By Steven Goddard
[see important addendum added to end of article ~ ctm]
[Note: The title and conclusion are wrong due to bias in the start/end point of the graph, the mistake was noted by Steven immediately after publication, and listed below as an addendum. I had never seen the article until after the correction was applied due to time difference in AU. My apologies to readers. I’ll leave it up (note altered title) as an example of what not to do when graphing trends, to illustrate that trends are very often slaves to endpoints. – Anthony]
JAXA Arctic Ice measurement just had its 8th birthday. They have been measuring Arctic ice extent since late June, 2002.
http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm
We normally see year over year ice graphs displayed in the format above, with each year overlaid on top of previous years. The graph below just shows the standard representation of a time series, with the linest() trend.
As you can see, Arctic ice extent has been increasing by nearly 50,000 km² per year. Over the eight year record, that is an increase in average ice extent of about the size of California. More proof that the Arctic is melting down – as we are constantly reminded. Spreadsheet is here.
How do we explain this? There has been more ice during winter, paralleling the record winter snow in the Northern Hemisphere. Meanwhile in the Southern Hemisphere, ice extent is at a record high for the date.
Size matters, but I’m guessing that Nobel Prize winner Al Gore didn’t share this information with his masseuse.
Addendum:
I realized after publication that this analysis is biased by the time of year which the eighth anniversary occurred. While the linest() calculation uses eight complete cycles, it would produce different slopes depending on the date of the anniversary. For instance, had the anniversary occurred in March, the trend line would be less steep and perhaps negative.
This is always a problem with graphing any cyclical trend, but the short length of the record (8 years) makes it more problematic than what would be seen in a 30 year record.
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The JAXA dataset starts with a trough and ends with a crest, should anyone be surprised if the trend is upward, given these boundary conditions.
Any one schooled in analysis of cyclical data would know that one must go from crest-to-crest or trough-to-trough, to maintain some semblance of symmetry about the x-axis.
Presenting an asymmetric derived trend line, known a priori to rise or fall, depending on whether one starts with a trough and ends in a crest or starts with a crest and ends with a trough, earns you an F- in data analysis.
The title of this post is misleading, incorrect, and 100% wrong.
Too quick to print on this one, basic mistake, instant critique, instant correction, left on blog for all to see.
That gives me confidence in reading this blog.
If only the warmist science/media machine worked that way, eh?
Given that this post is admittedly wrong it should be promptly retracted and let professionals do the job.
your result was not “biased by the time of year”. it was plain out false.
why not add a simple “i was completely wrong” to the headline?
Please forgive me if I stray from the topic, but just to give you a reminder of the forces of the irrational at work over there (if not here in UK); this taken from comments from something in that gem of journalistic excellence, the Huff. Po., on the BP spill and the possible US climate bill (ID of poster to remain anon.):
“…Ironically, moving beyond oil and other fossil fuels appears possible much more rapidly than is generally believed.
A very thin film of oil on the surface in the North Atlantic and Arctic oceans apparently could raise temperatures toward a catastrophic Tipping Point.
The White House must rapidly consider the possibility that a massive mobilization is needed to combat what might be looming if…”
etc., etc.
The bit about the ‘tipping point’ should be good for a few laughs (with 635k giving up employment hopes in June in the US, these are needed). Also, thanks for the nice website (maybe you and the others will save perhaps part of the remainder of US manufacturing capacity by helping to put the spanner in the works of cap-and-trade).
Michale Cejnar says:
July 2, 2010 at 3:14 pm
Too quick to print on this one, basic mistake, instant critique, instant correction, left on blog for all to see.
That gives me confidence in reading this blog.
If only the warmist science/media machine worked that way, eh?
___________________________________________________________
It’s wrong, he knows it’s wrong, yet no retraction of this extremely biased analysis, and no change to the post titled;
“Arctic Ice INCREASING By 50,000 km2 Per Year (if you start with a trough and end with a grest, oops, my bad, I don’t know what I’m doing)”
How many sharpshooters read and understood the addendum?
“While the linest() calculation uses eight complete cycles, it would produce different slopes depending on the date of the anniversary.”
The only reason not to retract this is in the hopes that the headline is picked up and passed around as misinformation.
