I assume that everyone has seen the post on our website discussing the changes that NSIDC has instituted to make our sea ice data available again. I don’t want to repeat that, but I thought I would respond to some of the more general issues that came up in Anthony’s posts and accompanying comments. I thank Anthony for giving me this opportunity. I write here from my personal viewpoint and not in an official capacity as a representative of NSIDC or the University of Colorado.
I apologize for the error in our data and for the relative slowness in responding to it. I’m glad that so many people are interested in the data and I understand that seeing errors is frustrating and can undermine confidence in the data. Anthony is correct that many people do now pay close attention to our website and we do have a responsibility to attend to errors as fast as we can. We will try to do better in the future. There are two major points that I hope everyone can take away from this event:
(1) The error in no changed any of our conclusions about the long-term changes in Arctic sea ice. The ice extent is declining significantly and the ice is thinning.
(2) Errors like the one that occurred are part of the normal course of dealing with satellite data. We hope that they are rare, but they are not unexpected.
On the first point, there is no doubt; it is verified by numerous independent observations and is well-discussed in numerous places, including in the entries on our analysis web page.
On the second point, I think it is worth providing some background on satellite data and how it is processed, stored, and used by scientists, including those at NSIDC. In doing so, I’m not making excuses for the error in NSIDC’s data, but I hope I can help people understand how such errors are part of the scientific process of quality controlling and fine-tuning data and techniques to ultimately provide the best information possible to track climate change.
Climate science is focused on understanding long-term changes and the mechanisms that drive them. In terms of satellite data, this means taking great care and making the data as good as it can possibly be. The focus is on assuring a time series good enough to track potentially subtle trends. This involves careful quality control of data and developing and fine-tuning algorithms to convert raw satellite data into a useful climate parameter (such as sea ice extent). Like all of science this has traditionally been done slowly, methodically, and privately. And up until about ten years ago, there was no other choice but to move slowly because of severe constraints on computer processing speeds, limited data storage capacities, and difficulties in simply sharing data. One of the earliest papers to note the long-term decline in Arctic sea ice was published in 1999 (Parkinson et al., J. Geophysical Research); it was based on data only through 1996. It simply took that long to collect and carefully analyze the data, make sure algorithms were robust and stable, and get a paper through scientific peer-review.
Data distribution was also limited because of similar computational, storage, and distribution constraints. For example, NSIDC used to received updates every five years or so of final quality-controlled sea ice products. We would then distribute the data by mail on CD-ROM only to registered users.
Immediate data analysis was solely the province of operational centers, like the National Weather Service, who had special access to near-real-time data. Their focus was on getting only what was needed of any data before moving on to the next analysis or forecast cycle. Quality control was focused on catching major errors; smaller errors that didn’t significantly impact a short-term analysis were not caught or were ignored. There was no consideration given to the long-term context of the data, which were often not even saved.
There was a very clear delineation between science and operations.
Science is still done slowly and methodically, with final results disseminated the way they always have been – through peer-reviewed scientific journals. It still takes time to do final quality control on climate products. NSIDC now receives final sea ice data about once a year. But in the past ten years or so, access to data has changed dramatically. Computer processing power and data storage capacities have increased exponentially and high-speed internet has allowed near instantaneous distribution of data to a broad community. Satellite data that used to require days or weeks of processing and required dozens of tapes or CDs to store can now be processed in minutes, stored on a portable hard drive or even a memory stick, and distributed over the internet. This has been a boon to scientists who now have much faster and easier access to large amounts of data.
At the same time algorithms have matured and become more stable. This means that significant adjustments to the algorithms are not regularly needed and they can be run confidently on near-real-time data, with the understanding that the results may change during final quality-control. This has allowed to NSIDC implement a near-real-time version of the sea ice data. For the past several years this data has been freely distributed online for anyone who wished to use it, though the primary audience was scientists who would be familiar with associated caveats of using near-real-time data.
