Ice Apocalypse - Multiple Meters Sea Level Rise

[kassy]

Ah yes but that is the total from the WAIS. That will take while plus it´s the first meter(s) that already finishes of many low lying areas.

[kassy]

A hidden feedback loop under Antarctica’s glaciers could accelerate sea level rise, scientists find

Glaciers in East Antarctica could lose ice faster in the future than previously thought, scientists reported Friday, in an alarming feedback loop where glacier meltwater is triggering even more ice loss and sea level rise as the planet warms.

The findings come less than a week after scientists reported rapid melting of West Antarctica’s ice shelves may now be unavoidable, thanks to human-caused global warming. Together, these and other recent studies paint a dire picture of a melting southern continent that poses extreme risk of life-altering sea level rise around the world.

“This paper shows that it’s not only bad, but it’s even worse than we thought,” said Jamin Greenbaum, co-author of the study and assistant research geophysicist at the University of California San Diego’s Scripps Institution of Oceanography.

The study, published Friday in the journal Science Advances, focused on the Denman and Scott glaciers in East Antarctica that together hold enough ice to trigger roughly five feet of sea level rise.

Previous studies have shown that as glaciers melt, the water flows underneath them and out to sea – a process that enhances glacial melting and ice loss. Friday’s study factored that feedback into simulations to see how much it could accelerate Antarctic melting and sea level rise.

Scientists found the glaciers could retreat past a critical threshold about 25 years earlier than they would have without the meltwater discharge, if the world burns planet-warming fossil fuel at an accelerated rate.

Adding the meltwater feedback increased the sea level rise from the Denman and Scott glaciers by nearly 16% by the end of 2300 under this scenario of high levels of planet-heating pollution.

Importantly, Greenbaum said, the extra ice loss from meltwater discharge is currently excluded from climate models projecting sea level rise, despite the fact that it could be a major driver of ice loss across the whole continent. Measuring this phenomenon and accounting for it in climate models is necessary “to get a realistic picture of global sea level rise,” Greenbaum said.

...

https://edition.cnn.com/2023/10/27/world/antarctica-glaciers-meltwater-climate/index.html

Subglacial discharge accelerates future retreat of Denman and Scott Glaciers, East Antarctica
https://www.science.org/doi/10.1126/sciadv.adi9014

[kassy]

An Extreme Weather Event in 2014-2016 Sped Up Sea-Level Rise, Study Finds

In the two years between June 2014 and May 2016, world leaders came together and adopted the landmark Paris Agreement, and the global average sea level rose by a staggering 15 millimeters or 0.6 inches.

Although that rise isn't much more than the length of a fingernail, it was actually a frightening leap on long-term trends that a new study suggests was driven by a particularly extreme and unusual climate period.

Global average sea levels have risen by over 9 centimeters (about 3.5 inches) since 1993, the first year that NASA satellites were whizzing around our planet monitoring changes in sea levels.

From those long-term datasets, scientists estimated global mean sea levels should rise about 4 millimeters per year over the 2014-2016 period – yet global sea levels rose, on average, nearly twice as much as expected in that time: 15 millimeters instead of the expected 8 (0.3 inches).

A new study from a team of oceanographers at the French National Centre for Scientific Research (CNRS) has linked that sudden jump to back-to-back El Niño events in the Pacific Ocean, which appears to have sped up sea-level rise by shifting rainfall patterns and drying out the Amazon Basin.

El Niño is one phase of the El Niño Southern Oscillation (ENSO), an irregular shift in wind patterns and sea surface temperatures that swings back and forth across the tropical Pacific Ocean. The change in trade winds pushes warm water either towards the west coast of the Americas (as so happens in El Niño) or towards Asia (in La Niña, the opposite phase).

Two consecutive El Niño events in 2014-2015 and 2015-2016 coincided with the 15-millimeter rise in global mean sea levels. The 2015-2016 El Niño event was particularly extreme, with 2016 quickly surpassing 2015 as the hottest year on record, according to the World Meteorological Organization (WMO).

