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	<title>Comments on: Arctic Ice Extent Discrepancy: NSIDC versus Cryosphere Today</title>
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	<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/</link>
	<description>The world&#039;s most viewed site on global warming and climate change</description>
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		<title>By: Robert Marston</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-39247</link>
		<dc:creator><![CDATA[Robert Marston]]></dc:creator>
		<pubDate>Sun, 14 Sep 2008 20:39:28 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-39247</guid>
		<description><![CDATA[We are currently, according to Cryosphere Today data, at last year&#039;s record low sea ice measurement. Any further melt, at all, will result in a new record.]]></description>
		<content:encoded><![CDATA[<p>We are currently, according to Cryosphere Today data, at last year&#8217;s record low sea ice measurement. Any further melt, at all, will result in a new record.</p>
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		<title>By: Hello</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-37850</link>
		<dc:creator><![CDATA[Hello]]></dc:creator>
		<pubDate>Tue, 09 Sep 2008 17:51:47 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-37850</guid>
		<description><![CDATA[I dont know about you guys but i dont belived in this post.

Here are a NASA link which shows that sea ice retreated enough to create open waters all the way around the northern ice pack.

http://www.nasa.gov/mission_pages/IPY/multimedia/ipyimg_20080909.html

You articles shows sattelite images but are they real? Do you have real links for that images ? Can you post them here in order to confirm your theory ?]]></description>
		<content:encoded><![CDATA[<p>I dont know about you guys but i dont belived in this post.</p>
<p>Here are a NASA link which shows that sea ice retreated enough to create open waters all the way around the northern ice pack.</p>
<p><a href="http://www.nasa.gov/mission_pages/IPY/multimedia/ipyimg_20080909.html" rel="nofollow">http://www.nasa.gov/mission_pages/IPY/multimedia/ipyimg_20080909.html</a></p>
<p>You articles shows sattelite images but are they real? Do you have real links for that images ? Can you post them here in order to confirm your theory ?</p>
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		<title>By: Arctic Ice Growth, 2008 - How Much? &#171; Watts Up With That?</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-35295</link>
		<dc:creator><![CDATA[Arctic Ice Growth, 2008 - How Much? &#171; Watts Up With That?]]></dc:creator>
		<pubDate>Sun, 31 Aug 2008 15:45:44 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-35295</guid>
		<description><![CDATA[[...] my most recent article in The Register, and also posted here on WUWT, I incorrectly speculated that NSIDC graphs appeared to show less growth in Arctic ice extent than [...]]]></description>
		<content:encoded><![CDATA[<p>[...] my most recent article in The Register, and also posted here on WUWT, I incorrectly speculated that NSIDC graphs appeared to show less growth in Arctic ice extent than [...]</p>
]]></content:encoded>
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		<title>By: Timothy Birdnow &#187; Correction on NSIDC Graph</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-34999</link>
		<dc:creator><![CDATA[Timothy Birdnow &#187; Correction on NSIDC Graph]]></dc:creator>
		<pubDate>Sat, 30 Aug 2008 14:06:49 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-34999</guid>
		<description><![CDATA[[...] and I found out about it via Tom Nelson (a very reliable source). It turns out that the author has revised his analysis based on conversations with the NSIDC; the differences in the photographs he used to determine ice [...]]]></description>
		<content:encoded><![CDATA[<p>[...] and I found out about it via Tom Nelson (a very reliable source). It turns out that the author has revised his analysis based on conversations with the NSIDC; the differences in the photographs he used to determine ice [...]</p>
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		<title>By: Fred Houpt</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-34543</link>
		<dc:creator><![CDATA[Fred Houpt]]></dc:creator>
		<pubDate>Thu, 28 Aug 2008 17:19:35 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-34543</guid>
		<description><![CDATA[I just read this in today&#039;s English internet Der Spiegel:

http://www.spiegel.de/international/world/0,1518,574815,00.html

I had to laugh.  I read this part: &quot;Many, in fact, have begun talking about an Arctic Ocean completely free of ice. The way things look now, such a scenario is not in the immediate future, but a sad, new record may indeed by set this year: The tiniest quantity of Arctic ice since scientists first started taking measurements. The Arctic melting season has another three weeks to go before the flat angle of the sun&#039;s rays mark the onset of winter.&quot;

I find the unsupported claim that the Arctic has not seen such a small ice coverage outrageous.  No reference to any study whatsoever.  In my view, this is the opinion of the writer but it comes across sounding as if based on known facts.  

