NSIDC: satellite sea ice sensor has "catastrophic failure" – data faulty for the last 45 or more days

http://gbailey.staff.shef.ac.uk/researchoverview_images/dmsp.jpg

The DMSP satellite is still operating, but the  SSM/I sensor is not

Regular readers will recall that on Feb 16th I blogged about this graph of arctic sea ice posted on the National Snow and Ice Data Center sea ice news page. The downward jump in the blue line was abrupt and puzzling.

nsidc_extent_timeseries_021509

Click for larger image

Today NSIDC announced they had discovered the reason why. The sensor on the  Defense Meteorological Satellite Program (DMSP) satellite they use had degraded and now apparently failed to the point of being unusable. Compounding the bad news they discovered it had been in slow decline for almost two months, which caused a bias in the arctic sea ice data that underestimated the total sea ice by 500,000 square kilometers. This will likely affect the January NSIDC sea ice totals.

Map of sea ice from space, showing sea ice, continents, ocean

Figure 1. High-resolution image Daily Arctic sea ice extent map for February 15, 2009, showed areas of open water which should have appeared as sea ice. Sea Ice Index data. About the data. Please note that our daily sea ice images, derived from microwave measurements, may show spurious pixels in areas where sea ice may not be present. These artifacts are generally caused by coastline effects, or less commonly by severe weather. Scientists use masks to minimize the number of “noise” pixels, based on long-term extent patterns. Noise is largely eliminated in the process of generating monthly averages, our standard measurement for analyzing interannual trends. Data derived from Sea Ice Index data set.

—Credit: National Snow and Ice Data Center
Graph with months on x axis and extent on y axis

Figure 2. High-resolution image

Daily total Arctic sea ice extent between 1 December 2008 and 12 February 2009 for Special Sensor Microwave/Imager SSM/I compared to the similar NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor. —Credit: National Snow and Ice Data Center

Dr. Walt Meier of NSIDC had planned to do a guest post here on WUWT, but this evening, with the magnitude of the problem looming, he’s asked to defer that post until later. I certainly can’t fault him for that. He’s got his hands full. Hopefully they have a contingency plan in place for loss of the sensor/space platform. I applaud NSIDC for recognizing the problem and posting a complete and detailed summary today. I’ve resposted it below in its entirety. Note that this won’t affect other ice monitoring programs that use the  Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, which is on an entirely different platform, the AQUA satellite.

UPDATE: 2/19 Walt Meier writes with a clarification: “One detail, though perhaps an important [one]. I realize that it is bit confusing, but it is just one channel of the sensor that has issues. And it isn’t so much that it “failed”, but that  quality degraded to the point the sea ice algorithm – the process to convert the raw data into sea ice concentration/extent – failed on Monday.” – Anthony

From NSIDC Sea Ice News:

As some of our readers have already noticed, there was a significant problem with the daily sea ice data images on February 16. The problem arose from a malfunction of the satellite sensor we use for our daily sea ice products. Upon further investigation, we discovered that starting around early January, an error known as sensor drift caused a slowly growing underestimation of Arctic sea ice extent. The underestimation reached approximately 500,000 square kilometers (193,000 square miles) by mid-February. Sensor drift, although infrequent, does occasionally occur and it is one of the things that we account for during quality control measures prior to archiving the data. See below for more details.

We have removed the most recent data and are investigating alternative data sources that will provide correct results. It is not clear when we will have data back online, but we are working to resolve the issue as quickly as possible.

Where does NSIDC get its data?

NSIDC gets sea ice information by applying algorithms to data from a series of Special Sensor Microwave/Imager (SSM/I) sensors on Defense Meteorological Satellite Program (DMSP) satellites. These satellites are operated by the U.S. Department of Defense. Their primary mission is support of U.S. military operations; the data weren’t originally intended for general science use.

The daily updates in Arctic Sea Ice News & Analysis rely on rapid acquisition and processing of the SSM/I data. Because the acquisition and processing are done in near-real time, we publish the daily data essentially as is. The data are then archived and later subjected to very strict quality control. We perform quality control measures in coordination with scientists at the NASA Goddard Space Flight Center, which can take up to a year. High-quality archives from SSM/I, combined with data from the earlier Scanning Multi-channel Microwave Radiometer (SMMR) data stream (1979–1987) provide a consistent record of sea ice conditions now spanning 30 years.

