[clif]

OK...who is the "denier" here?

To answer your question,

consult your closest mirror ....

[Azothius]

Sudden warming over Antarctica to prolong Australia drought


https://www.yahoo.com/news/sudden-warmi ... 20967.html

A rare phenomenon causing "the strongest Antarctic warming on record" is set to deliver more pain to dought-stricken Australia, scientists said Friday.

The unusual event, known as "sudden stratospheric warming", started in the last week of August when the atmosphere above Antarctica began heating rapidly, scientists at Australia's Bureau of Meteorology said in a report.

"The Bureau of Meteorology is predicting the strongest Antarctic warming on record, likely to exceed the previous record of September 2002," it said.

The upper atmosphere above the South Pole has heated up from close to minus 70 to about minus 25 degrees Celsius, bureau climatologist Andrew Watkins told AFP.

"It has leapt up more than 40 degrees warmer than normal in the course of three weeks," he said.

Watkins said the uncommon occurrence was not believed to be linked to global warming.

The occurrence is triggered by a mix of "disturbances" in weather patterns closer to the ground, he added.

Sudden stratospheric warming is common in the northern hemisphere but has only been recorded on one other occasion, in 2002, in the southern hemisphere.

But is it amplified by global warming? Perhaps something to watch for, if it's frequency of occurrence increase?


How this affects Australia:

The rapid warming slows down westerly winds spinning in the upper atmosphere above the South Pole until they move to the surface.

The winds track northwards until they are over Australia, blowing eastwards across the dry centre to New South Wales and Queensland states, which are currently struggling through one of the driest periods on record.

"You start getting more winds from central Australia, from the desert and less winds from the ocean, so they tend to have drier, warmer conditions in New South Wales and Southern Queensland," Watkins said.

The impacts of the Antarctic event in Australia will start to arrive in the coming weeks, and be particularly felt in October before the weather pattern is expected to break down in December or January.

The east of Australia has been battling hundreds of bushfires in recent weeks, in an unusually early start to the season.

[dissident]

The claim that an SSW will control an Australian drought is downright BS. The SSW occurs well above 100 hPa where there is less than 10% of the atmospheric mass. Wind changes in the stratosphere do not just move on down to the surface and preserve their intensity. Any wind anomaly originating in the the stratosphere experiences exponential attenuation as it descends. But that is not all. The dynamical regimes of the troposphere and stratosphere are distinct. The tropospheric weather is dominated by baroclinic instability which includes blocking events. Thanks to the exponential decrease of air density with height, we have the troposphere dog waving the stratosphere tail. Events in the stratosphere are induced by tropospheric dynamics such as as quasi-stationary planetary wave fluxes originating from the land-sea pressure contrasts and wave-wave interactions for Rossby waves and baroclinic eddies.

The impact of dynamical processes in the stratosphere on the troposhere are subtle. There is a small annular surface pressure anomaly the interacts with tropospheric storm tracks and impacts the so called annular modes like the "Southern Oscillation". This process is normally not active in the southern hemisphere because the stratospheric polar vortex is too strong and stable to be disturbed by SSW events or wave-mean flow interaction in general to produce a significant surface pressure oscillation. While SSWs can influence storm track dynamics to some extent, if you are going to talk about droughts, then you have to deal with blocking dynamics. Blocks are a type of stalled baroclinic instability resonance mode. Instead of the subtropical jet spewing more eddies (low pressure systems) as is common when the baroclinicity is increased by global warming via the Hadley circulation (that induces and maintains the subtropical zonal jets), it can instead undergo a strong deviation from zonality, slow down and produce a large meridional excursion. This axially asymmetric state requires heat energy to be maintained so blocking does get worse thanks to global warming. But such blocks are not induced and maintained by any stratospheric dynamical process instead it is tropospheric wave-wave and wave-mean flow interactions that prime them. Stratospheric dynamics acts like more noise in the whole system which can randomly kick a weather state into gear. But it is silly to claim that any SSW will produce tropospheric weather. The occurence of SSWs in the southern hemisphere is just a sign that climate change is real of which there was never any doubt.