Another thing that I noted missing was the fact that the waters all along the passageways are often shallow and littered with hull-destroying boulders just waiting for a deep draft tanker to troll by.  These waters have NEVER ever been dredged and to think that they will raises the big question of who will pay the astronomical price?  Canada?  Not bloody likely.  I do not know how the ice breakers make their way through without hitting rocks? Perhaps they are double hull lined, go slowly and have advanced sonar to make sure they avoid trouble?  

Finally, what I found ridiculous is the premise that at the last days of August, when this current ice free/ice thin environment has shown up will somehow in future years provide a workable shortcut for big ships? I mean, what are they thinking?  The ships would have to enter the northwest passage at a time when the vast majority is still ice covered and wait until it breaks up.  If it takes till the end of August, what are the ships going to do? Wait it out up in northern Hudson&#039;s Bay? It makes no sense to start planning to use the passage because as I say it is a far too short period and the lane ways are not dredged.  For me the use of the NWP is still a far off dream.]]></description>
		<content:encoded><![CDATA[<p>I just read this in today&#8217;s English internet Der Spiegel:</p>
<p><a href="http://www.spiegel.de/international/world/0,1518,574815,00.html" rel="nofollow">http://www.spiegel.de/international/world/0,1518,574815,00.html</a></p>
<p>I had to laugh.  I read this part: &#8220;Many, in fact, have begun talking about an Arctic Ocean completely free of ice. The way things look now, such a scenario is not in the immediate future, but a sad, new record may indeed by set this year: The tiniest quantity of Arctic ice since scientists first started taking measurements. The Arctic melting season has another three weeks to go before the flat angle of the sun&#8217;s rays mark the onset of winter.&#8221;</p>
<p>I find the unsupported claim that the Arctic has not seen such a small ice coverage outrageous.  No reference to any study whatsoever.  In my view, this is the opinion of the writer but it comes across sounding as if based on known facts.  </p>
<p>Another thing that I noted missing was the fact that the waters all along the passageways are often shallow and littered with hull-destroying boulders just waiting for a deep draft tanker to troll by.  These waters have NEVER ever been dredged and to think that they will raises the big question of who will pay the astronomical price?  Canada?  Not bloody likely.  I do not know how the ice breakers make their way through without hitting rocks? Perhaps they are double hull lined, go slowly and have advanced sonar to make sure they avoid trouble?  </p>
<p>Finally, what I found ridiculous is the premise that at the last days of August, when this current ice free/ice thin environment has shown up will somehow in future years provide a workable shortcut for big ships? I mean, what are they thinking?  The ships would have to enter the northwest passage at a time when the vast majority is still ice covered and wait until it breaks up.  If it takes till the end of August, what are the ships going to do? Wait it out up in northern Hudson&#8217;s Bay? It makes no sense to start planning to use the passage because as I say it is a far too short period and the lane ways are not dredged.  For me the use of the NWP is still a far off dream.</p>
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		<title>By: Rick</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-34313</link>
		<dc:creator><![CDATA[Rick]]></dc:creator>
		<pubDate>Wed, 27 Aug 2008 18:14:48 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-34313</guid>
		<description><![CDATA[http://nsidc.org/images/arcticseaicenews/200807_Figure1.png
http://nsidc.org/images/arcticseaicenews/20080717_Figure1.png
http://nsidc.org/images/arcticseaicenews/20080801_Figure1.png


Interesting...as long as the sea ice matched the &quot;median&quot; line, it was called the &quot;median&quot;.  As soon as the ice was less than that line, it is called &quot;normal&quot;.

