Scientists have been measuring sea ice very carefully since 1979. Prior to that, there are estimates that are of varying degrees of usefulness. I know for a fact that many New England lighthouses were attached to land by winter-long ice in places that have not had sea ice in any living person’s memory, and there are similar bits and pieces of historical data suggesting that sea ice was once much more extensive in the Northern Hemisphere than at present.

Since 1979 there have been three years in which Arctic sea ice reached a rather alarming minimum size prior to reforming. We are in one of those years now.

i-113cd17635f7a7fd6159abdff3c729a2-20100915_Figure1-thumb-500x596-55890.png

Daily Arctic sea ice extent on September 10, 2010 was 4.76 million square kilometers (1.84 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. (From the NCIDC)

On September 10, 2010 sea ice extent dropped to 4.76 million square kilometers (1.84 million square miles). This appears to have been the lowest extent of the year; sea ice has now begun its annual cycle of growth.

The 2010 minimum ice extent is the third-lowest recorded since 1979.

This year is the third time since data have been collected that ice is measured at less than 5×106 square kilometers. The other times have all been within the last four years. In other words, the typical extent of Arctic sea ice is now much smaller than it was previously, a strong indicator and effect of global warming.

More details are here.

Comments

  1. #1 Mu
    September 16, 2010

    Next you’re going to tell us there’s something like global warming.

  2. #2 Quietmarc
    September 16, 2010

    If there’s less ice and things are warming up, why do stories like this send chills down my spine?

  3. #3 Piccamo
    September 16, 2010

    Sounds like a left-wing conspiracy to convert us into European style athiest socialists to me. Until someone with some credibility like Rush Limbaugh or Papa Bear O’Reilly steps up to do a documentary (with much better production values than whatever it was Gore put out), I will continue to be skeptical!

    /sarcasm

  4. #4 MadScientist
    September 16, 2010

    @Quietmarc: Well, there’s ice and ice and ice and although many processes associated with the formation and thawing are known, constraining the contributions of various processes and trying to model what’s going on (and to get to the point where meaningful predictions can be made) remains a huge task. Just a little over 100 years ago the Norwegian Roald Amundsen made the first contemporary (and one of the very few) ship voyages through the Northwest Passage, so we know that 100 years ago it was clear enough of ice to navigate and we also know that for most of the past 100 years it was not navigable.

  5. #5 Ben W
    September 17, 2010

    Yeah, but didn’t it take Roald Amundsen three winters to get through the Northwest Passage? I think the take away-message is that while it was occasionally clear in the past, it’s only now starting to become consistently navigable.

  6. #6 Elli Betty
    September 20, 2010

    It may due to the global warming, It is high time to take the concrete steps before it is too late.

  7. #7 Sharice Pasche
    September 20, 2010

    Global warming is taking its toll on the world climate. If this continues, then all the low lying islands and countries will submerge under water.
    http://noxedgereviews.org/

  8. #8 Greg Laden
    April 21, 2011

    This post is closed to comments due to spam from homeopaths. If you have a comment you’d like to leave and you are for real, email me (see “contact” page). Thanks.

    GTL

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