This is a re-post from Yale Climate Connections by Bob Henson
The bloodless term “anomaly” doesn’t do justice to the stupendous temperature departures seen across parts of both the Antarctic and Arctic in mid-March 2022. With the initial shock now behind them, scientists are taking stock of exactly what happened and what it might portend.
The observations from both polar regions – especially the Antarctic – would be almost laughable if they weren’t so unsettling. Even as some of the scientists working in these remote areas shared humorous takes on the bizarre warm-ups, one could find plenty of angst, as temperatures in the Antarctic soared to levels that were in some cases virtually unthinkable just a few days beforehand.
The Arctic’s warm spell was impressive in its own right. An atmospheric river (or AR, a narrow plume of warmth and moisture that typically pushes toward higher latitudes) surged from the North Atlantic well into the Arctic Ocean on a track running just east of Greenland. The AR was associated with a powerful mid-latitude cyclone that produced the lowest atmospheric pressure ever recorded in Greenland: 934.1 mb at Ikermiuarsuk, beating a value of 936.2 mb set at two locations in 1986 and 1988.
As the AR pushed north, temperatures rose close to the freezing point near the North Pole. Several stations in Svalbard, Norway – an archipelago that includes one of the world’s northernmost cities, Svalbard – set all-time records for March, with readings as high as 42°F.
Not far from Svalbard, heavy rain was observed atop sea ice by an ongoing field project called HALO-(AC)³ designed to investigate such warm intrusions along with cold air outbreaks.
Even more impressive was the freakish warming at Earth’s South Pole. An atmospheric river originating near southeast Australia surged across much of the vast, barren landscape of East Antarctica, the coldest large plateau on the planet.
“This Antarctic heat wave definitely changes what we thought was possible for Antarctic weather,” tweeted Jonathan Wille (Université Grenoble Alpes).
East Antarctica doesn’t get gradual springs and autumns, to put it mildly. Instead, months of winter darkness switch abruptly into summers with near-constant sunshine and temperatures still frigid but far warmer than in winter. The winter cool-down arrives only a few weeks later.
In the case of March 2022, just days before the southern autumn equinox of March 20—a time when temperatures have normally plunged close to winter levels—the atmospheric river spread warmth-trapping clouds and moisture well inland across East Antarctica.
As a result, temperatures soared to levels as much as 50°F or more above average over broad areas on March 18 and remained far above average for several days.
The high temperature at Concordia Station, Antarctica, on March 18, 2022, soared above any temperature on record, even from midsummer, in data going back to 2013. (Image credit: Eric Lagadec, via ASTEP)
Pete Akers, a postdoctoral researcher at France’s Institut des Géosciences de l’Environnement, spent weeks at Concordia Station as part of a research expedition in the summer of 2019-20. Akers recounted his experiences in a series of guest posts for Category 6 (the predecessor of this blog).
“I think the biggest thing that people may not realize is just how hard it is to get really warm on the plateau outside of the 45 to 60 days surrounding the solstice [in late December],” Akers said. “The snow is so reflective that it doesn’t hold any heat, and there’s no rock for thousands of kilometers in any direction.”
Moreover, he added, “Concordia is 10,000 feet up and about 700 miles inland, so it’s rarely impacted by [storms] from the coast. The end result is generally a very consistent and stable temperature regime on a seasonal and day-to-day basis.”
By mid-March, when darkness is fast returning, “temperatures are typically almost at the winter minimum, not just halfway between summer and winter. So a proper comparison wouldn’t just be somewhere like Washington, D.C., breaking its all-time heat record in September—it’d be like breaking it in early November.”
Not all of Antarctica was basking in relative warmth. The atmospheric river didn’t extend as far inland as South Pole Station, where readings remained much closer to seasonal averages. Temperatures dipped below -60°C at the South Pole on March 21 even as highs at Vostok and Concordia rose above –26°C, readings that would have set monthly highs had they occurred at the start of the warm spell instead of well into it.
In an ironic twist, the “not-so-cold wave” brought massive amounts of snow to parts of East Antarctica. The atmospheric river squeezed out the snow from the unusually mild air, which was packing more than 0.50” of precipitable water (the amount of moisture in a vertical column of air), as the air was forced onshore and upslope against the high plateau.
