Iceberg surrounded by sea ice in Antarctica

Iceberg surrounded by sea ice in Antarctica. CREDIT: Eva Nowatzki, distributed via imaggeo.egu.eu

A new study finds that the change in the trend of Antarctic sea ice growth over time is “not as extreme as the published literature indicates,” as one coauthor put it.

The most important thing to know about Antarctica and ice is that a large part of the South Pole’s great sheet of land ice is close to or at a point of no return for irreversible collapse. Only immediate action to sharply reverse CO2 emissions could stop or significantly slow that.

And that really matters since 90 percent of Earth’s ice is in the Antarctic ice sheet, and even its partial collapse could raise sea levels tens of feet (over a period of centuries) and force coastal cities to be abandoned.

So you can imagine why the people who don’t want to take any action on climate change focus on floating Antarctic sea ice, which has been increasing (unlike Arctic sea ice, which has sharply declined). In particular, articles on Antarctic sea ice extent had reported an 8-fold jump in the rate of increase between 2000 and 2012.

For the dwindling number of people who seriously deny the objective reality of man-made warming, this is “proof” that their anti-scientific views are right. For the 97% of climate scientists (and world governments and others) who understand the reality of human-caused climate change, this is an intriguing puzzle to be solved.

In the reality camp, Skeptical Science reviews the scientific literature (here) and offers this summary explanation:

Antarctic sea ice has been growing over the last few decades but it certainly is not due to cooling – the Southern Ocean has shown warming over same period. Increasing southern sea ice is due to a combination of complex phenomena including cyclonic winds around Antarctica and changes in ocean circulation.

Now “The Cryosphere” has published a new study on “A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated?” (European Geosciences Union news release here).

The abstract explains:

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 … rather than a physical increase in the rate of ice advance.

The study found that this change in data processing “caused a substantial change in the long-term trend.” The authors note that “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.”

But one of the co-authors, Dr Walt Meier, a cryoscientist, explained to me that the climate scientist who maintains the data set for NASA has rechecked it — and found the error was in the original processing. In other words, “the most recent Antarctic sea ice trends are correct” but “the earlier published trends are incorrect and the change in trend over time is not as extreme as the published literature indicates.”

Bottom line: Antarctic sea ice trends are an intriguing scientific puzzle worthy of academic interest, whereas Antarctic land ice trends are like the planet running around with its hair on fire, yelling “stop the madness of denial and delay before it’s too late.”

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