We’ve had two weeks of worrying news about the melting of Antarctica. The Larsen C and especially the remaining Larsen B ice shelves appear vulnerable to collapse, even as the glaciers of the Southern Antarctic Peninsula region have just been shown to be pouring large volumes of water into the ocean.
Most people, I think, would find this pretty alarming. However, as I wrote about these Antarctic news stories over the past two weeks, I became aware that those skeptical of human-caused climate change (whether its existence, or its severity) had found a new argument to minimize concerns about polar ice melt. In particular, I came across numerous citations of a much-read article at Forbes by James Taylor, titled “Updated NASA Data: Global warming not causing any polar ice retreat.”
There are many problems with this claim. In effect — and as we’ll see — Taylor is falling into a long climate “skeptic” tradition of pointing toward growing sea ice around Antarctica, and thereby suggesting that this trend undermines broader concerns about polar ice melt, or climate change in general. It doesn’t. (For another strong rebuttal to Taylor, see here from Slate’s Phil Plait.)
To support his claim, Taylor links to a recent visualization, based on NASA satellite data, of trends in global polar sea ice. Here is the figure, which was constructed by The Cryosphere Today at the University of Illinois at Urbana-Champaign:
As Taylor wrote, linking to this figure:
Updated NASA satellite data show the polar ice caps remained at approximately their 1979 extent until the middle of the last decade. Beginning in 2005, however, polar ice modestly receded for several years. By 2012, polar sea ice had receded by approximately 10 percent from 1979 measurements … In late 2012, however, polar ice dramatically rebounded and quickly surpassed the post-1979 average. Ever since, the polar ice caps have been at a greater average extent than the post-1979 mean.
Later, Taylor suggests that even if a “modest retreat” of polar ice — which he doesn’t think is happening — does arrive, we shouldn’t really worry about it. Such a decline “would not be proof or evidence of a global warming crisis,” he writes. “Such a retreat would merely illustrate that global temperatures are continuing their gradual recovery from the Little Ice Age.”
So can all of that really be right?
First off, the terminology being used in the passage above (“polar ice,” “polar ice caps”) is problematic. At most, the data above tell us about trends in ice covering the oceans of the polar regions, not frozen ice on land.
However, much of the concern with the melting of Antarctica, Greenland and glaciers around the world has nothing to do with sea ice — rather, it involves huge masses of ice sitting atop landmasses in polar regions. Melting of these ice sheets, glaciers and ice caps can contribute substantially to sea level rise —whereas sea ice melting cannot. So already, Taylor’s argument about “polar ice” seems much broader than it actually is.
And even when it comes to sea ice, the argument falters.
At Cryosphere Today, researchers have penned a rebuttal to Taylor, stating that contrary to his claim, there is a 5.5 percent downtrend in overall sea ice area over the period in question.
“It is misleading to claim that polar sea ice has not decreased over the historic record,” the site states. “In his last paragraph, Taylor correctly asserts that receding polar ice caps are an expected result of a warming planet. In fact, the data shows that this is exactly what is happening.”
And there’s another problem, explained the University of Illinois’ polar researcher Bill Chapman by phone. The figure above sums together sea ice trends in both the Arctic and the Antarctic, where different things are happening for different reasons. “The Arctic has decreased dramatically, and the Antarctic has increased a little bit over the same period,” Chapman said.
Taylor doesn’t appear to distinguish between what’s happening to sea ice in the Arctic and the Antarctic. But if you pull apart these two components of the analysis — as NASA itself has recently done — then sure enough, you find a sharp decline in Arctic sea ice, a modest increase in Antarctic ice, and an overall decline in total sea ice.
It’s important to stress how dramatic the Arctic sea ice decline is. Recent years have seen new lows for both winter and summer ice extent. “Data suggest that since , Arctic ice has been decreasing at an average rate of about 3 percent per decade,” observes the National Snow and Ice Data Center, “while Antarctic ice has increased by about 0.8 percent per decade.”
That uptick in Antarctic sea ice is what climate “skeptics” continue to focus on — and it’s a major subtext to Taylor’s argument. But the more you look into the matter, the more you realize it’s no consolation.
First, some scientists think growing Antarctic sea ice may actually have a human component — that global warming and ozone depletion have led to shifting winds that are fueling more ice growth. And second, a little added Antarctic sea ice doesn’t do anything to allay concerns about loss of ice from Antarctica’s continent. They’re just different issues.
For more on to why Antarctic sea ice has been increasing a little, even as the continent’s vast ice shelves and glaciers have mostly been doing the opposite — well, read here.
Most important of all, though, the case for worrying about what’s happening to the poles goes way beyond matters of sea ice loss (though that can have major consequences). The chief threat that the melting poles pose to the globe is the way they can raise sea level. We don’t know how much sea level rise we’re going to get, or how fast, from Greenland and Antarctica. But there are worrying signs from these ice sheets, and they contain enough potential water to dramatically alter coastlines the world over.
So in sum: 1) total (or global) polar sea ice is in fact declining, according to both NASA and the University of Illinois at Urbana-Champaign’s Cryosphere Today; 2) if you analyze the Arctic and Antarctic separately — which makes more sense to do, as very different things are happening to sea ice in the two places — you realize that the Arctic sea ice decline in particular is very stark; 3) there is also bad news about the melting of ice atop land, based on data that are completely outside of this discussion, but that are perhaps the most worrying of all.
So it is hard to find anything here that should make you not worry about global warming.
Also in Energy & Environment: