to melt by the end of summer, saying that despite the total ice extent appearing normal, the relative amount of multi-year ice going into this summer is very low when compared to climatological averages. NIC has found that the relative fraction of multi-year ice in the central Arctic has plummeted since the mid-1990s, creating an Arctic prone to increased melt in summer. Arbetter said, “This may be a primary reason for record summertime minimums in recent years.” ...

  Thinner ice already showing weakness

  As mentioned, the thin ice that covers much of the Arctic Ocean is showing signs of early breakup, with large polynyas off the coast of Alaska, the Canadian Archipelago, and Baffin Bay. Coastal polynyas are not unusual, at this time of year, but the polynyas we are currently seeing appear larger and more numerous than usual. This is partly because of the thinner, weaker ice cover.

  Thorsten Markus at the NASA Goddard Space Flight Center has noted the size of the North Water polynya at the northern end of Baffin Bay, which typically forms in May. The polynya is much larger than normal, possibly nearing its largest area on record.

  Inuit report that sea ice is starting to break up near Baffin Bay much earlier than normal this year. They have observed wide cracks in the ice already forming, according to NSIDC scientist Shari Gearheard, who lives and works in the Baffin Island hamlet of Clyde River.

  Polynyas are a source of heat for the atmosphere in spring; in summer, however, they are large absorbers of solar energy. Resultant warm ocean surface waters then eat away at the ice edge, accelerating melt.

  http://nsidc.org/arcticseaicenews/index.html

  —Publicola Read Publicola's other letters
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