NSIDC's oops moment – uncoordinated changes make for an interesting 24 hours

Many of you are probably aware of some strange goings on over at The National Snow and Ice Data Center (NSIDC) with their Arctic Sea ice graph, specifically, this one here:

You see, up until Tuesday morning, it looked like this:

If you have a keen eye, you might spot the difference, particularly in the proximity of the endpoint of the blue line to the 1979-2000 average line. How does sea ice extent go backwards you ask? Steve Goddard of real-science.com was first to spot it sent out an email notifying many people of his post titled: Breaking News : NSIDC Gets In The Data Tampering Act. I wasn’t convinced there was deliberate tampering going on, because it seemed to me to have all the marks of a processing glitch or something similar, and I made that fact known to many last night.

The two graphs (before and after on April 16th) overlaid look like this:

So not only did the extent change, going backwards, so did the climatology for computing the 2007 line and the 1979-2000 average line. This all came to light about 6PM PST Tuesday night. There was no announcement of this change on NSIDC’s website then.

While it would be easy to start pointing fingers, especially with the timing of the change (right before the extent line looked to cross the average line), I decided the best course of action would be to start asking questions before writing anything.

So I fired off emails to NSIDC’s Dr. Walt Meier and Julianne Stroeve. Strove responded first, within the hour, indicating that she could not see anything wrong, sending the image from NSIDC’s “internal network”, which is the middle graph above. That’s when I sent her the overlay (the bottom image combining the internal image she sent and the web page output image), showing that indeed there was something wrong. The light bulb went on. Walt Meier (who was traveling) responded about an hour later, with this speculation:

Hi Anthony,

Thanks for letting us know. I have a guess at what this might be.

We’re starting to make some changes to our processing to update/improve things, including some you’ve suggested. One thing that we’ve decided to do is to change the way we calculate our 5-day average values. We’ve been doing it as a centered average – i.e., a given day’s value in the plot is actually an average of that day + 2 days before and 2 days after. This caused an issue at the end point because we’d extrapolate to get a 5-day average on the last day, which resulted in wiggles at the end that.

We’re now changing it to be a trailing 5-day average, i.e., a given day’s value in the plot is the average of that day and the 4 preceding days. This will take out the wiggle in the end of the plot (or most of it – there may be some change as sometimes we don’t get complete data and need to interpolate, and later (a day or two) we do get the data and process it.

A key point is that this change doesn’t actually change the data at all; in effect it simply shifts values two days later. In other words, the centered value for Day X is the same as the trailing value for Day X+2.

This change has been implemented in our test environment and we were going to roll it out some time in near future after we tested it for a bit we planned to announce the change. I think that by accident the test code got put into production. I’d need to confirm this, but from the plot differences, this looks like what likely happened.

We’ll look into this and get back to you. I’m traveling tomorrow, but will send a note to people and I or others will get back to you as soon as we can.

walt

That seemed plausible to me, but clearly, both Meier and Strove were caught off guard, and having prominent skeptics alerting you that your most watched public output has gone haywire certainly can’t be comfortable. But, I run a bunch of servers making automated output myself, and I know how things happen. So I gave them the benefit of the doubt, particularly since they were communicating and concerned themselves.

This morning, about 14 hours after the problem was first noticed, this news item appeared on NSIDC’s web site:

Click the image for the story.

That still didn’t explain why Meier and Stroeve were blindsided with news last night from Steve Goddard and I. I queried them more, and as it turns out, they were out of the loop on the implementation. The hand and foot of NSIDC didn’t seem to have coordination on this, and it went online with no notice. Tonight, I got this email from Dr. Walt Meier that explained it:

Hi Steve, Anthony,

I think you’ve probably heard from Julienne and seen the posts we’ve made. But now that I have a chance to respond, I’ll add a few words of explanation and some thoughts. If you want to post these, you’re welcome to.