[rockdoc123]

There are two new important papers out just recently in regards to Antarctica:

Wang, Y. et al, 2019. A new 200-year spatial reconstruction of West Antarctic Surface Mass Balance. JGR Atmospheres, pp 5282-5295. https://doi.org/10.1029/2018JD029601

Abstract

High‐spatial resolution surface mass balance (SMB) over the West Antarctic Ice Sheet (WAIS) spanning 1800–2010 is reconstructed by means of ice core records combined with the outputs of the European Centre for Medium‐Range Weather Forecasts “Interim” reanalysis (ERA‐Interim) and the latest polar version of the Regional Atmospheric Climate Model (RACMO2.3p2). The reconstruction reveals a significant negative trend (−1.9 ± 2.2 Gt/year·per decade) in the SMB over the entire WAIS during the nineteenth century, but a statistically significant positive trend of 5.4 ± 2.9 Gt/year·per decade between 1900 and 2010, in contrast to insignificant WAIS SMB changes during the twentieth century reported earlier. At regional scales, the Antarctic Peninsula and western WAIS show opposite SMB trends, with different signs in the nineteenth and twentieth centuries. The annual resolution reconstruction allows us to examine the relationships between SMB and large‐scale atmospheric oscillations. Although SMB over the Antarctic Peninsula and western WAIS correlates significantly with the Southern Annular Mode due to the influence of the Amundsen Sea Low, and El Niño/Southern Oscillation during 1800–2010, the significant correlations are temporally unstable, associated with the phase of Southern Annular Mode, El Niño/Southern Oscillation and the Pacific decadal oscillation. In addition, the two climate modes seem to contribute little to variability in SMB over the whole WAIS on decadal‐centennial time scales. This new reconstruction also serves to identify unreliable precipitation trends in ERA‐Interim and thus has potential for assessing the skill of other reanalyses or climate models to capture precipitation trends and variability.

Clerc, F et al, 2019. Marine ice cliff instability mitigated by slow removal of ice shelves. Geoph Res Lett, doi: 10.1029/2019GL084183

Plain words summary:

The seaward flow of ice from grounded ice sheets to the ocean is often resisted by the buttressing effect of floating ice shelves. These ice shelves risk collapsing as the climate warms, potentially exposing tall cliff faces. Some suggest ice cliffs taller than ~90 m could collapse under their own weight, exposing taller cliffs further to the interior of a thickening ice sheet, leading to runaway ice‐sheet retreat. This model, however, is based on studies of pre‐existing cliffs found at calving fronts. In this study, we consider the transient case, examining the processes by which an ice cliff forms as a buttressing ice shelf is removed. We show that the height at which a cliff collapses increases with the timescale of ice‐shelf removal. If the ice shelf is removed rapidly, deformation may be concentrated, forming vertical cracks and potentially leading to the collapse of small (e.g., 90‐m) cliffs. However, if we consider ice‐shelf collapse timescales longer than a few days (consistent with observations), deformation is distributed throughout the cliff, which flows viscously rather than collapsing. We expect including the effects of such ice‐shelf collapse timescales in future ice‐sheet models would mitigate runaway cliff collapse and reduce predicted ice‐sheet mass loss.

Why are these two papers important? First off the Wang et al paper points to the fact that in contrast to what was previously thought the WAIS has been subject to a significant positive trend of Surface Mass Balance (snowfall – surface melt-ablation) in the 1900 – 2010 period meaning all losses have been mechanical at the ice sheet toe in that region. Interestingly that is in contrast to the picture in Antarctic Pennisula where SMB trends were overall negative. This suggests that a direct link to increasing global temperature is not relevant in terms of melt and that the actual picture is regional. With SMB increasing then you are left with arguing that ice shelf instability due to ice cliff collapse will be the cause of catastrophic failure in the future (as has been argued by at least one paper from a theoretical standpoint). The Clerc et al paper, however, rules that out as being of importance, their point being that anything that happens for more than a single day is no longer brittle failure but will be viscous flow thus mitigating runaway cliff collapse and reduce predicted ice sheet mass loss. At current rates of loss from Antarctica as a whole, the impact on sea-level rise is about 1/3 mm per year or a total of 24 mm by 2100. Taken together the two papers should alleviate much of the doom and gloom handwringing out there.