Data error sources

As discussed above, near-real-time products do not undergo the same level of quality control as the final archived products, which are used in scientific research published in peer-reviewed journals. However, the SSM/I sensors have proven themselves to be generally quite stable. Thus, it is reasonable to use the near-real-time products for displaying evolving ice conditions, with the caveat that errors may nevertheless occur. Sometimes errors are dramatic and obvious. Other errors, such as the recent sensor drift, may be subtler and not immediately apparent.  We caution users of the near-real-time products that any conclusions from such data must be preliminary. We believe that the potential problems are outweighed by the scientific value of providing timely assessments of current Arctic sea ice conditions, as long as they are presented with appropriate caveats, which we try to do.

For several years, we used the SSM/I sensor on the DMSP F13 satellite. Last year, F13 started showing large amounts of missing data. The sensor was almost 13 years old, and no longer provided complete daily data to allow us to track total daily sea ice extent. As a result, we switched to the DMSP F15 sensor for our near-real-time analysis. For more information on the switch, see  “Note on satellite update and intercalibration,” in our June 3, 2008 post.

On February 16, 2009, as emails came in from puzzled  readers, it became clear that there was a significant problem—sea-ice-covered regions were showing up as open ocean. The problem stemmed from a failure of the sea ice algorithm caused by degradation of one of the DMSP F15 sensor channels. Upon further investigation, we found that data quality had begun to degrade over the month preceding the catastrophic failure. As a result, our processes underestimated total sea ice extent for the affected period. Based on comparisons with sea ice extent derived from the NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, this underestimation grew from a negligible amount in early January to about 500,000 square kilometers (193,000 square miles) by mid-February (Figure 2). While dramatic, the underestimated values were not outside of expected variability until Monday, February 16. Although we believe that data prior to early January are reliable, we will conduct a full quality check in the coming days.

Sensor drift is a perfect but unfortunate example of the problems encountered in near-real-time analysis. We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice, which is based on the the consistent, quality-controlled data archive discussed above.

We are actively investigating how to address the problem. Since we are not receiving good DMSP SSM/I data at the present time, we have temporarily discontinued daily updates. We will restart the data stream as soon as possible.

Some people might ask why we don’t simply switch to the EOS AMSR-E sensor. AMSR-E is a newer and more accurate passive microwave sensor. However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years. There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods. Our main scientific focus is on the long-term changes in Arctic sea ice. With that in mind, we have chosen to continue using the SSM/I sensor, which provides the longest record of Arctic sea ice extent.

For more information on the NSIDC sea ice data, see the following resources on the NSIDC Web site:

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John Egan

Will NSIDC issue a correction to the media?
“Arctic sea ice coverage was at its sixth lowest January extent since satellite records began in 1979, according to the National Snow and Ice Data Center. Average ice extent during January was 5.43 million square miles.”
This was released in a number of news outlets –
http://www.examiner.com/x-219-Denver-Weather-Examiner~y2009m2d18-January-was-seventh-warmest-for-globe
And was also part of the larger NOAA January report –
http://www.noaanews.noaa.gov/stories2009/20090218_globalstats.html

Satellite Lover

Its sad to see F13 degrade. Having personally helped build the SSM/I sensors its a bit like having family get sick. We can take solace in the fact that the original mission life was just 3 years and it worked for over 4 times its design life. Hopefully there are still other sensors available to replace the missing data.

RonPE

Bravo Anthony! Your original statement “Something odd is going on . .” has suddenly become “Houston, we have a problem.”