Thank you to both of you for noticing the issue and bringing it to our attention. Let me clarify (in case it’s not already clear) and provide some context. We are well aware that the daily timeseries plot, as we call it, is closely watched, particularly during the summer melt season. We’ve received various critiques of the plot, which we have taken under consideration to change when we got resources to do it. One them was the “wiggle” in the last two days of the plot. The plot was initially, and by and large still is, meant to provide a simplified glimpse of sea ice extent. The focus was on creating a clean, clear, easy to read, easy to understand graphic. As seen in other plots, the extent is often fairly noisy from day to day. Some of that variation reflects real changes, but much of it is due to limitations in the accuracy of the data or short-term weather effects, such as storm front blowing the ice one direction or another for a short period of time.

Thus, to reduce the noise and better reflect the seasonal trends we decided to use a 5-day average (5 days is a reasonable, though arbitrary, time period to reduce synoptic effects). We chose a centered average because that seemed the most logical. This means the average value is always 2 days behind the latest extent value. However, people wanted to see “today’s” value. So, we decided to provide preliminary values for those last two days by using a simple linear extrapolation. When we got enough data for a full centered 5-day average, we replaced that with the final values. However, this means that the values for the last two days change and one can get a “wiggle” in the data, particularly where there is a day or two of steep change because that day or two gets extrapolated out to 5 days. This can be misleading because, at least for a day or two, the slope may look more extreme than it really is.

I think you’re both familiar with this because it’s been commented on in the past, but I provide the background again for the full context. We refrained from changing it because of three reasons. First, after initial confusion, people understood it, so changing it could cause more confusion. Second, changing the averaging method would slightly change things in comparison with our previous analyses, namely, the date when minimum and maximum extents occur (a shift of two days). This is a minor change, but could cause some confusion. And finally, third, we wanted to make a few other changes and needed to plan resources to do them, so we put this on the list of things to do.

Last week we started to work on some changes. This was simply planning – looking at our processing, assessing what needed to be change. In the process, it was noted that changing the 5-day average would be simpler than we expected and could be done quickly. So I gave the go ahead to do this and was informed a couple days later that it had been done. However, there was some miscommunication. I was expecting that we wouldn’t put it into production immediately, but our developers assumed that it was good to go, so it went into production. Though the change had been discussed amongst all of us, the decision to do it right away happened fairly quickly and I don’t think Julienne was aware that it was in the process of being done.

In any event, what we have now implemented is a 5-day trailing average – in other words, the value plotted for a day is the average of that day and the four previous days. What this means is that there should no longer be a little. The data that we plot on a day should not change and we won’t be doing extrapolation. We think this is a better way to display the data and I think most would agree.

Another issue that wasn’t immediately noticed was that the climatology shifted more than the daily. This is because the climatology used a 9-day average. I don’t remember exactly why this was chosen, but I believe it was to make it look just a bit cleaner, though since it is an average, it already is pretty smooth. And since we were using a centered average, 5-day vs. 9-day, makes little difference. For example, the 5-day average for April 17 is 14.797 million sq km and the 9-day average is 14.801, a difference of 0.004 (4,000 sq km). Effectively, there is no difference because we estimate the precision to be on the order of 0.05 (50,000 sq km). So as long as both the daily and the climatology used a centered average, there was a consistent comparison.

However, when the centered average is moved to a trailing average there is a relative change between the 5-day daily, which slides 2 days, and the 9-day climatology, which slides 4 days. Thanks to Steve for noticing this and pointing it out. We should have it changed to a 5-day by tomorrow so that the comparison plot will again be consistent.

As for the timing of this, as mentioned above, it was mostly simply due to opportunity – we had a chance to make the change, so we decided to do it. Also, knowing that we’re heading toward the summer melt season, it was advantageous to make the change sooner rather than later. As the extent line steepens going through spring and into summer, the “wiggle” is often more noticeable. So making the change now would remove the issue for this summer’s melt season.

The fact that we made this change as the daily extent was nearing the average was entirely coincidental. It never actually entered my mind because I didn’t think it would make any difference (and it shouldn’t once we implement a 5-day average for the climatology). In fact, the change should help because we won’t be using extrapolation that can misleadingly make lines on the plot look closer than what the data really indicate.

Even using a 5-day average, short-term changes in the extent should be taken with some caution. It would be interesting if we did match or exceed the climatology, simply because it’s been several years since it happened. However, the ice near the edge now is all seasonal ice and quite thin and will melt fairly quickly. Any anomaly now will have little to no effect on the summer extent or the amount and thickness of multiyear ice.

