For quite some time, climate scientists faced a conundrum: Even as the planet warmed, Antarctica's vast expanses of floating sea ice weren't shrinking. In fact, at times the ice was expanding, confounding common-sense and the predictions of sophisticated climate models.
Meanwhile, sea ice in the Arctic far to the north was shriveling dramatically, more or less as models predicted, and just as you'd expect in a warming world.
This stark discrepancy led climate change skeptics, and some media outlets, to proclaim that the Arctic and Antarctic were cancelling each other out — therefore, human-caused climate change was bunk.
For example, Andrew Montford, writing in the Daily Mail, noted that "for years, computer simulations have predicted that sea ice should be disappearing from the Poles." Growth of Antarctic sea ice at the time was a "mishap to tarnish the credibility of climate science." (Never mind that Montford, a registered accountant, had no credentials in climate science.)
Similarly, James M. Taylor, now president of the Heartland Institute, claimed in a Forbes opinion piece that Antarctica sea ice growth contradicted "one of the most frequently asserted global warming claims – that global warming is causing the polar ice caps to recede." (Taylor, who has provided this brand of analysis on many media outlets, including CNN, Fox News, and ABC, later saw his column yanked down by Forbes because it failed to meet the magazine's editorial standards.)
Arguments like this were disingenuous — and that's putting it kindly. They were much like saying dramatic deluges and torrential flooding in some places cancel extreme megadrought and raging wildfires in others, so there's nothing to see here, just move along.
But now, the Arctic and Antarctic are crying out in unison that there is very much something to see here.
Sea Ice in Antarctica Smashes a Record for Low Extent
In Antartica, sea ice naturally expands during winter until reaching a seasonal maximum, after which it shrinks with warming temperatures. In a recent update, the National Snow and Ice Data Center said the ice had reached that annual maximum extent on Sept. 10. At 676,000 square miles below the long-term average, it was a record low for the 45-year satellite monitoring era, according to the NSIDC. And it wasn't even close. The area of "missing" ice was slightly larger than Alaska.
This follows a record low minimum extent set at the end of the Antarctic summer back in February of this year.
As the animation above shows, 2023 has seen extraordinarily low sea ice extents for most of the year. "The extents this year have been far outside anything observed in the 45-year modern satellite record that began in 1979," the NSIDC said.
I emailed Walt Meier, an NSIDC senior research scientist, to put things in further perspective. Here's what he said: "For many years, the Antarctic was not generally extreme, except on the high side, and it had a small positive trend. Since 2016 that has largely flipped, with low Antarctic sea ice extent most months — but nothing that would indicate how extreme this year has been."
Meanwhile, in the far north, months of melting under the Arctic's long summer days and relatively warm temperatures caused sea ice there to reach its annual minimum extent on Sept. 19. While no new record was set, it nonetheless was the sixth lowest ever observed.
The Global Picture
When taken together, the extent of sea ice in the Arctic and Antarctic on September 30 was an astonishing 4,008,000 square kilometers (a little more than 1.5 million square miles) below the long term average.
That's an area of "missing" ice greater than half the land area of the contiguous United States.
Lumping together the Arctic and Antarctic extents like this does obscure the fact that these are different events occurring at opposite seasonal extremes — the end of summer in the north, and the end of winter in the south. Moreover, each region is quite different, both geographically and climatically.
The central Arctic region is an ocean surrounded by land. Because of the dynamics this sets up, it responds more directly to human-caused warming. Thus, with some ups and downs, the long-term trend has clearly been downward as the world has warmed — and the Arctic has warmed as much as four times as fast as the globe as a whole.
Meanwhile, the Antarctic is a large continent surrounded by ocean. This means it’s strongly influenced by shifts in winds and fringing seas, which result from a complex interplay of natural variability plus our influence on the climate system. As a result of this complexity, we can’t rule out a rebound in sea ice extent, even if temporary.
Even so, sea ice extent has declined so significantly in the Antarctic that scientists are worried it’s now following in the Arctic’s footsteps. As the NSIDC put, “There is some concern that this may be the beginning of a long-term trend of decline for Antarctic sea ice, since oceans are warming globally, and warm water mixing in the Southern Ocean polar layer could continue.”
For awhile, Meier was skeptical about reading too much into the global extent of sea ice. Again, that's because the Arctic and Antarctic are "independent, unconnected systems," he said. In his email, Meier also noted how climate skeptics would use shrinkage in the Arctic and growth in the Antarctic to argue that nothing concerning was happening.
Now that sea ice extents in both hemispheres are low, Meier doesn't find focusing on the global extent to be misleading. "It emphasizes the combined losses," he said.
Why Did Antarctica Defy Common Sense and the Models?
Even as human-caused warming of the planet was ongoing, why wasn't sea ice in the Antarctic shrinking for a time?
It turns out that variability of sea ice extent is quite significant in the Antarctic, in large measure because the continent is surrounded by open ocean. You can think of that variability as "noise" in the system, and it has been so large that it simply "washed out any 'signal'" from human-caused warming, Meier told me.
However, it was really just a matter of time before the Antarctic sea ice would respond to warming. As things turned out, and for reasons that aren't quite clear, that happened later than the models predicted. "But now the observations are quickly catching up to the models."
One thing the models failed to predict this year was the particularly sharp decline we've seen in Antarctic sea ice. For many scientists, that shrinkage has been just as shocking as the record warm ocean temperatures Earth has been experiencing at the same time.
The long and short of it is that both the cryosphere — the icy parts of the world — and the oceans, truly are trying to give us a message: Our impact on planetary life support systems is accelerating — and we ignore that at our peril.