So is the melting sea ice below &quot;median&quot; or is it below &quot;normal&quot;?  And is it &quot;normal&quot; to be below &quot;median&quot;?

Wouldn&#039;t it be more scientific to be more constant with their statistical terms?  

Links to the maps where I noticed the change.]]></description>
		<content:encoded><![CDATA[<p><a href="http://nsidc.org/images/arcticseaicenews/200807_Figure1.png" rel="nofollow">http://nsidc.org/images/arcticseaicenews/200807_Figure1.png</a><br />
<a href="http://nsidc.org/images/arcticseaicenews/20080717_Figure1.png" rel="nofollow">http://nsidc.org/images/arcticseaicenews/20080717_Figure1.png</a><br />
<a href="http://nsidc.org/images/arcticseaicenews/20080801_Figure1.png" rel="nofollow">http://nsidc.org/images/arcticseaicenews/20080801_Figure1.png</a></p>
<p>Interesting&#8230;as long as the sea ice matched the &#8220;median&#8221; line, it was called the &#8220;median&#8221;.  As soon as the ice was less than that line, it is called &#8220;normal&#8221;.</p>
<p>So is the melting sea ice below &#8220;median&#8221; or is it below &#8220;normal&#8221;?  And is it &#8220;normal&#8221; to be below &#8220;median&#8221;?</p>
<p>Wouldn&#8217;t it be more scientific to be more constant with their statistical terms?  </p>
<p>Links to the maps where I noticed the change.</p>
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		<title>By: Phil.</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33724</link>
		<dc:creator><![CDATA[Phil.]]></dc:creator>
		<pubDate>Mon, 25 Aug 2008 16:52:27 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33724</guid>
		<description><![CDATA[Sorry image tag didn&#039;t work, I was referring to this graph:
http://www.arcus.org/search/seaiceoutlook/report_june.php]]></description>
		<content:encoded><![CDATA[<p>Sorry image tag didn&#8217;t work, I was referring to this graph:<br />
<a href="http://www.arcus.org/search/seaiceoutlook/report_june.php" rel="nofollow">http://www.arcus.org/search/seaiceoutlook/report_june.php</a></p>
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		<title>By: Phil.</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33711</link>
		<dc:creator><![CDATA[Phil.]]></dc:creator>
		<pubDate>Mon, 25 Aug 2008 15:58:55 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33711</guid>
		<description><![CDATA[&lt;em&gt;Demesure (06:58:19) :

You’re correct dhogaza, we should just look at graphs instead of relying on AGW experts’ predictions. For 2008’s minimum extent, they mostly (9 out 17 teams) predict a lower or equal extent compared to the 2007 low record.&lt;/em&gt;


&quot;Of the 17 responses, all suggest that the extent will remain lower than the historical average (i.e., mean 1979–2000 September values) of 7.0 million square kilometers.&quot;
All correct.

&quot;Five (5) responses suggested a less dramatic loss than in 2007 (i.e., 4.3 million square kilometers) and closer to the pre-2007 long-term trend of approximately 10% loss per decade.&quot;
Too conservative, already passed.


&quot;Five (5) anticipate a repeat of the dramatic loss of 2007.&quot;
They look like being on the money.



&quot;Four (4) suggest a loss even greater than that experienced in 2007.&quot;
They could still be right but it will be close to the wire.



&quot;Three (3) give more detailed reports on regional trends.&quot;
Didn&#039;t play the game.

Reading the more detailed report yielded this .  The current value is 5.4 and still dropping so the more conservative predictions have already been passed, it looks like it will end up close to the average of the predictions.  Not bad since most of the melt has occurred since those predictions were made.]]></description>
		<content:encoded><![CDATA[<p><em>Demesure (06:58:19) :</p>
<p>You’re correct dhogaza, we should just look at graphs instead of relying on AGW experts’ predictions. For 2008’s minimum extent, they mostly (9 out 17 teams) predict a lower or equal extent compared to the 2007 low record.</em></p>
<p>&#8220;Of the 17 responses, all suggest that the extent will remain lower than the historical average (i.e., mean 1979–2000 September values) of 7.0 million square kilometers.&#8221;<br />
All correct.</p>
<p>&#8220;Five (5) responses suggested a less dramatic loss than in 2007 (i.e., 4.3 million square kilometers) and closer to the pre-2007 long-term trend of approximately 10% loss per decade.&#8221;<br />
Too conservative, already passed.</p>
<p>&#8220;Five (5) anticipate a repeat of the dramatic loss of 2007.&#8221;<br />
They look like being on the money.</p>
<p>&#8220;Four (4) suggest a loss even greater than that experienced in 2007.&#8221;<br />
They could still be right but it will be close to the wire.</p>
<p>&#8220;Three (3) give more detailed reports on regional trends.&#8221;<br />
Didn&#8217;t play the game.</p>
<p>Reading the more detailed report yielded this .  The current value is 5.4 and still dropping so the more conservative predictions have already been passed, it looks like it will end up close to the average of the predictions.  Not bad since most of the melt has occurred since those predictions were made.</p>
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		<title>By: Demesure</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33691</link>
		<dc:creator><![CDATA[Demesure]]></dc:creator>
		<pubDate>Mon, 25 Aug 2008 13:58:19 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33691</guid>
		<description><![CDATA[&quot;Or just look at the NSIDC graph…&quot;

You&#039;re correct dhogaza, we should just look at graphs instead of relying on AGW experts&#039; predictions. For 2008&#039;s minimum extent, they mostly (9 out 17 teams) predict a lower or equal extent compared to the 2007 low record.
And that&#039;s a &quot;prediction&quot; just ... 2 months ago (June report) :
http://www.arcus.org/search/seaiceoutlook/report_june.php]]></description>
		<content:encoded><![CDATA[<p>&#8220;Or just look at the NSIDC graph…&#8221;</p>
<p>You&#8217;re correct dhogaza, we should just look at graphs instead of relying on AGW experts&#8217; predictions. For 2008&#8242;s minimum extent, they mostly (9 out 17 teams) predict a lower or equal extent compared to the 2007 low record.<br />
And that&#8217;s a &#8220;prediction&#8221; just &#8230; 2 months ago (June report) :<br />
<a href="http://www.arcus.org/search/seaiceoutlook/report_june.php" rel="nofollow">http://www.arcus.org/search/seaiceoutlook/report_june.php</a></p>
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		<title>By: dhogaza</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33398</link>
		<dc:creator><![CDATA[dhogaza]]></dc:creator>
		<pubDate>Sat, 23 Aug 2008 18:28:32 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33398</guid>
		<description><![CDATA[That&#039;s because there has BEEN as large a melt this year as last.  Remember that cold winter you guys were all excited about, and the recovery of arctic ice that y&#039;all were going on about?  Remember you guys being so excited that ice extent at the beginning of the melt season was greater than in 2007?

Yes, the ice extent up to this point in 2008, is about 5% higher than in 2007.  But since there was more ice to begin with, the amount that&#039;s melted this year is about the same as last year (thus far).

Nothing odd about that.  You don&#039;t even need algebra to figure it out, nor multiplication and division.  Simple subtraction is sufficient.