As a final, personal note let me make a more general comment. I am saddened that some people have become so cynical about climate scientists and climate data. I can appreciate that scientists have brought some this on themselves. And of course, a healthy dose of skepticism is essential to science. But it is disappointing to see people immediately jump to conclusions and assume the worst. I hope people will take from this explanation that NSIDC, and scientists in general, are working hard to the best we can, both in understanding the science and communicating it. We’re not perfect, we make mistakes. When we find them or hear of them, we try to fix them as quickly as we can and to explain what happened as best we can. I’m proud of our team for working very hard today to address the issues, fix them, and answer questions. I think they did a great job today. And in my experience with other climate scientist, I’ve seen nothing other than that same level of dedication.

Thank you,

Walt Meier

So in a nutshell, NSIDC made a goof in implementation, and in communications. I could find all sorts of criticism for that, but I think they are probably punishing themselves far more than anything critical I might say, so I’ll just let the incident speak for itself.

I will say this though, I can’t even begin to fault them for being upfront and quickly communicative. That is a rare trait in a government agency, so on that basis, they get high marks from me, as well as my thanks. I’m fully satisfied with the explanation.

On Thursday, we’ll likely see this problem rectified, and this time I’m pretty sure I’ll get an email in advance or at the time it happens. I look forward to seeing the changes. On the plus side Dr. Meier tells me that they plan to make the raw extent data available, and that will of course allow us to plot ourselves.

=======================================

UPDATE: 4/19 9AM PST NSIDC has the new corrected graph online – see this story


		
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Marcos

now that you have their attention, can you ask why they use a 21 year avg period (1979-2000) instead of a full 30 years?

Bill Tuttle

Marcos says:
April 18, 2012 at 11:04 pm
now that you have their attention, can you ask why they use a 21 year avg period (1979-2000) instead of a full 30 years?

Simple. We didn’t have any unclassified satellite photos from the Arctic until 1979.

Robert Gee

With all regards, in these heightened days of climate awareness, the poor communication and implementation skills are very revealing. Science is supposed to be an area of exacting detail and what we continue to see is the complete opposite. Maybe Hansen could transfer in?

Peter Miller

A rare, possibly unprecedented, piece of honesty from government funded climate scientists.
Memo to Mann et alia: Here is a good role model for you.

At the same time, can you ask them why they have not moved the average period forward 10 years? Or even extended same average from 1979-2010 as noted by Marcos?

Willis Eschenbach

First, let me congratulate both Dr Walt and Anthony on this interchange, kudos to you both. That’s how it should work.
My only other comment to Dr. Walt, about his final comment:

As a final, personal note let me make a more general comment. I am saddened that some people have become so cynical about climate scientists and climate data. I can appreciate that scientists have brought some this on themselves. And of course, a healthy dose of skepticism is essential to science. But it is disappointing to see people immediately jump to conclusions and assume the worst. I hope people will take from this explanation that NSIDC, and scientists in general, are working hard to the best we can, both in understanding the science and communicating it.

Dr. Walt, people distrust climate scientists because, as climategate made perfectly clear, we were lied to and cheated by the leaders of the AGW movement, the key players in the game.
And while I am very clear that you are a good guy and an ethical scientist, and while I know you were not one of those that lied and cheated, you were indeed one of the many who said nothing after the lies were exposed. You are one of those who continues to act towards the people who did lie to us as though they had never done anything wrong. Very few climate scientists have spoken out against the outrageous scientific malfeasance and even lawbreaking by the AGW glitterati. Even fewer climate scientists have tried to get those that lied and cheated to apologize, or to pay even the slightest price for their actions. Y’all still fete them and invite them to address the conferences as though nothing untoward every happened.
So I’m sorry, Dr. Walt, but you are condemned by your silence and by your inaction to be subjected to the same opprobrium and the same mistrust as those who actually did lie, cheat, steal, subvert the IPCC, destroy evidence and encourage others to do so, pack the peer-revew boards, and try to get editors fired for publishing science that they disagreed with.
Next, we are not “cynical” about climate scientists. We are realistic about climate scientists. We got screwed by your fearless leaders, and you and most of the rest said nothing, not one damn word of protest … now you seem surprised and say you are “saddened” that we don’t trust you. Mistrust is the realistic and expected response to being lied to, it is not cynicism in any form.
One final point. For you to feel “saddened” is totally inappropriate, and it is part of the reason we still don’t trust you.
I feel saddened, and I am entitled to, because I fought hard against the loss of trust. I have done everything I could to call the culprits to account, and I have been thwarted in part by the obstinate silence of the quietly complicit … so yes, I feel sad about that.
You have no right feel saddened, you forfeited that by your silence. You should feel responsible, because you said and did nothing . The fact that you feel sad instead of feeling responsible is just one more reason why we don’t trust you.
You guys seem to think that this mistrust will go away if you ignore it … sorry. It doesn’t go away, it just gets hangs out and even gets worse, as this latest episode amply illustrates. I don’t know what you might do about it at this late date, you’ve left it awfully long to take a principled stand, but if I were in your shoes, I’d be doing something other than saying you feel sad.
w.

