Support the Arctic Sea Ice Forum and Blog

Author Topic: ENSO general science  (Read 2185 times)

gerontocrat

  • Multi-year ice
  • Posts: 20880
    • View Profile
  • Liked: 5313
  • Likes Given: 69
ENSO general science
« on: August 04, 2023, 06:05:44 PM »
We need a thread to discuss future trends in the ENSO cycle

e,g, this new paper,,,

https://www.nature.com/articles/s41586-023-06236-9
Increased occurrences of consecutive La Niña events under global warming

Abstract
Most El Niño events occur sporadically and peak in a single winter1,2,3, whereas La Niña tends to develop after an El Niño and last for two years or longer4,5,6,7. Relative to single-year La Niña, consecutive La Niña features meridionally broader easterly winds and hence a slower heat recharge of the equatorial Pacific6,7, enabling the cold anomalies to persist, exerting prolonged impacts on global climate, ecosystems and agriculture8,9,10,11,12,13.

Future changes to multi-year-long La Niña events remain unknown. Here, using climate models under future greenhouse-gas forcings14, we find an increased frequency of consecutive La Niña ranging from 19 ± 11% in a low-emission scenario to 33 ± 13% in a high-emission scenario, supported by an inter-model consensus stronger in higher-emission scenarios. Under greenhouse warming, a mean-state warming maximum in the subtropical northeastern Pacific enhances the regional thermodynamic response to perturbations, generating anomalous easterlies that are further northward than in the twentieth century in response to El Niño warm anomalies. The sensitivity of the northward-broadened anomaly pattern is further increased by a warming maximum in the equatorial eastern Pacific. The slower heat recharge associated with the northward-broadened easterly anomalies facilitates the cold anomalies of the first-year La Niña to persist into a second-year La Niña. Thus, climate extremes as seen during historical consecutive La Niña episodes probably occur more frequently in the twenty-first century.

Observed features and model selection


a, Skewness of historical (1900–1999) Niño3.4 SST anomaly in observation (black bar) and CMIP6 models (coloured bars). The vertical line separates selected models with positive skewness (orange bars) from non-selected models with negative skewness (blue bars). The error bar denotes 1.0 s.d. of the inter-model spread in the selected (non-selected) MME.

b, Temporal evolution of Niño3.4 SST anomaly composited for multi-year (red) and single-year (blue) La Niña events in the selected models over 1900–1999. Solid lines and shading indicate multi-model mean and 1.0 s.d. of a total of 10,000 inter-realizations based on a bootstrap method, respectively. Dashed lines indicate observations. The time series are smoothed with a three-month running-mean filter before analysis. The vertical grey shading denotes the time (October to February) when ENSO typically matures.

c,d, Multi-model mean composite map of anomalous SST (°C; colouring) and surface wind stress (N m−2; vectors) for single-year (c) and multi-year (d) La Niña events during D(1)JF(2) in 1900–1999. Shown are values at which the ensemble mean exceeds 1.0 s.d. of the inter-model spread using a bootstrap method. Selected models simulate reasonably the observed evolution and pattern of multi-year La Niña.

Fig. 2: Projected increase in frequency of multi-year La Niña events.

a, Comparison of multi-year La Niña numbers (events per 100 years) over 1900–1999 (blue bars) and 2000–2099 (red bars) in the selected models under SSP585 (left of the vertical line). Multi-model mean results from other emission scenarios are also provided for the selected ensembles. Models that simulate a decrease are greyed out. Shown in the last four columns are the MME results of non-selected models under SSP585 and of selected models under low-emission scenarios. Note that not exactly the same set of models is used under different scenarios owing to data unavailability. The horizontal dashed line indicates observation.

b, Evolution of multi-year La Niña occurrence (events per 100 years) diagnosed in a 60-year sliding window that moves separately in the past 500 years of piControl (black) and from 1850 (the start of historical run; blue) to the end of the twenty-first century under SSP585 (red). Years on the x axis denote the end year of the sliding window. Solid lines and shading indicate multi-model mean and 95% confidence intervals based on a Poisson distribution, respectively. The dashed black line indicates the mean level of piControl.

c, As in a but for proportions (as a percentage) of multi-year La Niña occurrences in different situations under SSP585 (see letters on the x axis and corresponding descriptions at the bottom). Error bars on the multi-model mean in a and c are calculated as 1.0 s.d. of 10,000 inter-realizations of a bootstrap method. Disproportionally more frequent multi-year La Niña events occur after a strong El Niño during the 2000–2099 period than during the 1900–1999 period.

