Archives par mot-clé : Antarctica

Significant West Antarctic Cooling in the Past Two Decades Driven by Tropical Pacific Forcing

by X. Zhang et al., 2023, Apt 30, 2024  in BullAmerMeterologicalSoc


Abstract

During the second half of the twentieth century, the West Antarctic Ice Sheet (WAIS) has undergone significant warming at more than twice the global mean and thus is regarded as one of the most rapidly warming regions on Earth. However, a reversal of this trend was observed in the 1990s, resulting in regional cooling. In particular, during 1999–2018, the observed annual average surface air temperature had decreased at a statistically significant rate, with the strongest cooling in austral spring. The spring cooling correlates significantly with the second leading modes (EOF2) derived from empirical orthogonal function (EOF) analysis on the sea level pressure over Antarctica during 1999–2018, associated with the negative phase of the interdecadal Pacific oscillation with an average of cooling of central and eastern tropical Pacific surface sea temperature (SST) anomalies. The EOF2 results in the enhanced cold southerly winds on the continental WAIS through the cyclonic conditions over the Amundsen Sea region and a blocking high in the Drake Passage and northern Antarctic Peninsula, causing the WAIS cooling trend.

Antarctica Is Colder, Icier Now Than Any Time In 5000 Years. The Last Warm Period Was 1000 Years Ago.

by K. Richard, Apr 15, 2024 in NoTricksZone


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.

West Antarctica’s mean annual surface temperatures cooled by more than -1.8°C (-0.93°C per decade) from 1999-2018 (Zhang et al., 2023).

Not just West Antarctica, but most of the continent also has cooled by more than 1°C in the 21st century. See, for example, the ~1°C per decade cooling trend for East Antarctica (2000 to 2018) shown in Fig. ES

 

According to a new study, about 6000 years ago Antarctica’s Collins Glacier’s frontline was a full 1 km southwest of its current extent. The frontline advanced to today’s extent ~5000 years ago.

“Previous studies proposed that 6000 yr BP, the frontline position of the Collins Glacier was located 1 km further south west than the present, and that the current frontline was first attained at approximately 5000 yr BP.”

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 “Proglacial lake environment” 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.

No, CNN, Climate Change Is Not Driving Doomsday Glacier’s Decline

by S. Burnett, Mar 5, 2024 in ClimateChangeDispatch


A CNN story implies that supposed human-caused climate change is causing the Thwaites Glacier to melt, causing sea level rise. This is false.

Data show that Antarctica has not been warming. Also, the study CNN cited itself shows the glacier has declined dramatically and recovered repeatedly in the past, all without human contribution, suggesting the present decline is part of a natural cycle. [emphasis, links added]

At approximately the size of Florida, the Thwaites Glacier is the broadest glacier on Earth. The Thwaites Glacier is often referred to as the “Doomsday Glacier,” based on the belief that a complete collapse would cause as much as two feet of sea level rise over time.

The CNN story, “The ‘Doomsday Glacier’ is rapidly melting. Scientists now have evidence for when it started and why,” discusses a new study published in the journal Proceedings of the National Academy of Sciences, which determined when the present decline began.

“By analyzing marine sediment cores extracted from beneath the ocean floor, researchers found the glacier began to significantly retreat in the 1940s, likely kicked off by a very strong El Niño event — a natural climate fluctuation which tends to have a warming impact,” reports CNN.

“Since then, the glacier has been unable to recover, which may reflect the increasing impact of human-caused global warming, according to the report.”

Although the commencement of … Thwaites’ decline may now have been determined, any prognostications about future trends for the glacier are pure speculation, unsupported by historical evidence or data about present Antarctic trend.

The underlying reports determined that the Thwaites glacier’s decline commenced in the 1940s probably prompted by a powerful El Nino event that warmed the abutting waters.