Marcos

Bill Tuttle says:
April 18, 2012 at 11:18 pm
Simple. We didn’t have any unclassified satellite photos from the Arctic until 1979.
Bill, i was thinking more along the lines of 1979-2009

Andrew30

The plot thickens,
the lines on the graph 🙂

DirkH

They MUST prevent arctic sea ice extent from going above the means, lest CAGW related funding is jeopardized.

Willis Eschenbach

Bill Tuttle says:
April 18, 2012 at 11:18 pm

Marcos says:
April 18, 2012 at 11:04 pm

now that you have their attention, can you ask why they use a 21 year avg period (1979-2000) instead of a full 30 years?

Simple. We didn’t have any unclassified satellite photos from the Arctic until 1979.

Since that’s more than thirty years, I’m not sure why that’s relevant. They could use the thirty year period 1979-2010 …
w.

Richard111

“On the plus side Dr. Meier tells me that they plan to make the raw extent data available, and that will of course allow us to plot ourselves.”
Very well done indeed. If only the temperature wallahs did the same we would live in a calmer world. (kama? 🙂 )

Bill Tuttle says:
April 18, 2012 at 11:18 pm
Simple. We didn’t have any unclassified satellite photos from the Arctic until 1979.

You do realize that you didn’t even come close to answering the question. Both UAH and RSS temperature series now use 20 30 year averages and they both start in 1979/80. What you failed to grasp is that there is now should be 30 years of available satellite data for them to use 1981-2010.

I have been wondering why both the NANSEN Artic ROOS sea ice graphs has been frozen since April 5th.
http://wattsupwiththat.com/reference-pages/sea-ice-page/

boballab says:
Your comment is awaiting moderation.
April 18, 2012 at 11:36 pm
Both UAH and RSS temperature series now use 20 year averages

Gah this what I get for staying up late. The above should be Both UAH and RSS temperature series now use 30 year averages.
[Fixed. -w.]

I still dont understand. My problem with this issue was not the moving 5 day average, but the historical mean. Can someone explain why the historical mean shifted?
:-/…

LearDog

Walt Meier is PRECISELY the kind of guy we need in generating these important data. I agree with him – it is sad to see scientists tarred and feathered because of the actions of several vociferous, nortorious few.
It shows the importance of clean and transparent data. Hats off to him…

AlexS

The minimum acceptable they should do is show the 2 graphics for at least 30 years.

Why use any gray zone at all? Plot the data, all of it. Not difficult. Or the actual data range. Again not difficult.
The “2 standard deviations” is an artifact of some damn T-test. I hate that crap. Why not 2.1 “standard deviations? Or 1.9? The statistical theory behind it is not applicable in this case. What happened is what happened and I would rather see the actual data than some artificial 95% confidence limit on a known set. Map the data not some aberrant tweak of it, you know?
BTW, the “average” is a mythical creature. Not real. Just a smoother. Never happened like that.