I’d like to think you are better than that.
I rather thought that the location of the endpoints to “show a trend” was the whole point of the post.
Sauce for the goose…
Is there a commonly available version of the sea ice extent graph incorporating both artic and antarctic together.
CAGW-Skeptic99 says:
July 2, 2010 at 3:33 pm
How many sharpshooters read and understood the addendum?
“While the linest() calculation uses eight complete cycles, it would produce different slopes depending on the date of the anniversary.”
___________________________________________________________
Did the addendum come before or after the commentary started (Ian H)?
If it occured before, then the author knew a priori, that the analysis was highly suspect, but posted in anyway with the misleading headline.
If it occured after, then the misleading headline needs to be changed, or this biased article needs to be retracted in it’s entirety from WUWT.
“Hide the decline.”
Indeed.
FrankS
This is what you are looking for.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg
EFS_Junior
Read the top of the article now, and compare notes vs. the hockey stick decade long (and ongoing) stonewall.
WUWT corrects within an hour of publication.
Per Ian H’s comments, when I calculated the simple linear regression using the 2003 and 2009 maxima for the start and end points, I get a trend of -20900km^2/year. Using the 2002 and 2010 minima for the start and end points I get -72700km^2/yr.
What this tells me is that a simple linear regression on a sinusoidal data series is not a valid expression for the trends. It is far to dependant on the start and end points to be of any real value.
This article was published and peer reviewed within two hours. Wouldn’t it be great to see all climate science treated in the same manner whatever its source?
tonyb
The biggest problem with the Sea Ice Extent Discussion, is that 8 years of data is TOO
SMALL of a sample, to allow ANY conclusions to be determined.
You boobed, admitted your error and apologised. You’re clearly not following the route-map for climatological approved behaviour.
Thank you Steve, your honesty may buck against the trend for PNS, be irrelevant to the critical faculties of lick-spittling whitewashers but, nonetheless, is very much appreciated!
I applaud you for retracting so quickly. People would have had a lot of fun at your expense, if you hadn’t.
Happy 4th of July, to all the Americans.
Happy weekend, to everybody else. Or, you can celebrate with us, too.
Sod,
How about the Southern Hemisphere sea ice extent? Any comments? Is it so desperate?
My bad. I goofed when I did the chart for the min-min. That should have been -114300km^2/yr.
While the analysis error is bad, I like the idea of keeping the post as an example of open debate, when to fess up on a mistake, etc.
The thing that really gets me is how so many people are up in arms about this, demanding a retraction, etc on the very day it was posted…yet they stay quiet on or even claim validity of the hockey stick icon which was shown to be wrong years ago and which had/has a much larger impact.
-Scott
I’ll say it again, EVERYBODY SLOW DOWN.
Speed won’t win this “war”, facts will.
The dogma is so ingrained, it will take patience, and time.
A change is coming in November, but will things change ??
Everybody makes mistakes.
Far fewer own up to it immediately.
Experience is a great teacher.
I plotted the JAXA data, and inserted a trend line. I used a start date of June 21 2002, and an end date of June 21 2010.
I get a positive trend of 142.58 sq km per day, or 52,077 sq km per year.
Of course, R2 is very low, at .0016.
Using a start and end date of Sep 10 (approx ice minimum) we get a trend of -241 km/day or nearly 88,000 sq km/year.
Using a start and end date of Mar 25 (approx ice max), we get about -35 sq km per day, or about 12,700 sq per year.
As stated, the start/end date changes the slope.
It might be interesting to plot the slope, as a function of month, or even, day of the year.
tonyb says:
July 2, 2010 at 3:58 pm
This article was published and peer reviewed within two hours. Wouldn’t it be great to see all climate science treated in the same manner whatever its source?
Tony, you’re spot on once again!
This is the way that we need to peer-review from now on. Not gatekeeping, nor appeals to authority via a self-seeking, peer-review process that claims that only its accredited disciples are competent to judge!
Steves mental processing was laid bare, was replicable and found to be faulty. The self-styled Science of Climate, has been characterised via its most enthusiastic adherents by non-transparency, obfuscation and smellingfications of deceipt. The deceipt is still denied!