{"id":318547,"date":"2024-04-17T11:46:10","date_gmt":"2024-04-17T09:46:10","guid":{"rendered":"https:\/\/climatescience.press\/?p=318547"},"modified":"2024-04-17T11:46:13","modified_gmt":"2024-04-17T09:46:13","slug":"antarctica-is-colder-icier-now-than-any-time-in-5000-years-the-last-warm-period-was-1000-years-ago","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=318547","title":{"rendered":"Antarctica Is Colder, Icier Now Than Any Time In 5000 Years. The Last Warm Period Was 1000 Years Ago."},"content":{"rendered":"\n
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From NoTricksZone<\/a><\/p>\n\n\n\n

By\u00a0Kenneth Richard<\/a><\/em><\/p>\n\n\n\n

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More evidence emerges that Antarctica has undergone rapid glacier and sea ice expansion in recent centuries, in line with the long-term and recent Antarctic cooling trend.<\/strong><\/p>\n\n\n\n

West Antarctica\u2019s mean annual surface temperatures cooled by more than -1.8\u00b0C (-0.93\u00b0C per decade) from 1999-2018 (Zhang et al., 2023<\/a><\/strong>).<\/p>\n\n\n\n

Not just West Antarctica, but most of the continent also has cooled by more than 1\u00b0C in the 21st century. See, for example, the ~1\u00b0C per decade cooling trend for East Antarctica (2000 to 2018) shown in Fig. ES1 (right).<\/p>\n\n\n\n

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Image Source:\u00a0Zhang et al., 2023<\/a><\/strong><\/figcaption><\/figure>\n\n\n\n

According to a new study<\/a><\/strong>, about 6000 years ago Antarctica\u2019s Collins Glacier\u2019s frontline was a full 1 km southwest of its current extent. The frontline advanced to today\u2019s extent ~5000 years ago.<\/p>\n\n\n\n

\u201cPrevious studies proposed that 6000\u2009yr BP, the frontline position of the Collins Glacier was located 1\u2009km further south west than the present, and that the current frontline was first attained at approximately 5000\u2009yr BP.\u201d<\/em><\/p>\n\n\n\n

The glacier then continuously retreated south of the modern extent for another 4000 years, with peak ice loss 1000 years ago (as shown in the 1000-year \u201cProglacial lake environment\u201d image). In the last 1000 years this glacier has rapidly re-advanced back to the glaciated extent from 5000 years ago, which is in line with the sustained cooling trend ongoing since the Medieval Warm Period.<\/p>\n\n\n\n

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Image Source:\u00a0Piccini et al., 2024<\/a><\/strong><\/figcaption><\/figure>\n\n\n\n

Throughout the Holocene (Medieval Warm Period, Roman Warm Period, and earlier) and until a few hundred years ago (from ~7100 to 500 years before present), coastal Antarctica\u2019s Victoria Land (VLC) was substantially warmer than today. The Ross Sea was also sufficiently ice-free to allow for elephant seal populations (as large as ~200,000 individuals) to thrive at 73-78\u00b0S.<\/p>\n\n\n\n

Today, however, elephant seal populations \u2013 which require extended sea ice-free sea waters to breed, forage, and provide nourishment for their pups \u2013 can no longer subsist anywhere even remotely close to the coasts of the Antarctic continent. It is now too cold and the sea ice is too extensive.<\/p>\n\n\n\n

The substantially reduced number of remaining elephant seals existing today can only survive on subantarctic islands (South Georgia, Macquarie) at southern South American latitudes (~54.5\u00b0S) situated\u00a02400 kilometers<\/strong><\/a>\u00a0north of VLC (Koch et al., 2019<\/a><\/strong>).<\/p>\n\n\n\n

The \u201cgenetically distinct\u201d VLC elephant seal populations that endured throughout the Holocene and even through Medieval times have tragically died off in the last few centuries due to the modern-era cooling gradient and subsequent ice cover expansion (Hall et al., 2023<\/a><\/strong>).<\/p>\n\n\n\n

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\u201cAcross all sites, there is a precipitous drop in the number and geographic extent of the SES [southern elephant seals] remains within the last millennium\u201d<\/em><\/p>\n\n\n\n

\u201c\u2026the documented population crash and abandonment of the entire coast by SES after ~1000-500 yr BP was due to return of heavy sea ice\u201d<\/em><\/p>\n<\/blockquote>\n\n\n\n

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Image Source:\u00a0Hall et al., 2023<\/a><\/strong><\/figcaption><\/figure>\n\n\n\n

And with the modern sea surface temperatures cooling and southern hemisphere sea ice expansion in recent decades, even the subantarctic islands in the South Pacific that SES are limited to occupying today may not be sufficiently warm and ice-free to accommodate remaining populations. Today\u2019s southern elephant seals are thus ironically threatened by\u00a0cooling\u00a0<\/em>in the era of anthropogenic global warming.<\/em><\/p>\n\n\n\n

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\u201c[P]ack-ice expansion (both duration and extent) in the Ross Sea over the last several decades has been linked to reduced female foraging in this region, consequent low weaning weights and survival of pups, and ultimately the decline of the Macquarie Island population.\u201d\u00a0<\/em><\/p>\n<\/blockquote>\n\n\n\n

Interestingly, Hall et al. also report that not only have the last few centuries (including the present) been \u201cthe coldest, iciest conditions in the post-glacial period\u201d (see the blue sea ice and red temperature trend lines on the Holocene timeline), but even\u00a0the last glacial period<\/em>\u00a0had periods (~50,000 to 25,000 years ago) with less sea ice than today, allowing SES to occupy the VLC coast.<\/p>\n\n\n\n

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Image Source:\u00a0Hall et al., 2023<\/a><\/strong><\/figcaption><\/figure>\n\n\n\n
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