The region’s snow cycle is driven largely by light accumulations balanced by sublimation (evaporation of snow into dry air), so this month’s heavy snow was a noteworthy infusion, countered only slightly by pockets of heavy rain and ice melt near the coast.
Based on model reconstructions, Xavier Fettweiss (University of Liège) estimated that March 17 was the Antarctic Ice Sheet’s fourth wettest day overall since 1980.
“Moisture intrusion events and atmospheric rivers — they do happen, but this is just to a different degree of intensity,” Wille told the Washington Post’s Capital Weather Gang.
Meanwhile, the sea ice that expands and contracts around the continent each year reached its lowest level in 43 years of satellite monitoring on February 25. Unlike the Arctic, the Antarctic had had no sustained decrease in sea ice extent for decades, actually setting consecutive record highs in 2012, 2013, and 2014.
A profound shift then followed, with 2017, 2018, and 2019 placing first, second, and third in sea ice extent minima until this year beat out 2017.
While the March warm blast in the Arctic was highly consistent with regional and global warming, the trends in Antarctica have been less straightforward.
Western Antarctica, and especially the peninsula extending north toward South America, have warmed dramatically since the mid-20th century, outpacing the rate of worldwide warming. By contrast, the South Pole and East Antarctica haven’t seen marked temperature rises in recent decades. One reason is the ozone hole. In the Antarctic stratosphere, human-caused ozone depletion (which is now gradually waning as a result of controls on ozone-depleting emissions) has led to an intensified polar vortex, which has helped to keep cold air pooled over the continent.
Although the atmospheric river of March 2022 was a historically extreme example, it’s not the only time such an amplified weather pattern has pushed warm air well inland across East Antarctica, according to veteran researcher John Turner of the British Antarctic Survey. Turner is lead author of an analysis published in February of an extreme warm-up fostered by an atmospheric river hitting the East Antarctic coast, together with warming induced by downslope flow, that occurred in the first week of December 1989 (just prior to the summer solstice).
“Incursions of warm air seem to be regular if not frequent occurrences,” Turner wrote in an email. “Why such high temperatures occurred [this month] across such a large area needs investigating once all the data have been brought together.”
There’s no obvious reason, other than the backdrop of general global warming, why the Arctic and Antarctic would happen to set such eye-popping warmth records within days of each other. The hemispheric climate regimes of north and south are largely distinct. Phenomena centered on the equator, such as El Niño and La Niña or the Madden-Julian Oscillation, can have impacts extending to both northern and southern latitudes. But scientists haven’t yet identified any single culprit that would be expected to cause such dramatic warm extremes near both poles at nearly the same time.
In fact, La Niña events, such as the one that’s been in place most of the time since 2020, tend to produce colder-than-normal seasonal averages in Antarctica, according to David Schneider, a National Center for Atmospheric Research expert on factors that shape Antarctic weather and climate.
Only a few months ago, the South Pole had its coldest average winter temperature (April-September) in 65 years of record keeping, with a six-month average of -78°F (-61°C).
Over the longer term, early-winter readings below -50°C at the South Pole have become significantly less frequent over the last couple of decades, according to a paper published in February and led by Linda Keller of the University of Wisconsin-Madison. (The decrease appears to have leveled off since the early 2010s, according to Stefano di Battisti, a coauthor on the paper.)
Above all, what the twin polar warmings reinforce is that, more than ever, we can expect the unexpected in a warming atmosphere. Wille likened the extremity of the Antarctic warm-up to the similarly out-of-bounds heat observed in the Pacific Northwest and British Columbia in the summer of 2021, with both occurrences seemingly implausible until they happened.
“For me, it’s hard to feel surprised by events like this anymore,” Schneider wrote in an email. He pointed out that studies of past climate indicate that, at times when atmospheric carbon dioxide concentrations were similar to their current values of around 420 parts per million, the Antarctic Ice Sheet was significantly smaller.
“How exactly [the ice sheet] loses mass, and how quickly it happens, are fascinating scientific questions,” Schneider wrote.
Speaking on a personal level, he added: “The question of ‘Will humanity do anything meaningful to slow down self-imposed rapid climate change?’ is a question that I grapple with daily.”
Posted by Guest Author on Wednesday, 30 March, 2022
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