Ray

It’s not that I like to repeat myself but I did question the december flatness (and slight drop) several times already. In view of this important piece of information, will they review, as a minimum, the past 6 months data?
REPLY: I’m sure they’ll go over everything, because much of the data is now in question. – Anthony

F Rasmin

I noticed that some Canadian cities have disappeared off the national temperature map on the right. As an Australian, I had always thought that there were friendly relations between the US and Canada.
REPLY: If the data isn’t reported from the station, the plot is not made- Anthony

Leon Brozyna

To say that Dr. Meier has his hands full is an understatement. I still wonder why it took so long for anyone to question the gradual appearance of oddities in the visual representation of ice extent until this late date, e.g. the growing number of gray areas.
What I am wondering about now, from that last paragraph in today’s explanation, is why, if AMSR-E data is so much more accurate, it can’t be used. Why can’t the newer data from AMSR-E be spliced onto the previous data? I hope that in a future post he can go into more detail about this.
I do notice that their representation of current AMSR-E data shows ice extent near 15 million km². I assume that JAXA also uses this data; however, their latest early number for 18 Feb puts ice extent at 14.185 million km², so I guess they’re filtering the data with their own algorithm.

Phillip Bratby

So although they have consistent data far 30 years, they are now recognising that the data provide “less accuracy”. The question is how accurate are that 30 years of data. Can the statement “the scientific conclusions about the long-term decline of Arctic sea ice” be relied on, since they are based on less accurate data?

Clive

Anthony,
Thank you for this revelation.
In mid December, I noticed that sea ice growth had flatlined and thought that strange since it had been very cold in N Canada and N Russia. I wrote to NSIDC on December 21 and received the reply below from David Korn at NSIDC. I still am not sure why the sea ice would not have grown when there was no sunlight and it was darned cold. That is obviously highly subjective on my part … but still.
If the mid December levels are indeed accurate (they may well be) then growth rates have little to do with air temperatures but can only be wind and or ocean currents.
The scientist was careful NOT to blame “climate” and said it was a short-term “weather” occurrence.
I remain highly skeptical about sea ice measurements. Your revelation is most interesting. Makes one wonder a lot.
Clive Schaupmeyer
Alberta
REPLY FROM NSIDC Dec 22, 2008.
Thank you for contacting NSIDC. I forwarded your question to one of our
sea ice experts and here is his response:
“NSIDC scientists are quite certain that the almost complete lack of increase in ice extent since about December 10 is real. Satellite-derived ice extent from the SSM/I (Special Sensor Microwaver/Imager) used to create the time series on our website was checked against extent based on the AMSR (Advanced Microwave Sounding Radiometer) instrument. AMSR shows the same pattern. This gives us independent confirmation. Past 10 days has seen a very unusual atmospheric pattern. It has been very warm over the Arctic Ocean, and wind patterns have favored a compact ice cover. While the lack of increase in ice extent is certainly quite unusual, we would not read too much into it right now at it appears to be weather related versus climate related. It will be interesting to see what happens over the next week.”

It is good to see an error acknowledged and steps taken to correct it.
John Egan’s comment is important and I hope that the correction is issued when available. My own sense is that the sea ice people are not “on the team” but rather trying to bring real data to the discussion. That’s vital and so is error correction.
We need good data and, thankfully, when errors occur there is at least one group of scientists who are willing to deal with the errors.

VG

This is why I WOULD believe data from NSIDC in the future, whereas before I had my doubts. This is a most enlightening phenomenom. So does the extra 500,000 put the line back up “normal” maybe someone can re-do the graph to what it should/would look like corrected. BTW if it does really melt again I would trust NSIDC to truly report the results and corrections ect..

Ben

[snip – none of that. See first comment]

VG

Re Previous it is however a bit of a worry that cryosphere today puts this on top of their web page (see below in parenthesis) It shows a bias towards any mention that ice may be close to normal especially in light of recent NSIDC problems. This is one site which I would have trouble with just becaue of this. They should just put the data up and not put comments like this. It actually does a disservice to their “global warming” cause.. but on the light side, being a skeptic I applaud it! LOL
“February 15, 2009
In an opinion piece by George Will published on February 15, 2009 in the Washington Post, George Will states “According to the University of Illinois’ Arctic Climate Research Center, global sea ice levels now equal those of 1979.”
We do not know where George Will is getting his information, but our data shows that on February 15, 1979, global sea ice area was 16.79 million sq. km and on February 15, 2009, global sea ice area was 15.45 million sq. km. Therefore, global sea ice levels are 1.34 million sq. km less in February 2009 than in February 1979. This decrease in sea ice area is roughly equal to the area of Texas, California, and Oklahoma combined.
It is disturbing that the Washington Post would publish such information without first checking the facts.