Summary and discussion
Our finding of an increase in the occurrence of consecutive La Niña events under greenhouse warming is underpinned by northward-broadened easterly anomalies in the subtropical North Pacific in response to equatorial eastern Pacific warm anomalies. The northward broadening and its increased occurrences are—in turn—a consequence of a faster mean-state warming in the subtropical northeastern Pacific that induces a further northern and more sensitive response to El Niño convective anomalies, which are—per se—intensified by a faster warming in the equatorial eastern Pacific. The consequence of the northward-broadened easterlies is a slower heat recharge of the equatorial Pacific, leaving a colder upper-ocean condition after the first-year La Niña to persist into the second year. Our discovery of a two-way interaction between the tropics and subtropics that intensifies under greenhouse warming represents an advance beyond recent findings of a one-way warming-induced enhancement of the NPMM influence on ENSO50,51. Our result of a probable future increase in multi-year La Niña frequency strengthens calls for an urgent need to reduce greenhouse-gas emissions to alleviate the adverse impacts.
« Last Edit: August 04, 2023, 06:13:17 PM by gerontocrat »
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

kassy

  • Moderator
  • First-year ice
  • Posts: 8499
    • View Profile
  • Liked: 2061
  • Likes Given: 1997
ENSO general science
« Reply #1 on: August 04, 2023, 06:28:11 PM »
We could do with an ENSO general science thread. For looking at the future and also patterns from the past or whatever science will come up with.

Discussions of the current 2023 season go here:
https://forum.arctic-sea-ice.net/index.php/topic,3910.0.html
« Last Edit: August 04, 2023, 06:33:56 PM by kassy »
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

gerontocrat

  • Multi-year ice
  • Posts: 20880
    • View Profile
  • Liked: 5313
  • Likes Given: 69
Re: ENSO general science
« Reply #2 on: August 04, 2023, 07:30:01 PM »
This paper from 2019 posits that the climate models have got very wrong the influence of rising GHG gases on the tropical Pacific Ocean. Paywalled of course.

I wonder if since then the models have been changed. My italics in the extract below

https://www.nature.com/articles/s41558-019-0505-x
Strengthening tropical Pacific zonal sea surface temperature gradient consistent with rising greenhouse gases
Quote
Abstract
As exemplified by El Niño, the tropical Pacific Ocean strongly influences regional climates and their variability worldwide1,2,3. It also regulates the rate of global temperature rise in response to rising GHGs4. The tropical Pacific Ocean response to rising GHGs impacts all of the world’s population.

State-of-the-art climate models predict that rising GHGs reduce the west-to-east warm-to-cool sea surface temperature gradient across the equatorial Pacific5. In nature, however, the gradient has strengthened in recent decades as GHG concentrations have risen sharply5. This stark discrepancy between models and observations has troubled the climate research community for two decades.

Here, by returning to the fundamental dynamics and thermodynamics of the tropical ocean–atmosphere system, and avoiding sources of model bias, we show that a parsimonious formulation of tropical Pacific dynamics yields a response that is consistent with observations and attributable to rising GHGs. We use the same dynamics to show that the erroneous warming in state-of-the-art models is a consequence of the cold bias of their equatorial cold tongues. The failure of state-of-the-art models to capture the correct response introduces critical error into their projections of climate change in the many regions sensitive to tropical Pacific sea surface temperatures.
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

vox_mundi

  • Multi-year ice
  • Posts: 10389
    • View Profile
  • Liked: 3528
  • Likes Given: 761
Re: ENSO general science
« Reply #3 on: September 05, 2023, 04:57:36 PM »
Extreme El Niño Weather Saw South America's Forest Carbon Sink Switch Off
https://phys.org/news/2023-09-extreme-el-nio-weather-south.html

Tropical forests in South America lose their ability to absorb carbon from the atmosphere when conditions become exceptionally hot and dry, according to new research.

