In recent years, one of climate change doubters’ favorite arguments has involved the floating sea ice around Antarctica. It’s growing, they contended — and that raises doubts about our understanding of human-induced climate change.

To this, climate scientists always responded: Not so fast. Floating sea ice in another cold place, the Arctic, is clearly shrinking, as are Arctic and Antarctic glaciers, and we don’t fully understand all the drivers behind the vast and complex Antarctic sea ice system. So don’t leap to the conclusion that odd behavior in floating Antarctic ice, which indeed has been growing slightly in recent years, undermines climate concerns.

Now, though, the argument for doubters just got even more complicated. After seeing a record high for total extent in the year 2014, Antarctic sea ice had been running very low in late 2016 and early 2017. And now, as of data recorded on Monday and Tuesday by the National Snow and Ice Data Center, the extent of Antarctic sea ice now appears to have hit a record low (although scientists still have to confirm this and have not made an official announcement yet).

It’s summer in Antarctica right now, and floating sea ice on Monday only covered 2.287 million square kilometers, according to “near-real-time data” from the National Snow and Ice Data Center. If that’s correct, that would barely edge out the previous record low of 2.290 million square kilometers on Feb. 27, 1997. The records go back to 1979.

On Tuesday, meanwhile, the ice extent shrank further down to 2.259 million square kilometers — underscoring the likelihood of a record, once the data is confirmed. Here’s an image, created using the center’s handy “Charctic” tool, showing this month’s ice (in light blue, below the others) compared with all other years in which we have data for Antarctic sea ice:

“Record low sea ice extent in the Arctic has, in a sense, become old news,” said Mark Serreze, director of the National Snow and Ice Data Center. “But now the Antarctic is getting into the act.  There are certainly many questions out there as to why Antarctic sea ice is also at a record low, but we can’t deny the reality that things are changing and they are changing fast.”

Sea ice is almost completely absent right now along the coast of West Antarctica in particular, a region where huge and fast-retreating glaciers have raised major concerns about potential sea-level rise. It’s unclear if lack of sea ice in the area might also signal that the oceans are having an effect on the continent’s marine-based glaciers.

It’s also important to note that it’s still only mid-February, so it could be that Antarctic sea will lose more ice before it begins to refreeze and expand again, according to its seasonal cycle. So what now appears to be a new record low may not be the record for very long. We will have to await a formal confirmation of all of this from the center, which may not come until the ice is clearly beginning to grow once again.

In the meantime, there are some interesting ideas out there about what explains the recent behavior of Antarctic sea ice. For instance, Gerald Meehl, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo., has published research suggesting that floating Antarctic ice is actually controlled in part by the state of the distant Pacific Ocean, whose influence on wind and weather patterns ultimately stretches all the way down to the Antarctic.

That study focused on a natural climate wobble called the Interdecadal Pacific Oscillation, or IPO, whose negative phase is one in which heat ends up getting buried in the Pacific Ocean, and whose positive phase unleashes it. The IPO was in a negative phase through much of the 2000s, but it may now be shifting back, Meehl says. And that could be playing a role in sea ice.

“It is consistent that a positive phase of the IPO could be associated with reduction of Antarctic sea ice extent, which is what is happening now,” Meehl commented by email. “However, given that the IPO is a decadal timescale phenomenon, and what we’re seeing now is a reduction of Antarctic sea ice that started sometime after the middle of 2016, we can’t say that Antarctic sea ice will stay at this low extent indefinitely. But the evidence from IPO connections is pointing in the right direction for a possible decadal trend toward reduced sea ice extent.”

In the end, since Antarctic sea ice was previously trending upward, the sudden reversal shouldn’t be a reason to turn on a dime and suggest that the ice is now declining — yet. Instead, it further underscores that we don’t fully understand what’s going on with this system. Which is precisely why it’s so dangerous to cite Antarctic ice to undermine the overwhelming evidence of climate change elsewhere.

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