Clive

RE: My post above and the reply from NSIDC
The reply said, “It has been very warm over the Arctic Ocean”
I know oceans are way different than land, but the mean temp for December at Alert was -37°C and the December mean was -42°C at Eureka. I checked one inland base in Siberia (Dzalinda) and the temps around mid December were -40 and -50°C. Land is not ocean. Fine. But golly why would it be “very warm over the Arctic Ocean” in that same period when the surrounding arctic lands were bloody cold? I don’t get it.
Maybe “very warm” is -30°C ☺ I am most skeptical about sea ice data.
Thanks Anthony. Good stuff. Best wishes,
Clive Schaupmeyer
Alberta

Tim L

well, it took two days but they have come clean.
really this is no problem but with the hipe of co2 etc. it becomes a big deal,
I am glad not to be in there shoes as to get things back on line.

Pragmatic

VG (23:03:42) :
“This is why I WOULD believe data from NSIDC in the future, whereas before I had my doubts.”
In the future, just as in the past, errors in data processing and hardware systems will inevitably occur. Which reminds that no measurement technology is infallible, nor should it be considered unreliable. For greater accuracy, considering the weight given to sea ice by MSM and policy makers, field measurements could be of great value. As noted in recent sea level measurements, in-situ data sets often conflict with satellite measurements. And in the past, NOAA satellites have had significant calibration problems yielding entire records unusable.
Again, thanks to the NSIDC staff for addressing this issue openly. And to their volunteers who, apparently are charged with maintaining the website but are not compensated for their time.

AndyW

Congrats to Sven in the last thread about this, in spotting the trend was higher than normal compared to 2 other graphs since the start of the year.
I personally only look at the JAXA graph but it pays to look at multiple I guess to be able to pick up on anomalies of this sort.
I wonder if Anthony’s original blog entry and comments later made them look more closely to help them spot the failing sensor problem more quickly or whether it was already being investigated? If the former then I retract my statement that this was not worth commenting on, it certainly was!
Regards
Andy

Dr Meier, if you’re watching, I’d like to add no personal criticism at all. How could I? You have done nothing wrong.
But I would like to make a point: in the world of the Internet and especially in the field of climate science, an anomaly in a reading from a satellite is news and it is worth investigating even if the anomaly turns out to be nothing.
In this case, it pointed to something rather severe.
I don’t ask for an apology (nor I think, would Anthony). But I would like an acknowledgement that Anthony was correct to bring this to everybody’s attention. It is in no-one’s interest to have bad or doubtful data in the record, I’ll think you’ll agree.

Flanagan

Argh, that’s a blow for me – I just loved to check their plots from time to time to see how ol’ good arctic was doing…
I guess we “only” have JAXA, ROOS and cryosphere now. It’s always better to have multiple sources to guess trends…
Concerning the CT post, I totally agree with them of course. They should not tolerate that a journalist uses fake numbers and cites them as a source, whatever the bias. It’s a question of reputation.

anna v

I also want to add my voice in thanking Dr. Meier for the oneness of this discourse.
Errors have happened, will happen again. It is the sign of a true scientific discipline that errors are acknowledged openly, and corrected. Let us hope that other data providers are as open as this.
It is not surprising that the error was not caught before it became large. When most of the publicly funded climatologists and technicians on all levels are biased towards AGW then human error in not questioning acceptable to their theory data can enter as a bias in not checking thoroughly. Let us hope this will be a warning bell for all people dealing with data.

anna v

sorry that “oneness” should be “openness”. Something wrong with my dictionary click.

Neo

So was there really a noticeable pause in ice growth from December 12 to 19 caused by an anomalous atmospheric pressure pattern, or was that an early indicator of the sensor malfunction ?

Manfred

let’s hope the other satellite(s?) will continue to work this summer,
helping to prevent cruiseships from being stuck,
or prevent others from stupid ideas like kayaking through the recovering ice.

MattN

Well, I think they’ve found the source of the error…

Heraldo Ortega

quote – “an error known as sensor drift”.
Is that not known as – “FAILURE” ?.