"Those unusual El Niño events affected the precipitation pattern worldwide, decreasing the terrestrial water storage in the Amazon basin and therefore leading to an increase of the global mean ocean mass," William Llovel and colleagues explain in their paper.

To come to this finding, the researchers combined data from multiple satellites and a global array of floating ocean sensors, and analyzed the changes in ocean temperatures, ocean mass, and the amount of water stored on land, in river systems like the Amazon Basin.

The Amazon Basin covers about 35 percent of the South American continent, a huge water catchment consisting of the Amazon River and its capillary-like tributaries.

Llovel and colleagues found that 80 percent of the 15-millimeter rise in 2014-2016 was due to the world's oceans increasing in mass as El Niño changed rainfall patterns: the Amazon Basin held less water, and more rain fell over the eastern tropical Pacific Ocean and Argentina.

Ice sheets melting and other land water changes were also a factor, but the drying out Amazon Basin alone contributed 5 millimeters to rising seas during this period.

The remaining 20 percent or 3 millimeters of the 2014-2016 rise was attributed to the expansion of the ocean as it warmed up, the analysis showed.

No two El Niño events are the same. So investigating the imprint of past El Niño – and La Niña – events on global sea levels will help refine climate model projections of future sea-level rise, particularly in the next few decades, the researchers say.

Earlier this year, in July, the WMO declared El Niño conditions had developed in the tropical Pacific straight off the back of a 'triple-dip' La Niña which began in 2020. Extra hot temperatures are expected to follow.

https://www.sciencealert.com/an-extreme-weather-event-in-2014-2016-sped-up-sea-level-rise-study-finds

Cause of Substantial Global Mean Sea Level Rise Over 2014–2016
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL104709

[AbruptSLR]

At least someone is taking the risk of the abrupt near term collapse of the Thwaites Glacier seriously:

Keefer, B.; Wolovick, M. and Moore, J. “Feasibility of ice sheet conservation using seabed anchored curtains”, PNAS Nexus, Volume 2, Issue 3, March 2023, pgad053, https://doi.org/10.1093/pnasnexus/pgad053

https://academic.oup.com/pnasnexus/article/2/3/pgad053/7089571?login=false

Abstract
“Sea level rise is expected to be rapid and extremely damaging to coastal communities and infrastructure, with unavoidable losses and coastal protection costs in the tens of billions per year. Retreat of the Thwaites and Pine Island Glaciers is likely already in an unstable regime as their oceanic fronts are ablated by deep intruding layers of relatively warm seawater. Warm water can be blocked from reaching the grounding line by thin flexible buoyant curtains anchored to the seabed. The consequent reduction in ice shelf melting could result in increased ice sheet buttressing as the shelf makes contact with seabed highs. Flexible curtains are less costly than solid artificial barriers, more robust against iceberg collisions, and easier to repair or remove in the event of unforeseen side effects. We illustrate the technical viability of this approach by considering curtain design concepts that should withstand oceanographic forces, and feasible methods of installation. Suitable materials are commonly available. Installation of a seabed curtain in temperate ocean waters would be entirely within the capabilities of existing offshore and deep ocean construction techniques. Installing in polar waters presents severe challenges from icebergs, harsh weather, and brief working seasons, which can however, be overcome with present-day technology. An 80 km long curtain installed in 600 m deep waters on alluvial sediments could help stabilize Pine Island and Thwaites glaciers over the next few centuries at much lower cost ($40–80 billion + $1–2 billion/yr maintenance) than the global coastline protection (∼$40 billion/yr) needed due to their collapse.”