Or just look at the NSIDC graph...]]></description>
		<content:encoded><![CDATA[<p>That&#8217;s because there has BEEN as large a melt this year as last.  Remember that cold winter you guys were all excited about, and the recovery of arctic ice that y&#8217;all were going on about?  Remember you guys being so excited that ice extent at the beginning of the melt season was greater than in 2007?</p>
<p>Yes, the ice extent up to this point in 2008, is about 5% higher than in 2007.  But since there was more ice to begin with, the amount that&#8217;s melted this year is about the same as last year (thus far).</p>
<p>Nothing odd about that.  You don&#8217;t even need algebra to figure it out, nor multiplication and division.  Simple subtraction is sufficient.</p>
<p>Or just look at the NSIDC graph&#8230;</p>
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		<title>By: hunter</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33376</link>
		<dc:creator><![CDATA[hunter]]></dc:creator>
		<pubDate>Sat, 23 Aug 2008 15:12:58 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33376</guid>
		<description><![CDATA[Your explanation of your reconciliation of the two data sources is being used by AGW believers as an admission that inspite of the facts, there is as large a melt this year as last.]]></description>
		<content:encoded><![CDATA[<p>Your explanation of your reconciliation of the two data sources is being used by AGW believers as an admission that inspite of the facts, there is as large a melt this year as last.</p>
]]></content:encoded>
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		<title>By: Duae Quartunciae</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33370</link>
		<dc:creator><![CDATA[Duae Quartunciae]]></dc:creator>
		<pubDate>Sat, 23 Aug 2008 14:12:22 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33370</guid>
		<description><![CDATA[I&#039;m going to pull my head back in...

dipole had an excellent way to test my hypothesis, and it doesn&#039;t seem to work.

Basically, there is no discontinuity I can see. The data in 2007 is closer to the 50% ice extent; but this may just be a co-incidence. I&#039;m now really curious; but it could be a problem in my own maths. I&#039;ll double check... no assurance I can come back to this soon, sorry.]]></description>
		<content:encoded><![CDATA[<p>I&#8217;m going to pull my head back in&#8230;</p>
<p>dipole had an excellent way to test my hypothesis, and it doesn&#8217;t seem to work.</p>
<p>Basically, there is no discontinuity I can see. The data in 2007 is closer to the 50% ice extent; but this may just be a co-incidence. I&#8217;m now really curious; but it could be a problem in my own maths. I&#8217;ll double check&#8230; no assurance I can come back to this soon, sorry.</p>
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		<title>By: dipole</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33326</link>
		<dc:creator><![CDATA[dipole]]></dc:creator>
		<pubDate>Sat, 23 Aug 2008 04:24:27 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33326</guid>
		<description><![CDATA[Duae Quartunciae (16:10:29) says:

&lt;i&gt;I’m going to stick my neck out...&lt;/i&gt;

Excellent piece of calculation DQ. If you are correct there should be a sudden and physically implausible jump in pixel count at some point in the UIUC image sequence.]]></description>
		<content:encoded><![CDATA[<p>Duae Quartunciae (16:10:29) says:</p>
<p><i>I’m going to stick my neck out&#8230;</i></p>
<p>Excellent piece of calculation DQ. If you are correct there should be a sudden and physically implausible jump in pixel count at some point in the UIUC image sequence.</p>
]]></content:encoded>
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		<title>By: Duae Quartunciae</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33274</link>
		<dc:creator><![CDATA[Duae Quartunciae]]></dc:creator>
		<pubDate>Fri, 22 Aug 2008 23:23:03 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33274</guid>
		<description><![CDATA[Oops. On my previous comment, the 11-Aug-2007 above the second set of figures should be 11-Aug-2008]]></description>
		<content:encoded><![CDATA[<p>Oops. On my previous comment, the 11-Aug-2007 above the second set of figures should be 11-Aug-2008</p>
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		<title>By: Duae Quartunciae</title>
		<link>http://wattsupwiththat.com/2008/08/15/arctic-ice-extent-discrepancy-nsidc-versus-cryosphere-today/#comment-33272</link>
		<dc:creator><![CDATA[Duae Quartunciae]]></dc:creator>
		<pubDate>Fri, 22 Aug 2008 23:10:29 +0000</pubDate>
		<guid isPermaLink="false">http://wattsupwiththat.wordpress.com/?p=2260#comment-33272</guid>
		<description><![CDATA[I have a wild suggestion... 

In looking at this, I have taken NSIDC satellite data, and made my own images. I have projected them on the globe using a viewpoint above the pole which has a tangent to the surface at about latitude 27. This gives a very close match for the land masses.