[Plantagenet]

A new study just out in NATURE COMMUNICATIONS shows that sea level rise during the last interglacial ca 125,000 years ago was largely driven by ice loss from ANTARCTICA.

nature.com/articles/s41467-019-12874-3

Many people assume that the ice in Antarctica is more or less stable....but this study demonstrates that actually Antarctica is the main source of water contributing to the final culmination of sea level rise at the peak of the last interglacial.

The key element is ice cliff instability.....at some point massive calving in Antarctica produced rapid ice loss and concomitant rapid sea level rise.

We may be approaching that point again today as our current global warming progresses.

CHEERS!

[rockdoc123]

My comments would be: nobody was around back there to ascertain what the mechanism of sea level rise was and there is zero paleo evidence for "massive calving in Antarctica" so that mechanism is pretty much speculation on your part. The paper I just pointed to in this thread:

Clerc, F et al, 2019. Marine ice cliff instability mitigated by slow removal of ice shelves. Geoph Res Lett, doi: 10.1029/2019GL084183

demonstrated that ice shelf collapse is self-limiting meaning runaway cliff collapse is unlikely.

The Rohling et al paper you point to also is talking about relative sea-level rise, not absolute sea-level rise (although they don't seem to recognize a distinction and I looked through their methodology to find no mention of isostatic adjustments). Using reefs to measure high stand and low stand is great but there is no way of telling how much is due to the sea rising and how much is due to land falling. In the case of reefs, this is pretty important because they typically subside which allows them to grow vertically, hence relative highstand would look much larger than actual highstand. This is why sequence stratigraphers tend to limit themselves to looking at relative sea level rise and fall.

[justinhinkle]

The average annual temperature ranges from about −10°C on the Antarctic coast to −60°C at the highest parts of the interior.

[Plantagenet]

The average annual temperature ranges from about −10°C on the Antarctic coast to −60°C at the highest parts of the interior.

The key area is along the coasts. Already several of the huge ice shelves along the Antarctic Peninsula have disintegrated and the remaining ones will probably go to pieces soon. Ice shelves are temperature sensitive, and warming is progressing on the Antarctic Peninsula quite rapidly.



When I was in Antarctica earlier this year one of the most dramatic things I saw were huge tabular ice bergs that break off from ice shelves.....their size was awe inspiring.

Cheers!

[Newfie]

The average annual temperature ranges from about −10°C on the Antarctic coast to −60°C at the highest parts of the interior.

I missed your first post. Thanks for the info and welcome aboard.

[Newfie]

Arctic but I think part of a similar process.

[dohboi]

the increasing frequency of atmospheric river events poses a threat to WAIS stability with continued global warming (see the linked reference):

Jonathan D. Wille et al. (2019),

West Antarctic surface melt triggered by atmospheric rivers

Nature Geoscience 12, 911–916, doi:10.1038/s41561-019-0460-1

https://www.nature.com/articles/s41561-019-0460-1

Abstract: "Recent major melting events in West Antarctica have raised concerns about a potential hydrofracturing and ice shelf instability. These events often share common forcings of surface melt-like anomalous radiative fluxes, turbulent heat fluxes and föhn winds. Using an atmospheric river detection algorithm developed for Antarctica together with surface melt datasets, we produced a climatology of atmospheric river-related surface melting around Antarctica and show that atmospheric rivers are associated with a large percentage of these surface melt events. Despite their rarity (around 12 events per year in West Antarctica), atmospheric rivers are associated with around 40% of the total summer meltwater generated across the Ross Ice Shelf to nearly 100% in the higher elevation Marie Byrd Land and 40–80% of the total winter meltwater generated on the Wilkins, Bach, George IV and Larsen B and C ice shelves. These events were all related to high-pressure blocking ridges that directed anomalous poleward moisture transport towards the continent. Major melt events in the West Antarctic Ice Sheet only occur about a couple times per decade, but a 1–2 °C warming and continued increase in atmospheric river activity could increase the melt frequency with consequences for ice shelf stability."

(Thanks to aslr at asif for text and link)

[Tanada]

To be honest I am a little surprised that Larsen C has held on this long. However if you look at both sides of the Antarctic Peninsula you will see the pattern that has developed is Larsen A in 1997, then Larsen B in 2002, then Wilkins in 2008-2009 on the other side of the peninsula, that leaves Larsen C and George VI (next to the former Wilkins) as the only remaining major ice shelves on the peninsula.