In this context, let me now move on to NSIDC and its Arctic Sea Ice News and Analysis web site. NSIDC is a science institution. Our mission is science and science support, not operational support for any kind of critical operational decisions (e.g., what regions are free enough of sea ice to be safely navigated). Because we must focus on science, the resources we can devote to near-real-time data production and analysis are limited. Nonetheless, as climate change became an important topic, it was clear that Arctic sea ice was a leading indicator of the observed changes. Since NSIDC stores and distributes the sea ice data, many people started to come to NSIDC scientists to ask about sea ice conditions and the implications for the climate. When 2005 set a record low summer extent, there was a lot of media attention; in response we issued a press release. Through summer 2006 we received many requests asking about how the ice was looking, both from the media and fellow scientists. As the summer wore on it started to feel a bit like being on a family road trip and having the kids in the back continually asking “are we there yet?” As summer 2007 started, it was a clear that a new record low was quite possible. The questions began again in earnest.
In the sense that science ultimately serves society, it was becoming apparent that scientists and the public were coming to expect a near-real-time analysis of Arctic sea ice conditions. In response, we decided to develop the website so that we could post occasional data updates and science-based discussion of the conditions. This worked quite well, but the summer of 2007 was so remarkable and Arctic sea ice had become such a big story both scientifically and in the public consciousness that we realized there would be the expectation to do even more during 2008. In response, in addition to our occasional summer posts of data and analysis, we decided to provide daily data updates and at least monthly analyses throughout the year. This decision was possible only because the products are mature and stable and further quality control to produce final data results in only minor changes. This was an added burden on NSIDC resources, but with automated processing the day-to-day impacts could be managed.
This all evolved in an ad hoc manner, with improvements made when we had resources available. Remember, none of this is NSIDC’s primary mission, which is to archive hundreds of cryospheric datasets and support peer-reviewed research. The sea ice analysis website is one of dozens of research and data management projects at NSIDC. People working on the web site often have to fit it in where and when they can amid other duties. There is no single person at NSIDC who works only or even primarily on the sea ice analysis page. This is not an ideal situation, but it is the only way we can support the analysis while still fulfilling all of our responsibilities.
This is one reason why we appeared slow to address the error last week. We have a group at NSIDC whose responsibility is to respond to user questions and comments on any of our hundreds of datasets. NSIDC’s standard is to provide a response to user inquiries within 24 hours during the business week. This is very quick for a science institution and NSIDC’s user services works very hard to always meet that standard. However, it is not particularly fast compared an operational center that works on a 24/7 schedule. We will work to put into place better QC measures and more streamlined procedures to catch future errors more quickly, but we simply do not have the resources to work in an operational environment.
This of course begs the question: why don’t operational centers do this instead of NSIDC? Operational centers do indeed provide near-real-time sea ice data. However, I believe there are a couple reasons why operational centers are not poised to provide the kind of science-based support found at NSIDC. First, their only priority is on supporting critical users with the most useful operational information about sea ice – e.g., ships sailing in and near ice-infested waters; their data is not well-suited for easy understanding by a general audience. Second, operational centers are focused on near-real-time support, not on climate issues. Thus their expertise in putting near-real-time data in the context of long-term climate is limited.
NSIDC and other climate data/research centers (e.g., NASA GISS) do have that expertise. And that is crucial. It is only through evaluation of the near-real-time data in the context of the long-term climate that one can properly assess the relevance to climate change. This mixture of climate science and near-real-time data analysis is perhaps not optimal, but I think it is worthwhile.
The easy access to climate data has been a boon for scientists and I would argue it has also been a great benefit for society. Science ultimately serves society and quick and easy access to data provides quality up-to-date information on important issues, such as climate change. The problem is that such data can come to be viewed by journalists and other members of the public as completely routine and reliable. When small changes or errors occur, they may be given greater import than they deserve in terms of what they imply about climate change. This means there is a responsibility for places like NSIDC distributing data to thoroughly explain the data and respond quickly to any issues. I believe NSIDC does an excellent job in explaining the data through considerable documentation on all aspects of the sea ice data. However, in terms of responding to data issues, NSIDC and like centers have been slow to realize that the audience for such data has expanded beyond fellow scientists and informed journalists and that any issues need to be addressed as soon as possible lest they confuse or mislead the public. This is a difficult task for places like NSIDC, whose resources are limited and whose primary mission is not operational support. The recent data error has been a learning experience for those of us at NSIDC and we will try to do better.
I hope that this information gives people a greater appreciation for the hard-work done by my colleagues at NSIDC and an understanding of the difficulties inherent in supporting near-real-time data with limited resources amid myriad other responsibilities. Finally, I hope that people come away with a better sense of what goes into analyzing satellite data and how such data is so beneficial to our understanding of climate. Thank you.