NZ Willy

Yay, thanks Anthony, that does explain the change in the Antarctic graph as well, even tho not mentioned. They do other adjustments that I’ve seen mentioned before, like for reflectivity of water-on-ice during the melt season, etc, and that would also cause offsetting conditions between Arctic and Antarctic, if treated (anti) symmetrically. However, note the 5-day average used. This wouldn’t be needed if each day’s measurement was robust. There is obviously a lot of noise compared with the signal. A few assumptions can help to minimize that noise, and somewhere in that code, I’ll bet, some are built in. Worth watching onwards. Trust, but verify.

HLx: Very good point. What caused the line representing the period from 1979 through 2000 to change? There never was a problem with wiggles at its end point (it has no end point) and changing from a 5 day moving average to a 9 day moving average when plotting 2012 temperatures has little to do with data that’s already over 12 years old.

Max

If they showed the average trend 1979-2010 …I imagine everything would appear in the shaded area. Not so alarmist then.

MattB

Some discussion about why they don’t post a 30 year average not the 1979-2000 average . My opinion is that they are deliberately wanting to compare “today” with what the average was between 1979-2000, so you can see the difference. That is, the graph is set up to compare any given year with how it “used to be”.

Richard S Courtney

Anthony:
You wrote;
“So in a nutshell, NSIDC made a goof in implementation, and in communications. I could find all sorts of criticism for that, but I think they are probably punishing themselves far more than anything critical I might say, so I’ll just let the incident speak for itself.
I will say this though, I can’t even begin to fault them for being upfront and quickly communicative. That is a rare trait in a government agency, so on that basis, they get high marks from me, as well as my thanks. I’m fully satisfied with the explanation.”
AMEN!
We need to commend the good as well as exposing the bad. Sadly, there has been – and is – so much which is bad in climate science that it is easy tio overlook the good.
Error correction is a part of sustaining standards and we need to congratulate people when they take prompt action to check, admit, explain and erradicate mistakes as NSIDC has done in this case.
NSIDC, good job, well done!
Richard

Willis Eschenbach

Dr Walt, upon re-reading my post above I realize that you have been the unlucky recipient of my frustration with climate scientists not cleaning up their own back yard.
I want to emphasize that I think you are an honest scientist. In addition, you have been one of the few mainstream climate scientists willing to expose your ideas to the harsh uncensored light of the web, whether here or elsewhere. You are not one of those whose climategate correspondence convicted them in their own words of lies and behind-the-scenes machinations, your name is nowhere mentioned. You have been clear and responsive about difficulties with the information you provide, including this latest case. My honest opinion is that you are a good man.
Unfortunately, as they say, for corruption to triumph, it only requires that good men do nothing …
w.

So Dr. Walt Meier is either a really nice, honest chap or just writes (or has written for him) a more intelligent letter. AGW player possibly good at chess shocker.

So it was all just a coincidence. Nothing political or ideological happening at all.

Its only by people like watts up with that that climate advocates will be prevented from telling a whole pack of lies. Well done.

Caleb

“But it is disappointing to see people immediately jump to conclusions and assume the worst.”
When I see the name “Walt Meier” I don’t assume the worst. He has earned respect.
However the same cannot be said of others, nor of the government in general. Therefore anything which does not pass the smell-test draws immediate scrutiny. After all, there are ways to get around an honest man, and honest men can even be replaced.
Speaking of drawing scrutiny, there is something funny going on at the NOAA “ENSO Cycle” site, at http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-
fcsts-web.pdf
Pages 27 and 28 hold two models of what the ENSO is predicted to do, the old CFS model (which soon will be discontinued,) and the new CFSV2 model.
On the left hand side of both pages are a series of maps which show how the sea temperatures are suppose to evolve. In the typical manner above normal is red, and below normal is blue. Near normal is white.
What I find odd is that the old CFS model has a fair amount of white on its maps. The CFSV2 maps are very scarlet.
In honor of Walt, I will try not to jump to any conclusions. However I will point the change out, so people more skilled at sifting data than I am can focus on why the maps so abruptly get so much redder. (The scale seems to be the same.)