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Antarctic Sea Ice Volume Greater Than The Early 1980s

by P. Homewood, Dec 21, 2023 in NotaLotof PeopleKnowThat


There was much scaremongering from the alarmist community when Antarctic sea ice extent fell earlier in the year. As the Antarctic summer begins, the melt has slowed down, to the extent that extent is not even the lowest since 1979, and it is higher than in 2017:

 

https://zacklabe.files.wordpress.com/2023/12/nsidc_sie_ant_lines-5.png

https://zacklabe.com/antarctic-sea-ice-extentconcentration/

But much more important is the fact that sea ice volume remains higher than the early 1980s, thanks to the fact that it is much thicker than normal around the peninsula:

New Study: Antarctic Sea Ice Completed Half Its Deglacial Retreat 1000s Of Years Before CO2 Began Rising

by K. Richard, Nov 16, 2023 in NotricksZone


The timing of the dramatic Antarctic sea ice decline during the last deglaciation suggests solar forcing and sea ice retreat “instigated” century-scale climate warming and atmospheric CO2 change. This would appear to challenge the perception CO2 plays a causal role in glacial-interglacial sea ice and climate changes.

From ~21,000 to 19,500 years ago, when CO2 was thought to have been at its lowest point in the Quaternary ice age (~180 ppm), the sea ice surrounding East and West Antarctica completed 50% of its eventual deglaciation-era decline (Sadatzki et al., 2023).

“[I]ndependent lines of evidence supporting that early sea ice and surface ocean changes in the Southern Ocean initiated as early as ~19.5 ka ago (with signs of summer sea ice retreat in our reconstruction as early as ~21 ka ago) and thus (at least) about 2 ka before major deglacial changes in global ocean circulation, climate, and atmospheric CO2.”

The increase in 65°S insolation during these millennia was deemed sufficient to drive this magnitude of sea ice retreat.

“This early increase in local integrated summer insolation at 65°S, which is independent of the longitude, may have thus provided enough energy to initiate melting of the near-perennial sea ice cover in late glacial.”

New Study Finds Most Of Antarctica Has Cooled By Over 1°C Since 1999…W. Antarctica Cooled 1.8°C

by K. Richard, Nov 6, 2023 in NoTricksZone


Significant 21st century cooling in the Central Pacific, Eastern Pacific, and nearly all of Antarctica “implies substantial uncertainties in future temperature projections of CMIP6 models.” – Zhang et al., 2023

New research indicates West Antarctica’s mean annual surface temperatures cooled by more than -1.8°C (-0.93°C per decade) from 1999-2018. In spring, the West Antarctic Ice Sheet (WAIS) cooling rate reached -1.84°C per decade.

Not only has the WAIS undergone significant cooling in the last two decades, most of the continent also cooled by more than 1°C. See, for example, the ~1°C per decade cooling trend for East Antarctica (2000 to 2018) shown in Fig. ES1.

Of 28 CMIP6 models, none captured a cooling trend – especially of this amplitude – for this region. This modeling failure “implies substantial uncertainties in future temperature projections of CMIP6 models.

 

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The post-1999 cooling trend has not just been confined to Antarctica. Sea surface temperatures (SSTs) in the Eastern and Central Pacific (south of 25°N) also cooled from 1999-2018 relative to 1979-1997. This cooling encompasses nearly half of the Southern Hemisphere’s SSTs.

Satellite Data Shows Antarctica Continues Adding Ice Mass, Lowering Sea Level

by Dr. M. Wielicki, Oct 19 2023 in Climate ChangeDispatch


 

Antarctica presented a more complex picture. While the continent as a whole lost about 130 gigatons of ice each year during a similar timeframe, the loss was most pronounced in West Antarctica, especially around the Amundsen Sea sector.

This accelerated melting in West Antarctica is a matter of particular concern for researchers, as it is claimed to have the potential to destabilize larger sections of the Antarctic ice sheet, leading to more pronounced sea-level rise in the future.

Mass change of the Antarctic Ice Sheet from April 2002 to September 2020. Time series of mass change from the GRACE and GRACE-FO missions, M(t), for the entire Antarctic Ice Sheet (green) and its division into East Antarctica (blue), West Antarctica (red), and the Antarctic Peninsula (yellow). The vertical lines indicate the end of the GRACE and the beginning of the GRACE-FO monthly data availability (June 2017 and July 2018, respectively). Shadings represent 1-σuncertainties. Equivalent sea-level contribution (right axis) is approximated as 1 mm sea-level rise for 360 Gt of ice mass loss. Source

However, since early 2020, nearly 1,000 gigatons of ice have been added to Antarctica. This remarkable ice gain represents nearly one-third of the total ice loss since 2002.