One of the things climate change science deniers say, to throw you off, is that Antarctic sea ice is expanding. They even claim that the amount of expansion of Antarctic sea ice offsets the dramatic retreat of Arctic sea ice (see this for the latest on the Arctic). I've even seen it argued, in that famous peer-reviewed publication Twitter, that there is an inter-polar teleconnection that guarnatees that when the ice on one end of the earth expands the ice on the other end of the earth contracts, and visa versa, so everything is fine.
That Antarctic Sea ice is expanding has become standard knowledge. (See "Why is Antarctic Sea Ice Growing" for more.) It is a simple fact of nature that needs to be explained and addressed. The expansion of Antarctic Sea ice is one of the very few apparent reversals in climate change related trends across the world. And, there have been many explanations for it.
Or is it?
It turns out that we don't know if Antarctic sea ice is expanding. A new study just released looked at Antarctic sea ice to examine the idea, which has been batted around for a while now, that there is something wrong with the data. The study, by Eisenman, Meier, and Norris, published in The Cryosphere, found this:
Recent estimates indicate that the Antarctic sea ice cover is expanding at a statistically significant rate with a magnitude one-third as large as the rapid rate of sea ice retreat in the Arctic. However, during the mid-2000s, with several fewer years in the observational record, the trend in Antarctic sea ice extent was reported to be considerably smaller and statistically indistinguishable from zero. Here, we show that much of the increase in the reported trend occurred due to the previously undocumented effect of a change in the way the satellite sea ice observations are processed for the widely used Bootstrap algorithm data set, rather than a physical increase in the rate of ice advance. Specifically, we find that a change in the intercalibration across a 1991 sensor transition when the data set was reprocessed in 2007 caused a substantial change in the long-term trend. Although our analysis does not definitively identify whether this change introduced an error or removed one, the resulting difference in the trends suggests that a substantial error exists in either the current data set or the version that was used prior to the mid-2000s, and numerous studies that have relied on these observations should be reexamined to determine the sensitivity of their results to this change in the data set. Furthermore, a number of recent studies have investigated physical mechanisms for the observed expansion of the Antarctic sea ice cover. The results of this analysis raise the possibility that much of this expansion may be a spurious artifact of an error in the processing of the satellite observations.
It looks like, for sure, you can't say that Antarctic sea ice is expanding or contracting in its annual cycle. It also looks like the evidence suggests it is probably not expanding at all.
So, science, in its self correcting way, has thrown a wet blanket ... a warm and wet blanket perhaps ... on the idea that the Antarctic sea ice expansion disproves everything else we know about global warming. The Antarctic sea ice is not Galileo!
> numerous studies that have relied on these observations
> should be reexamined to determine the sensitivity of their
> results to this change in the data set.
Please keep track of such re-examinations when published.
I wonder how hard that is to do, and whether the original authors have to do it, or if others can take on the chore.
I suspect it will be a combination of those approaches, and I will keep track! Also, I would expect sites like Skeptical Science (http://www.skepticalscience.com/) will be updating.
When the measure the sea ice are the measuring the thickness too?
What do the people running these satellite measurments say to it?
I these are the people running the satellites, at least in part, or overlapping with them.
The satellite people are already involved. See also Screen in GRL 2011. He documented that a false trend some were noting was partly because, in an effort to get the best weather analysis of sea ice, I changed from Team1 to Team2 algorithm. Though my purpose was weather, some used it for climate. False trend ensued. I will work on a note for my blog tomorrow morning to cover more details about what is involved. Http://moregrumbinescience.blogspot.com
Ok, it'll be at http://moregrumbinescience.blogspot.com/2014/07/data-are-ugly.html 7 AM EDT,
If I understood correctly, there might be an error in processing satelite images, and coclusions about Antarctic ice expansion might be wrong!
But how does it relate to Arctic observations? Aren't those the same analysis methods and satelites? Does it mean that Arctic observations are also under question? Any clarification please?
Btw, I am not a climate change science denialist!
Filip, I think that is a very interesting and pertinent question. I think I might know the answer to it too, but I'm very busy this morning. I will try to get back to this later. The question brings up a lot of interesting aspects of the research.
Thank you very much Greg, I am looking forward to hearing your thoughts on the question.
Any thought on this? :)
Sorry, didn't ever get back to that.
The data are not really the same and the methods used are not either. There are many people that live in or near the sea ice region in the Arctic, lots of observation points, more aircraft, the shipping industry is always watching, etc. For example, pretty much every southward bound ice berg that forms in the North Atlantic is identified, numbered, and tracked. In the southern ocean, there are very few living people most of the year, and nowhere near the data on the ground. It is absolutely possible for some buoys or or sat data to be off in the southern ocean with very little ground truthing, and the data density is very different.
No problem Greg. Thanks a lot for the reply.
Thanks for the reminder!