Walt Meier
Thank you Dr. Meier for your essay and for your open dialog. It is a breath of fresh air compared to some other researchers.
Readers should note that over the past year, we have worked to develop a rapport with Dr. Walt Meier at NSIDC, who three times now on WUWT submitted thoughtful responses to some of our favorite Arctic questions.
I’d like to ask you Dr. Meier, about George Will’s recent column, which has been attacked by press, bloggers, pundits, and politicians like John Kerry who recently opined that George Will’s statement below is wrong.
Dr. Meier is George Will correct? And if not how far off the mark was he? Thank you for your consideration, Anthony Watts
PS. In an email to me Dr. Meier suggested to me that I should check out Andy Revkin’s writeup on it. I’m sharing the link he passed on to me for my WUWT readers:
http://dotearth.blogs.nytimes.com/2009/02/27/expers-big-flaw-in-wills-ice-assertions/
An excellent and informative response.
Personally, I had no issue with the recent data error. But, I do agree that, in today’s environment, errors such as that one can cause trouble. Even worse, are errors that are not so obviously errors. But, your response gives me cause to believe your establishment will do its best to provide accurate information — something I had no real cause to doubt.
Dr. Walt Meier:
F13 X F15
I have the impression that it was a simple exchange.
Sorry I did not understand.
Dr. Meier–
Thank you for taking the time to write this article. I think we all are grateful for the hard work you and your colleagues do in gathering, analyzing and making this data available, and we do understand that stuff happens sometimes. With an undertaking this big, it’s a credit to you that these things don’t happen much more often.
I really think Anthony’s first blog post wasn’t a “these guys screwed up” kind of post; it was a “Hey, there’s something here that needs attention”.
Thanks for all your hard work.
“(1) The error in no changed any of our conclusions about the long-term changes in Arctic sea ice. The ice extent IS declining significantly and the ice IS thinning.”
i would say “has been”.
(Hadley Center: “Indeed, the record-breaking losses in the past couple of years could easily be due to natural fluctuations in the weather, with summer sea ice increasing again over the next few years.”)
(NASA about summer 2007: “Unusual atmospheric conditions set up wind patterns that compressed the sea ice, loaded it into the Transpolar Drift Stream and then sped its flow out of the Arctic”)
Thanks Dr. Meier, your efforts are appreciated. I hope the NSIDC will not take criticisms too close to heart and stop providing the real time service you do.
I have processed your gridded data myself both daily and monthly, I consider the statement of “The ice extent is declining significantly” to be a bit strong. I’ve seen the loss and it isn’t much, however it is only my opinion. Your site stated,
“By mid-February, the difference had grown to 500,000 square kilometers (193,000 square miles), which is outside of expected error. However, that amount represents less than 4% of Arctic sea ice extent at this time of year.”
I found this to be fairly humorous as the total global sea ice ‘AREA’ decline over 30 years is only about 4% by data I downloaded from NSIDC.
Either way, please don’t take my comments too harshly because they aren’t meant to be. Your group has a high degree of professionalism and I wish it existed more often in climatology.
I wonder if you could answer a question, I saw in January 03, 2009 data the Hudson bay area – pre correction showed partial ice fill in some cells (<100%). I had the opportunity to overfly the bay only two weeks prior and the ice was completely packed as far as I could see. There was quite clearly 100% coverage.
Was this an artifact of the sensors, or am I missing something?
Dr Meier, thanks for the information; I don’t think there is any need on your part to apologize for a sensor going bad, and really do appreciate the hard work done by your organization. If you have a minute, a few observations/questions about the writeup on NSIDC:
However, that amount represents less than 4% of Arctic sea ice extent at this time of year.
I know that this is a 2009 delta, but isn’t 4% about the same amount that this years extent is below the 1979-2000 average? I don’t think (or know if, or care, really) that you wrote the 2/26 update, but it seems a bit conflicting for the NSIDC to be pooh-pooh’ing a 4% sat sensor area, when at the same time emphasizing a 4% decline from average. Just one of those things that raises eyebrows, I guess.