Darkinbad the Brightdayler

Willis, you can’t have your cake and eat it too.
He quickly fessed up to his own mini snafu and dealt with it like a true scientist.
Getting seriously involved in the whole climategate thing involves taking a lot of time out to study what the various protaganists actually said and ditto for checking their sources.
Its easy to stand in the bleachers and shout with the crowd but a lot harder to deliver a serious performance on the field.
That is, if you see the whole thing as a very black and white us and them scenario.
If you see it as a whole spectrum of opinions and a hotchpotch of half baked grand theories and a tartan weave of interlacing ideas then it makes a lot less sense to be throwing your weight about.
If Walt were my employee, I’d be expecting him to devote the bulk of his time to my business, concentrate on getting his science right and only speaking out where he saw things awry in his area of expertise.

Ally E.

Beautifully said, Willis.

Richard S Courtney

MattB:
re your post at April 19, 2012 at 12:21 am, nobody knows “how it used to be”.
The graph shows how ice cover has been varied in the recent few decades since satelite data has been obtained.
We have historical data which indicates times of less ice than in those recent decades, but that data cannot be posted on the graph.
So, your “opinion” is wrong.
Richard

Caleb
paullm

Damn, Willis, don’t be so restrained! I concur, silence from an authority figure who knows/suspects the given line is false/compromising reinforces a falsehood and/or reduces other perspectives – guilty. However, perceived self-preservation and comfort will always affect a significant percentage of us. The process must remain a major rule. The rule of process, not the rule of self/consensus.must rein. Ha, the never ending challenge.

richard verney

Anthomy
Glad to see that you are now running with this one, which I first saw on Steve Goddard’s site, but he does not have the following/volume you have. So very useful that it is on your site..
Congratulations on how you have handled matters. Very good to see that you got involved and the exchanges are interesting.

beesaman

I love it how Arctic ice prior to 1979 is assumed somehow to be thicker and greater in extent. We have very little accurate evidence either way for that and the further we go back the less evidence we have. What I have observed is that the outer regions of Arctic ice fluctuate massively and much of that depends upon local weather events rather than global climate shifts and that the core Arctic ice can be likewise influenced. However, there does seem to have been some warming since the late seventies and a reduction in that core Arctic ice, but that may well be reaching a reversal point. It will be interesting to watch over the next few years, especially as any recovery would be a real death blow to AGW and boy do the main protagonists know it, hence the healthy skepticism concerning any changes to such data. After all you can fudge some of the data some of the time but you can’t fudge all of the data all of the time!

Scottish Sceptic

It would appear that this is an innocent change – although the timing is highly questionable.
The evidence is that it was implemented in a hurry without proper consultation just before the graph turned in the sceptic favour.
Cherry picking …. picking valid data that just happens to support a point of view.
Upjusting … the selection of data which in themselves are apparently innocent choices but which consistently create a bias in the data by cherry picking analytical tools that support a point of view.

Ally E.

I would really like to see the average of this graph extended. I don’t like the 2000 cut off. Too many graphs are chopping out the cooling from ’98 onward. When is that going to change? We’re already into 2012. They can’t keep dragging it out. It’s going to look bloody stupid if we’re still looking at a graph cut off at 2000 when we’re at 2015 or 2020 or 2050. It looks bad enough now.
And I still agree with Willis. He has the point exactly right. Climategate should have raised the hackles of every scientist. Silence is not the answer and never will be. If it weren’t for the few speaking out, we’d be knee-deep in socialism right now.

Whatever way the data is presented, there is clearly something odd going on with Arctic ice. I find it strange that everyone seems much more interested in the NSIDC than the icecap itself. In a short space of time, the ice cover has gone from below the 2007 level to close to the 1979-2000 average. What seems to be happening is that the ice is melting much slower than in previous years.
Does anyone have any comments on or possible explanations for this phenomenon ?

Greg Holmes

Thanks Antony, perhaps there are a few scientists out there involved in climate research who still have a moral/ethical code and live up to it. Hat tip to them.

Jeef

I still don’t get why the average (black) line has been amended. Is that to do with the 5 vs 9 day too? Well done Walt and team for being so responsive, by the way.

orson2

Excellent work, Anthony. Even such small chores as getting data transparency is a big deal. And finding scientists open and communicative is a win-win for everyone. Thanks.

Jeef

Last thought – is it just me or the period in the linked article that makes track lower on the upslope and higher on the down?

Lars P.