&

Article Title: “New publication: Seabed anchored curtains to prevent the collapse of West Antarctica Ice Sheet”, 29.3.2023

Abstract: “As the climate changes, more and more warm seawater reaches the glaciers of Antarctica and threatens them to collapse. A group of researchers explores how feasible the idea is to block channels that bring warm water to the glaciers with flexible buoyant curtains, anchored to the seabed. Their study has now been published in the open access journal PNAS Nexus.”

https://www.ulapland.fi/news/New-publication-Seabed-anchored-curtains-to-prevent-the-collapse-of-West-Antarctica-Ice-Sheet/38394/e0f298d6-d1df-473e-81a8-ee55d0f16aed

Extract: “The possible collapse of the West Antarctic Ice Sheet is one of the most dramatic impacts of climate warming. Currently, floating ice shelves hold the ice sheet in place. But the Thwaites and Pine Island Glaciers in Antarctica are rapidly thinning and retreating as deep salty seawater warmed by climate change licks at the undersides of their leading edges.
…
The curtains would be around 100 meters high, deployed as many in narrow sections, so that they block the stream in the lower layer but allow the outflow of nutrient-rich waters from the glaciers. Additionally, the curtains need to be flexible so that icebergs push them aside as they move past, rather than destroy them.

With warm water access reduced, the ice would thicken and reground on the seafloor to securely support the vulnerable parts of the West Antarctica ice sheet. The authors estimate that the installation of these curtains would cost 40 to 80 billion dollars and requires one to two billion dollars per year in maintenance."

[vox_mundi]

Ice Cores Provide First Documentation of Rapid Antarctic Ice Loss In the Past
https://phys.org/news/2024-02-ice-cores-documentation-rapid-antarctic.html



Researchers from the University of Cambridge and the British Antarctic Survey have uncovered the first direct evidence that the West Antarctic Ice Sheet shrunk suddenly and dramatically at the end of the Last Ice Age, around eight thousand years ago.

The evidence contained within an ice core shows that in one location, the ice sheet thinned by 450 meters—that's more than the height of the Empire State Building—in just under 200 years.

This is the first evidence anywhere in Antarctica for such a fast ice loss. Scientists are worried that today's rising temperatures might destabilize parts of the West Antarctic Ice Sheet in the future, potentially passing a tipping point and inducing a runaway collapse. The new study, published in Nature Geoscience, sheds light on how quickly Antarctic ice could melt if temperatures continue to soar.

The Antarctic ice sheets, from west to east, contain enough freshwater to raise global sea levels by around 57 meters. The West Antarctic Ice Sheet is considered particularly vulnerable because much of it sits on bedrock that lies below sea level.

Model predictions suggest that a large part of the West Antarctic Ice Sheet could disappear in the next few centuries, causing sea levels to rise. Exactly when and how quickly the ice could be lost is, however, uncertain.

... The researchers drilled a 651-meter-long ice core from Skytrain Ice Rise in 2019. This mound of ice sits at the edge of the ice sheet, near the point where grounded ice flows into the floating Ronne Ice Shelf.

After transporting the ice cores back to Cambridge at -20oC, the researchers analyzed them to reconstruct the ice thickness. First, they measured stable water isotopes, which indicate the temperature at the time the snow fell. Temperature decreases at higher altitudes (think of cold mountain air), so they were able to equate warmer temperatures with lower-lying, thinner ice.

They also measured the pressure of air bubbles trapped in the ice. Like temperature, air pressure also varies systematically with elevation. Lower-lying, thinner ice contains higher-pressure air bubbles.

These measurements told them that ice thinned rapidly 8,000 years ago. "Once the ice thinned, it shrunk really fast," said Wolff, "this was clearly a tipping point—a runaway process."



They think this thinning was probably triggered by warm water getting underneath the edge of the West Antarctic Ice Sheet, which normally sits on bedrock. This likely untethered a section of the ice from bedrock, allowing it to float suddenly and forming what is now the Ronne Ice Shelf. This then allowed neighboring Skytrain Ice Rise, no longer restrained by grounded ice, to thin rapidly.