Also – it seems that (and please correct me on total area of potential cap) that the areas considered ice vs. land in the cryosphere have shrunk over the last 10 years. Not a lot, but enough to induce “decreased arctic ice cap” – this is totally based on eyeballing maps of ice cover on my part – it would be interesting to see (for the several regions/seas tracked, and especially those in northern Russia and Hudson Bay) the total area extent available, by year, for seas completely bounded by land and other seas tracked. The rivers seem to be shrinking in width, and some shorelines seem to have advanced into the sea. Again, that is just based on eyeballing, and I haven’t done my due diligence to get the data and plot it – one of those things that stays on the list but never seems to get done.
Again, thanks for all of your work and information on this issue.
(1) The error in no [way] changed any of our conclusions about the long-term changes in Arctic sea ice. The ice extent is declining significantly and the ice is thinning.
I am not comfortable with this statement. If the data (good or bad) doesn’t affect the conclusions, what does?
Below is George Will’s response to the Andy Revkin blog which Dr. Meier referred to. We really could benefit from a professional opinion, as George Will points out many problems in the Revkin response. Andy Revkin is a journalist like George Will – not an Arctic expert like Dr. Meier.
http://www.washingtonpost.com/wp-dyn/content/article/2009/02/26/AR2009022602906.html
Climate Science in A Tornado
By George F. Will
Friday, February 27, 2009; Page A17
Few phenomena generate as much heat as disputes about current orthodoxies concerning global warming. This column recently reported and commented on some developments pertinent to the debate about whether global warming is occurring and what can and should be done. That column, which expressed skepticism about some emphatic proclamations by the alarmed, took a stroll down memory lane, through the debris of 1970s predictions about the near certainty of calamitous global cooling.
Concerning those predictions, the New York Times was — as it is today in a contrary crusade — a megaphone for the alarmed, as when (May 21, 1975) it reported that “a major cooling of the climate” was “widely considered inevitable” because it was “well established” that the Northern Hemisphere’s climate “has been getting cooler since about 1950.” Now the Times, a trumpet that never sounds retreat in today’s war against warming, has afforded this column an opportunity to revisit another facet of this subject — meretricious journalism in the service of dubious certitudes.
On Wednesday, the Times carried a “news analysis” — a story in the paper’s news section, but one that was not just reporting news — accusing Al Gore and this columnist of inaccuracies. Gore can speak for himself. So can this columnist.
Reporter Andrew Revkin’s story was headlined: “In Debate on Climate Change, Exaggeration Is a Common Pitfall.” Regarding exaggeration, the Times knows whereof it speaks, especially when it revisits, if it ever does, its reporting on the global cooling scare of the 1970s, and its reporting and editorializing — sometimes a distinction without a difference — concerning today’s climate controversies.
Which returns us to Revkin. In a story ostensibly about journalism, he simply asserts — how does he know this? — that the last decade, which passed without warming, was just “a pause in warming.” His attempt to contact this writer was an e-mail sent at 5:47 p.m., a few hours before the Times began printing his story, which was not so time-sensitive — it concerned controversies already many days running — that it had to appear the next day. But Revkin reported that “experts said” this columnist’s intervention in the climate debate was “riddled with” inaccuracies. Revkin’s supposed experts might exist and might have expertise but they do not have names that Revkin wished to divulge.
As for the anonymous scientists’ unspecified claims about the column’s supposedly myriad inaccuracies: The column contained many factual assertions but only one has been challenged. The challenge is mistaken.
Citing data from the University of Illinois’ Arctic Climate Research Center, as interpreted on Jan. 1 by Daily Tech, a technology and science news blog, the column said that since September “the increase in sea ice has been the fastest change, either up or down, since 1979, when satellite record-keeping began.” According to the center, global sea ice levels at the end of 2008 were “near or slightly lower than” those of 1979. The center generally does not make its statistics available, but in a Jan. 12 statement the center confirmed that global sea ice levels were within a difference of less than 3 percent of the 1980 level.
So the column accurately reported what the center had reported. But on Feb. 15, the Sunday the column appeared, the center, then receiving many e-mail inquiries, issued a statement saying “we do not know where George Will is getting his information.” The answer was: From the center, via Daily Tech. Consult the center’s Web site where, on Jan. 12, the center posted the confirmation of the data that this column subsequently reported accurately.