Thanks for the explanation and the follow-up. . A plus point to Steven for the careful tracking!
I can understand the feeling as expressed by Walt Meier, but trust it is important also for the keepers of the data to understand that they got the attention of the skeptic community and all the adjustments are closely watched.
There are many reasons why skeptics track now very closely all these graphs as these have been often misused and adjusted to support somebodies view or theory:
http://suyts.wordpress.com/2012/04/11/this-isnt-about-the-climate/
Very difficult to understand at a later time what had happened at the time of adjustment if there is no clarity. For instance at the sea level tracking, there was a 7 mm adjusting up of the sea level in 2007. The adjusting was not added as difference between 2006-2007 but for the whole period 1993-2007.
The adjustment are evident if one tracks back the previous year values. A german skeptic group used the way back archive for this:
http://hockeyschtick.blogspot.com/2012/04/analysis-finds-satellite-data-has-been.html
It is evident also in checking the UC data as communicated in each year which shows values at or under 1mm for the years since 2005, but the total graph shows 3mm+ for these years.
http://suyts.wordpress.com/2012/04/10/sea-level-rises-to-new-lows/

Bill Tuttle

boballab says:
April 18, 2012 at 11:36 pm
You do realize that you didn’t even come close to answering the question. Both UAH and RSS temperature series now use 20 30 year averages and they both start in 1979/80.

I answered the 1979 part correctly, so can I get a partial credit?

ZZZ

You take an average, 5 day or 9 day or whatever, and then you have a problem: what date — that is, x axis value — do you assign to this time average. The honest date is one in the center. Assigning a date that corresponds to the most recent day in the average makes no sense unless you want to confuse the issue. Why not just live with a 2-day delay for the average value? People who want the very latest values can look at the raw, unaveraged data.
Assigning a time value to a trailing average that corresponds to the time of the last value used in the trailing average is, by the way, done all the time in time-averaged stock market graphs. There the stock analysts want to compare the latest stock price to the time-average to see whether it has gone above or below that time averaged value that should properly be set back in the past (how far in the past depends, of course, on how much time has been averaged over). Hence they push the graph of the time average forward so it directly creates this comparison — and they do it by assigning a time to the time average that corresponds to the latest stock value put into the average. This is, of course, exactly what the ice-coverage people have done here. As a quick way of comparing stock prices this procedure may make some sense, but when talking about physical processes it does not. They should go back to the old way of plotting their time-average data and not try to extrapolate in order to guess what the last several data points will be. So what if the rest of us have to wait for those last few average values until they actually exist!

Kasuha

I don’t wonder they decided to change the method if they were getting accused of manipulating the data (clearly mostly from ‘skeptic’ side) as the end of the graph wiggled with more data being added. This new way is rock solid, any added point will just stay in place and I think it’s no problem that what they reall did was that they just cut off the last two days of the old graph.
And that they did not fit individual parts of the graph correctly on the first attempt – things like that happen, we’re only humans. It’s good to see they handled it in a professional way.

Kolenaty

Anthony,
Is there anything that would make it unseemingly for you to provide a version of the Sea Ice graph that contained an estimate for the missing years’ data? Just doing so for a single month would give us some notion of how much (or how little) is being introduced in using the shortened series.

Sera

Willis- that seems a little harsh to lump Walt into that catagory. I don’t ever remember him being arrested, or acting like a fool or not responding FULLY to even the slightest criticism. I’ll be the first to jump headlong into the fray, but I’ll give quarter to Dr. Meier.

Galane

Why didn’t they just change to a two or three day trailing average for the end of the graph while leaving the rest of it at the centered 5 day average? Couldn’t be that much harder to implement in the plotting software. Add a conditional check to the averaging code for when it gets to the latest date in the data.
With that, the graph wouldn’t have shifted and the “wiggle” at the end as the plot advanced would go away. The vast majority of people watching that would never have noticed any change.

Otter

To Walt Meier, and I hope you are reading here: You answered swiftly. You gave a great deal of info, allowing people to work things out and see where you were going. You were polite.
I’m sure there’s a lot more you did there (but my time is limited). So: We could use more people like you, and a great deal LESS people like mann, billy Connolley, et al.