“Truly the stuff of nightmares”: unprecedented low in Antarctic sea ice recorded
By Jeremy Smith, May 31, 2024, https://johnmenadue.com/truly-the-stuff-of-nightmares-unprecedented-low-in-antarctic-sea-ice-recorded/?fbclid=IwZXh0bgNhZW0CMTEAAR0LBw8Xpve2S05Os1FH_y7RYvvv8tqj0qhXrhsM-Z3e49hH1Uu2E44lQr4_aem_AbLMAUeHwooBl6H86wLEqHTtPllDKldX5fzB5e2_5LYTTkXQuf4y_brUHNORL5PsxpdKGuD227S1VVLTWCOjJj7N
Each winter the surface of the sea freezes around Antarctica, over a vast area, mostly to a depth of about one metre. But this is starting to change. Last year, the sea ice reached an unprecedentedly low maximum extent of only 17 million square kilometres.
Why aren’t we talking about sea ice? Perhaps it’s because most people haven’t even heard of it, which is a shame because it’s important.
Each winter the surface of the sea freezes around Antarctica, over a vast area, mostly to a depth of about one metre. The continent effectively doubles in size, with 18-20 million square kilometres being covered by floating ice. That’s an area 2.5 times that of Australia; 4% of Earth’s surface.
But this is starting to change. Last year, the sea ice reached an unprecedentedly low maximum extent of only 17 million square kilometres. Although this year looks like being a little less extreme, a clear and concerning trend appears to be under way. This is emphasised in the ice minimum values in late summer. By February each year the sea ice extent shrinks typically to about three million square kilometres (mostly in two large embayments, the Weddell Sea and the Ross Sea), but through most of the present decade it has dwindled to below two million.
Why does this matter? Well for a start, it is the underside of this huge area of sea ice where algae live and multiply, which feed the shrimp-like krill that in turn sustains an entire ecosystem: fish, seals, penguins, whales, the lot. The upper surface of sea ice is also crucially important. Its albedo, or reflectivity, means that 80-90% of the incoming summer sunshine is bounced back into space. Replace the ice with dark ocean and only about 9% is reflected, the rest going to warm the water. So the loss of sea ice is not only a symptom of climate change, it also contributes to it, in a feedback loop that might accelerate.
There’s more. When sea water freezes, the developing ice crystals comprise nearly pure water. Most of the salt is extruded as a heavy brine, and this cold, dense water sinks, becoming the Antarctic Bottom Current. This circulates around the Southern Ocean before spinning off into the other major ocean basins. As this deep cold flow moves north it displaces warmer water which then up-wells and forms the main surface currents. Without the annual ‘push’ of the Antarctic Bottom Current, these warmer currents might slow and cease.
The global ocean is so vast that it changes very slowly. We are only now beginning to see the results of the ocean’s absorbance of a century of industrial environmental heating, in the form of anomalously warm seas particularly this year. Any pronounced weakening of the ocean circulation due to sea ice loss will be slow – but inexorable.
The results, which are probably not going to happen in our own lifetimes but could well become part of our legacy to future generations, are likely to be dire. It could eventually mean goodbye to the Gulf Stream and the other currents which maintain benign climates on the European Atlantic coast, around Japan, and elsewhere in the northern hemisphere.
The possible consequences of such climate change for human societies are truly the stuff of nightmares.
Antarctic sea ice ‘behaving strangely’ as Arctic reaches ‘below-average’ winter peak
Carbon Brief, AYESHA TANDON, 26 Mar 24,
Antarctic sea ice is “behaving strangely” and might have entered a “new regime”, the director of the US National Snow and Ice Data Centre (NSIDC) tells Carbon Brief.
Following an all-time low maximum in September 2023, Antarctic sea ice has been tracking at near-record-low extent for the past six months. Last month, it hit its 2024 minimum extent, tying with 2022 for the second-lowest Antarctic minimum in the 46-year satellite record.
Dr Mark Serreze, director of the NSIDC tells Carbon Brief that more warm ocean water is reaching the surface to melt ice and keep it from forming. He says that we “must wait and see” whether this is a “temporary effect” or whether the Antarctic has entered a “new regime”.
Meanwhile, Arctic sea ice has reached its maximum extent for the year, peaking at 15.01m square kilometres (km2) on 14 March. The provisional data from the NSIDC shows that this year’s Arctic winter peak, despite favourable winds that encouraged sea ice formation, was 640,000km2 smaller than the 1981-2010 average maximum.
This year’s maximum was the 14th lowest in the satellite record…………………………………………………………………………………………………………………………………………………..
Record-breaking Antarctic extent
Antarctic sea ice has been tracking at or near record-low levels for months.
The Antarctic set a record-low maximum on 10 September 2023, with an extent of 16.96m km2. This was “the lowest sea ice maximum in the 1979 to 2023 sea ice record by a wide margin”, and one of the earliest, the NSIDC says.
Antarctic conditions over 2023 were “truly exceptional” and “completely outside the bounds of normality”, one expert told Carbon Brief.
As 2023 progressed, Antarctic sea ice melt was “slower than average”, the NSIDC says. The total decline in Antarctic sea ice extent through October was 903,000km2, while the October average was 985,000km2.
Nevertheless, Antarctic sea ice extent continued to track at a record low. On 31 October 2023, Antarctic sea ice extent was still tracking at a record-low of 15.79m km2. This is 750,000km2 below the previous 31 October record low………….. more https://www.carbonbrief.org/antarctic-sea-ice-behaving-strangely-as-arctic-reaches-below-average-winter-peak/
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