The scientists at the Illinois center offer their statistics with responsible caveats germane to margins of error in measurements and precise seasonal comparisons of year-on-year estimates of global sea ice. Nowadays, however, scientists often find themselves enveloped in furies triggered by any expression of skepticism about the global warming consensus (which will prevail until a diametrically different consensus comes along; see the 1970s) in the media-environmental complex. Concerning which:
On Feb. 18 the U.S. National Snow and Ice Data Center reported that from early January until the middle of this month, a defective performance by satellite monitors that measure sea ice caused an underestimation of the extent of Arctic sea ice by 193,000 square miles, which is approximately the size of California. The Times (“All the news that’s fit to print”), which as of this writing had not printed that story, should unleash Revkin and his unnamed experts.
Thanks for the post Dr. Meier.
It should also be noted too that the Monday on which this occured was a US holiday.
Thanks, Dr. Meier!
It is always refreshing to deal with someone who in the academic field who actually want to convey information to a wider public rather than play chief high priest and obscure it. Your straight-forward approach is much appreciated.
Steven Goddard (15:31:13) :
George will quotes Revkin:
Which returns us to Revkin. In a story ostensibly about journalism, he simply asserts — how does he know this? — that the last decade, which passed without warming, was just “a pause in warming.”
*************
So does that mean that warming is just “a pause in cooling”?
Thanks for the update Dr Meier,
From your page
“Before acquiring data from F15, NSIDC obtained sea ice data from the SSM/I sensors on the DMSP F8, F11, and F13 satellites. In March 2008, we switched from the F13 satellite to the F15 satellite because the F13 SSM/I sensor had started to have regular areas of missing data. The missing data were caused by malfunctioning data recorders on the satellite, not because of any problem with the sensor itself. At the time, we were concerned that the recorder problem would become more serious. However, the F13 data recorders have not degraded further.”
Could you explain how the malfunctioning data recorder problem has been overcome? And if this problem persists, could you explain the adjustment/work around?
Walt Meier should be awarded some kind of WUWT gold star for at least addressing criticism. Good for him. Smart.
It is also a hymn of praise to the internet, although he doesn’t say as much. But, he realises that now, with the data being made instantly public, there are a thousand-fold number of data quality checkers available than his budget will allow.
Anyhoo, Walt Meier, hat off to you sir!
Thanks for the update.The use of NSIDC data by CT in an obviously biased way has not been addressed. Also, I do not believe that “death spiral” is in any way whatsoever a scientific description of the state of sea ice. George Will was obviously relying on the presented data.
Mike Bryant
I find it nonsensical that the debate concerning ice area extent is continuing. Is there not a dataset from 1979 that can be compared to a dataset from 2009 to determine the ice area coverage at two points in time? There must be definitive data or photographs somewhere, that both sides agree are correct, that can resolve this issue.
I am very glad Dr. Meier responded. With so few willing to step into the fire and debate these days, it is certainly refreshing.
That being said, I hope the good Dr. is not so set in his opinion that he does not entertain the idea that his conclusions may be wrong. That his data may be suspect. That perhaps he looks like he is towing a party line, or an agenda line.
I would feel alot better if Dr. Meier had a disclaimer something along the lines of:
“While the data our organization has collected seems to point in this direction, we certainly do not want to say the science is settled. There is much more research to be done, and definitive statements do more harm than good.”
Dr. Meir, Thank you for your response.
I do have a question about your comment #1. You state that the arctic ice is thinning. I just spent a little time searching for a link on ice thickness but I cannot find anything that is current. Are there current measurements available?
Thanks Anthony posting my response.
In regards to George Will, I appreciate your inclusion of the link to Revkin’s
response. I think he does a good job of explaining the issues in a clear
way, so I don’t have much to add. Basically, Mr. Will made three mistakes:
1. He was factually incorrect on the date that he reported his “daily
global ice” number. However, he was merely out-of-date with his facts
(it was true on Jan 1, but wasn’t 6 weeks later). This is somewhat
nit-picky, though it illuminates how fast things can change in a
relatively short period of time, meaning that one should be very
cautious about drawing any conclusions about climate from an isolated event.
2. Related to that, it is easy to cherry-pick one date here and one date
there to compare to support most any view. The important thing is to
look at things in the context of long-term changes. That is what NSIDC
always tries to convey by comparing to long-term averages.
3. “Global sea ice” simply has no meaning in terms of climate change.