F Rasmin

Anthony. I do not wish to belabour the point about the missing Canadian cities on the National weather map, but I look at the map everyday to get an idea how patterns of warm and cold move around over the American continent. I cannot recall ever seeing the Canadian stations missing. That is why I mentioned it. I did not think that Canada or the US had seceded from each other!

Dr Meier, I look forward to your posting here. I’m glad that we seem to be gradually cracking the issues that have led to so much irresponsible reporting on scary non-existent Arctic melt scenarios – at least, with regard to data integrity. I hope to see issues of media science reporting integrity, following on the heels of this.
Everyone, if you want some basic understanding of the Polar regions and the questionable Steig Antarctica paper and its 10-year genesis, enjoy Warming Antarctica by Paintwork and the rest of the page. We are all still learning.

Jerry

Clive (23:21:02) :
Since water has vastly greater thermal capacity than air the air temperature can safely be reckoned to depend on water temperature over any reasonable expanse of ocean (as we know well in the UK). Therefore although land air temperatures are indeed cold enough to freeze brass monkeys, let alone water, I’d guess that the arctic ocean could be “warm” due to currents, etc. and thus lead to less sea ice forming.
Good work all round on this story.

On February 16, 2009, as emails came in from puzzled readers, it became clear that there was a significant problem
Kudos to ICECAP and WUWT. Citizen scientist bloggers discovered and reported the erroneous readings. That is pretty cool. Thanks to the Internet, science is becoming a more public undertaking, a less esoteric and hidden away in laboratories process. That’s the trend, anyway, and it’s a very healthy one, IMHO.
Thank you, Anthony, for being a leader in this new wave, this new gestalt of science.

Neven

Thanks for actively moderating this thread, Anthony!

jmrSudbury

The http://www.swpc.noaa.gov/SolarCycle/ sunspot graph has been updated. — John M Reynolds

D. King

In the description of the sensor systems, they are described
as passive. I wonder why they don’t use a Multi Frequency
Synthetic Aperture Radar? SAR systems are very good at
seeing density differences regardless of weather, and with
the addition of CCD (coherent change detection) processing
they could yield some incredible animations. With Interferometric
Synthetic Aperture Radar and CCD processing you could watch
the ice grow and retard in 3D.
Sorry, this is a link to Wikipedia, but you’ll get the Idea!
http://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar

Abitbol

From NSIDC “We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice, which is based on the the consistent, quality-controlled data archive discussed above.”
For sure, when the error is this way… doesn’t change anything for them.

Malcolm

Do step changes in the past data suggest a change in Artic weather, as originally thought, or does it now indicate problems with the satellite intrumentation?
I know from exerience that equipment that suffers a catastrophic failure usually have a history of periodic problems leading up to that failure.
It may also be worth checking the algorithms to see how they handle problematic sensors.

Julius StSwithin

There is lesson here for all of us. Whenever doing a calculation if the answers are what one expects one tends to accepts them without checking; if they are not what you expect you check them. In this case NSIDC were expecting lower areas of Arctic sea ice and accepted the values for a long time. If the error had gone the other way, and showed higher areas of sea ice, we can be sure they would have been checked much sooner.

I would like to thank NSIDC and Dr Walt Meier for his candid explanation. Kudos.
I shall be watching the mainstream media with interest to look for erroneous reports of massive ice shrinkage beyond summer norms from now on with a better and more informed perspective.

Robert Bateman

Would there be any reason to suspect that increase in cosmic rays is going to lead to increased sensor erratica and/or failure?
i.e. – should we expect spaceborne sensors to show increased rates of failure?

Jørgen F.

“However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years. There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods.”
It’s of course understandable that using as many different data sources as possible enhances QA abilities and general data reliability within this field of science – thus in Meier’s obvious interest to keep the DMSP based data collection going.
Otherwise the statement is odd – very odd.

Mike C

something worth blogging about

“on February 15, 1979, global sea ice area was 16.79 million sq. km and on February 15, 2009, global sea ice area was 15.45 million sq. km. Therefore, global sea ice levels are 1.34 million sq. km less in February 2009 than in February 1979. This decrease in sea ice area is roughly equal to the area of Texas, California, and Oklahoma combined.
It is disturbing that the Washington Post would publish such information without first checking the facts.”
I remember that recently there was a discussion about the way coastlines have been redefined and this has led to a reduction in the area counted as sea ice. Has anyone come up with figures to compensate for changing definitions?