Everything lines up very well indeed if I assume that the 2007 image is actually showing the area with ice cover at 50% or more; but the 2008 image is showing the area with ice cover at 30% or more. In particular, the NSIDC data allows me to construct an overlay of the 50% ice, or the 30% ice, and I get a very very close match with the UIUC images when I put them all together.

Here are the numbers, comparing UIUC images assuming this projection, the JAXA report of 15% ice cover or more, and my own simple area-weighted sum of extent from the NASA data (f13 channel, ~25km grid)

For 12-Aug-2007 
36683 pixels of ice on the UIUC image
4469014 sq km projected area
4201452 sq km at 50% or more, by simple count of NASA data
5057390 sq km at 30% or more, by simple count of NASA data
5679174 sq km at 15% or more, by simple count of NASA data
5421094 sq km at 15% or more, reported by JAXA

Some small differences are to be expected from processing differences; but basically the UIUC projected area lines up well with the extent of 50% ice, and JAXA lines up with the extent of 15% ice.

For 11-Aug-2007
47822 pixels of ice on the UIUC image
5882718 sq km projected area
4612971 sq km at 50% or more, by simple count of NASA data
5783576 sq km at 30% or more, by simple count of NASA data
6462289 sq km at 15% or more, by simple count of NASA data
6291563 sq km at 15% or more, reported by JAXA

This time the UIUC projected area lines up well with the extent of 30% ice, and JAXA still lines up with the extent of 15% ice.

Furthermore, I have projected the NASA data onto bitmaps, projected to align with UIUC images, and I get close agreement with the images using 50% for 2007 and 30% for 2008.

I&#039;m going to stick my neck out and predict that the UIUC archived images are actually showing the extent of ice at 50% or more, and that the recent UIUC images are showing the extent of ice at 30% or more.]]></description>
		<content:encoded><![CDATA[<p>I have a wild suggestion&#8230; </p>
<p>In looking at this, I have taken NSIDC satellite data, and made my own images. I have projected them on the globe using a viewpoint above the pole which has a tangent to the surface at about latitude 27. This gives a very close match for the land masses.</p>
<p>Everything lines up very well indeed if I assume that the 2007 image is actually showing the area with ice cover at 50% or more; but the 2008 image is showing the area with ice cover at 30% or more. In particular, the NSIDC data allows me to construct an overlay of the 50% ice, or the 30% ice, and I get a very very close match with the UIUC images when I put them all together.</p>
<p>Here are the numbers, comparing UIUC images assuming this projection, the JAXA report of 15% ice cover or more, and my own simple area-weighted sum of extent from the NASA data (f13 channel, ~25km grid)</p>
<p>For 12-Aug-2007<br />
36683 pixels of ice on the UIUC image<br />
4469014 sq km projected area<br />
4201452 sq km at 50% or more, by simple count of NASA data<br />
5057390 sq km at 30% or more, by simple count of NASA data<br />
5679174 sq km at 15% or more, by simple count of NASA data<br />
5421094 sq km at 15% or more, reported by JAXA</p>
<p>Some small differences are to be expected from processing differences; but basically the UIUC projected area lines up well with the extent of 50% ice, and JAXA lines up with the extent of 15% ice.</p>
<p>For 11-Aug-2007<br />
47822 pixels of ice on the UIUC image<br />
5882718 sq km projected area<br />
4612971 sq km at 50% or more, by simple count of NASA data<br />
5783576 sq km at 30% or more, by simple count of NASA data<br />
6462289 sq km at 15% or more, by simple count of NASA data<br />
6291563 sq km at 15% or more, reported by JAXA</p>
<p>This time the UIUC projected area lines up well with the extent of 30% ice, and JAXA still lines up with the extent of 15% ice.</p>
<p>Furthermore, I have projected the NASA data onto bitmaps, projected to align with UIUC images, and I get close agreement with the images using 50% for 2007 and 30% for 2008.</p>
<p>I&#8217;m going to stick my neck out and predict that the UIUC archived images are actually showing the extent of ice at 50% or more, and that the recent UIUC images are showing the extent of ice at 30% or more.</p>
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