The Arctic and Antarctic are unique and separated environments that
respond differently. It would be like taking a drought in Georgia and
torrential rain in Maine, adding those up and claiming that “rainfall is
normal” in the eastern U.S.
On the initial comments to this post, I’m glad that people appear to be understanding. I doubt I’ll have time to respond further to specific issues that come up in the comments, but I do see that NSIDC’s “only 4% too low “description has drawn some questions, so let me address that briefly.
The reason to point out the 4% number is that that is within what we might’ve expected from reasonable year-to-year variability. In hindsight, it was quite obvious that data was in error, but initially, while the numbers were low, they weren’t unrealistic.
This points out the important distinction between looking only at single data points vs. long-term trends. +/-4% at any given time is not particularly a big deal. On the other hand, January sea ice has declined at a rate of 3.1 % per decade, or roughly 10% overall since 1979. This is significant. Similarly, September ice cover has declined at a rate of over 11 % decade, or more than 30% overall since 1979.
Now, September 2007 did get a lot of attention as a single data point because it was so far off anything expected. As some have pointed out, a “perfect storm” of conditions contributed to this event, e.g., strong winds, clear skies, warm temperatures – all things attributable to short-term weather, not necessarily long-term climate trends. However, similar conditions have occurred in the past, but did not lead such a dramatic reduction in the ice extent. So why did they in 2007? It was because the long-term decline in the Arctic sea ice – extent, and particularly thickness – made the ice cover more vulnerable to extreme weather events.
I hope this helps further clarify a couple of issues. I’m sorry again that I probably won’t be able to respond to any other specific comments or questions.
Thank you.
Walt Meier
NSIDC
“I apologize for the error in our data and for the relative slowness in responding to it.” -Good.
“We will try to do better in the future.” -Hmmm.
“The ice extent is declining significantly and the ice is thinning.” -Data?
“The focus is on assuring a time series good enough to track potentially subtle trends.”-Is it “good enough”? That seems like a very low bar.
Did we ever learn if this is really a voluntary effort?
How about talking to people who live in Arctic Canada/N. Shore Alaska. I think they are experiencinging something entirely different to the satellite information described.
“The ice extent is declining significantly”
– shouldn´t be better to use term “minimum summer ice area is declining significantly”? Ice -is- declining significantly every spring-summer and growing every autumn-winter. Sometimes I think people imagine that the icecap is one big steady ice cake which is getting a bit smaller every year. We know how it is, but not sure with ordinary news readers. Otherwise thanks from Europe for interesting insights.
Walt,
Thanks for your response.
From a quick eyeballing of the UIUC graph, it appears that global sea ice area has been well within one standard deviation of the mean for all of 2009, not just on January 1. This would be considered normal. So I would say that George Will was correct about global sea ice.
http://en.wikipedia.org/wiki/Normal_distribution
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg
It also appears clear that Arctic ice area did make it’s greatest recovery in the satellite record during last winter, as George Will mentioned.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.jpg
In my view , on all counts George Will was correct. He did not discuss long term trends, and regardless I am not convinced that 30 years is a long enough record to determine if the trend is linear or cyclical. I suspect not. We do know that ships made it closer to the pole in open water 70 years ago, than Lewis Pugh made it last summer.
A toast to Dr. Meier! And a bet of 1,000 quatloos that she doesn’t thaw as much this summer.
OK, just one more, because Gary P brings up a good point about thinning of the ice cover.
Complete data is very hard to come by. Ice thickness is a very difficult thing to measurements. However, from submarine sonar measurements, ground measurements, more recent satellite measurements (since 2003), it is pretty clear that ice has been thinning quite substantially for a long time and the thinning has accelerated. One of the easier ways to at least get a sense of ice thickness is to look at ice age, which is much easier to track. First-year ice, ice that has formed since the end of the previous melt season, can only grow to about 1-1.5 m (3-5 feet) during the winter. Multiyear ice, ice that has survived at least one summer melt season and can continue to grow in subsequent winters, can get much thicker, up to 3-4 m (10-15 feet) thick or even more. Older multiyear ice is on the high end of that scale, while younger multiyear ice is closer to first-year ice values.
It is quite clear that there is much less multiyear ice than there used to be. We’ve discussed this from time to time on NSIDC’s news and analysis site, for example:
http://nsidc.org/arcticseaicenews/2008/040708.html