The researchers also found that the sodium content of the ice (originating from salt in sea spray) increased about 300 years after the ice thinned. This told them that, after the ice thinned, the ice shelf shrunk back so that the sea was hundreds of kilometers nearer to their site.

Eric Wolff et al, Abrupt Holocene ice loss due to thinning and ungrounding in the Weddell Sea Embayment, Nature Geoscience (2024)
https://www.nature.com/articles/s41561-024-01375-8

Abstract

The extent of grounded ice and buttressing by the Ronne Ice Shelf, which provides resistance to the outflow of ice streams, moderate West Antarctic Ice Sheet stability. During the Last Glacial Maximum, the ice sheet advanced and was grounded near the Weddell Sea continental shelf break. The timing of subsequent ice sheet retreat and the relative roles of ice shelf buttressing and grounding line changes remain unresolved. Here we use an ice core record from grounded ice at Skytrain Ice Rise to constrain the timing and speed of early Holocene ice sheet retreat. Measured δ18O and total air content suggest that the surface elevation of Skytrain Ice Rise decreased by about 450 m between 8.2 and 8.0 kyr before 1950 ce (±0.13 kyr). We attribute this elevation change to dynamic thinning due to flow changes induced by the ungrounding of ice in the area. Ice core sodium concentrations suggest that the ice front of this ungrounded ice shelf then retreated about 270 km (±30 km) from 7.7 to 7.3 kyr before 1950 ce. These centennial-scale changes demonstrate how quickly ice mass can be lost from the West Antarctic Ice Sheet due to changes in grounded ice without extensive ice shelf calving. Our findings both support and temporally constrain ice sheet models that exhibit rapid ice loss in the Weddell Sea sector in the early Holocene.

... This study shows that SIR can become unstable without extensive simultaneous ice shelf calving. Instability could instead have been driven by ice sheet thinning and ungrounding. This possibility is well aligned with Gudmundsson et al. (2019)8, which demonstrated, using a process-based model, that ice shelf thinning drives modern grounded ice mass loss. The subsequent ice shelf calving exhibited in the record also demonstrates that calving does not necessarily result in ice sheet instability in the WSE, at least as far inland as SIR. This idea of passive ice shelf calving was proposed in Furst et al. (2016)7. The retreat of the ice shelf edge was, however, coincident with abrupt thinning close to the ice shelf margin, at least at the Lassiter Coast9. This ice shelf weakening related to nearby rapid thinning on land is proposed in cosmogenic nuclide studies

Our results are also a direct demonstration of the speed at which ice mass can be lost when the grounding line of a marine-based ice sheet retreats. Our results suggest that the elevation at SIR reduced by an average of more than 2 m per year for two centuries.

[kiwichick16]

@  abruptSLR    ......did i get my physics wrong  ......or does warm water not rise ?

[squilliam]

@  abruptSLR    ......did i get my physics wrong  ......or does warm water not rise ?

It depends on the density of the water, which is a factor of both the temperature and the salinity. Warmer waters can be denser because of higher salinity. Whilst water itself is densest at 4 degrees C, the biggest factor in the density is the salt content which is mediated by evaporation and warm water is usually saltier than colder water.

[kassy]

Global average sea level rose by about 0.3 inches (0.76 centimeters) from 2022 to 2023, a relatively large jump due mostly to a warming climate and the development of a strong El Niño.

...

The data shows that global average sea level has risen a total of about 4 inches (9.4 centimeters) since 1993. The rate of this increase has also accelerated, more than doubling from 0.07 inches (0.18 centimeters) per year in 1993 to the current rate of 0.17 inches (0.42 centimeters) per year.

"Current rates of acceleration mean that we are on track to add another 20 centimeters of global mean sea level by 2050, doubling the amount of change in the next three decades compared to the previous 100 years and increasing the frequency and impacts of floods across the world," said Nadya Vinogradova Shiffer, director for the NASA sea level change team and the ocean physics program in Washington.

https://phys.org/news/2024-03-analysis-spike-global-sea-due.html