Julius StSwithin

Off topic (sorry) but I think important.
One of the alarmists’ oft’ repeated claims is that methane can provide a positive feedback mechanism. The earth warms: methane is released from the permafrost and elsewhere: methane is a GHG: more warming occurs: more methane is released….
The earth emits radiation in the long-wave band between 4 and 50 microns with a peak at around 12 microns. Methane absorbs radiation in a narrow band around 7 to 8 microns. Almost no radiation in this band escapes at present so extra methane would have negligible warming effect.
Am I missing something or is this correct?

Steven Horrobin

Neo-
While it may have been related to sensor malfunction, there is no question that there was a very strong and stable Southerly airstream through and to the West of the Norwegian Sea, which brought unseasonably warm air North, for a considerable period. This was caused by a stable High over North West Europe and Scandinavia, holding off a deep low in the Greenland area.
Perhaps a combination of both?
I am pleased that the (rather obvious in terms of effect on data) malfunctioning has been recognised, but sad that we may have lost an important data source. All good wishes to Dr. Meier and his colleagues in their endeavors to overcome this problem.

Pearland Aggie

well, I suppose the data doesn’t really matter anymore…
E.P.A. Expected to Regulate Carbon Dioxide
http://www.nytimes.com/2009/02/19/science/earth/19epa.html
this ought to be great for the economy! /sarc

Pierre Gosselin

I’ve noticed sea level charts have been updated:
http://sealevel.colorado.edu/current/sl_noib_global.jpg
I was wondering if this will be commented on soon.
Normally sea levels spike at the end of the year, and then drop at midyear. Can we expect a drop in the months ahead?
On the side, Ipersonally I wouldn’t mind if Anthony limited the comments to 500 words or something. I wonder how many really long comments actually get read. On this thread though, readers seem to be keeping them short.

I was certain that it was a mistake that they would find and kindly fix. Otherwise, the graph would be a proof of James Hansen’s tipping points, if not death trains. 😉
More quantitatively, the sea ice anomaly has never been decreasing for 1 month even by 30% of the amount/rate that was shown on the blue graph line. Such a tripling of the record rate of decrease would be a 5-sigma effect or so.
The null hypothesis that it was a fluke would be ruled out according to the conventional statistical criteria of verification in science.

mercurior

i am wondering what other sensors are degrading. Could it be more of the same for other systems. There is also a possibility of feed back as well..
There is a feeling that technology is stable, when it isnt as stable as it seems.

Pierre Gosselin

I’d like to apologise for the cheap shots I took in the recent-related thread.
But with the shenanigans we’ve seen from other circles, e.g. hockey stick, Antarctica, etc., I admit I got carried away, and the last time I shot from the hip without thinking. But no excuses.
With the media, institutions, bloggers, etc. diligently watching climate data, I’d still like to see institutions exercise far greater care in verifying data before making it public. The NSIDC’s disappearance of 1 million sq. km of ice should have thrown up a red flag. I still think they have to be more careful. It really does get down to their integrity.
All too often do the media run with “alarming news”, and then ignore subsequent corrections. This leads to public disinformation and bad policymaking. Personally I’m tired of paying through the nose for policy that’s based on junk data and panicked populations. For some of us, the nerves are getting a raw.

MattN

So, I guess it turns out this was indeed worth blogging about…

Mary Hinge

Pierre Gosselin (03:38:10) :
I’ve noticed sea level charts have been updated:
http://sealevel.colorado.edu/current/sl_noib_global.jpg
I was wondering if this will be commented on soon.

Check out earlier posts, this has been discussed a few times. This graph gives a more accurate view of trend with the seasonal signals removed and the inverse barometer applied. http://sealevel.colorado.edu/current/sl_ib_ns_global.jpg

Pierre Gosselin

I stopped looking at the NSIDC data a long time ago because I stopped trusting it…and maybe unfairly so.
But Leon makes a good point about the statement:
“There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods.”
So someone please tell me if my distrust is unfair.
It is openly admitted that the data is not accurate.