... Research led by Dr. Amy Bennett, a Research Fellow at the University of Leeds, found that in 2015–2016, when an El Niño climate event resulted in drought and the hottest temperatures ever recorded, South American forests were unable to function as a carbon sink.

"Investigating what happened in the Amazon during this huge El Niño event gave us a window into the future by showing how unprecedented hot and dry weather impacts forests."

The researchers reported their findings in the journal Nature Climate Change. The study united the RAINFOR and PPBio research networks, with more than 100 scientists measuring forests for decades across 123 experimental plots.

The plots span Amazon and Atlantic forests as well as drier forests in tropical South America.

These direct, tree-by-tree records showed that most forests had acted as a carbon sink for most of the last 30 years, with tree growth exceeding mortality. When the 2015–2016 El Niño hit, the sink shut down. This was because tree death increased with the heat and drought.

"Here in the southeastern Amazon on the edge of the rainforest, the trees may have now switched from storing carbon to emitting it. While tree growth rates resisted the higher temperatures, tree mortality jumped when this climate extreme hit."

... Of the 123 plots studied, 119 of them experienced an average monthly temperature increase of 0.5° Celsius and 99 of the plots suffered water deficits. Where it was hotter, it was also drier.



Prior to El Niño, the researchers calculated that the plots were storing and sequestering around one third of a metric ton of carbon per hectare per year. This declined to zero with the hotter and drier El Niño conditions.

The change was due to biomass being lost through the death of trees. ... those forests more used to a drier climate at the dry periphery of the tropical forest biome turned out to be most vulnerable to drought.

This suggested some trees were already operating at the limits of tolerable conditions.

Sensitivity of South American tropical forests to an extreme climate anomaly, Nature Climate Change (2023)
https://www.nature.com/articles/s41558-023-01776-4

mpact of the 2015–2016 El Niño on the carbon dynamics of South American tropical forests, Nature Climate Change (2023)
https://www.nature.com/articles/s41558-023-01777-3
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― anonymous

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

kiwichick16

  • Grease ice
  • Posts: 995
    • View Profile
  • Liked: 94
  • Likes Given: 39
« Last Edit: September 16, 2023, 03:25:22 PM by kassy »

Rodius

  • Nilas ice
  • Posts: 2228
    • View Profile
  • Liked: 656
  • Likes Given: 46
Re: ENSO general science
« Reply #5 on: September 16, 2023, 03:05:08 AM »
Kicking in at NZ

https://www.msn.com/en-nz/news/other/el-ni%C3%B1o-incoming-nz-s-climate-to-take-rapid-turn-within-weeks/ar-AA1guehZ

Meh... if you are worried about NZ, you should move to Oz lol
(I lived in Auckland in '97/'98 and the drought at that time was really bad. We almost ran out of water that summer, within weeks if memory serves and got a lucky break in a freak storm. The rain dancers took credit for that.)
« Last Edit: September 16, 2023, 03:25:44 PM by kassy »

kiwichick16

  • Grease ice
  • Posts: 995
    • View Profile
  • Liked: 94
  • Likes Given: 39
Re: ENSO general science
« Reply #6 on: September 17, 2023, 02:14:50 AM »
@  rodius   ...each countries systems are set up for their own normal ...... of course we are all heading towards abnormal

kassy

  • Moderator
  • First-year ice
  • Posts: 8499
    • View Profile
  • Liked: 2061
  • Likes Given: 1997
Re: ENSO general science
« Reply #7 on: December 07, 2023, 02:24:20 PM »
What Do We Know About El Niño? Maybe Less Than We Thought

...

Unfortunately, our knowledge of this weather pattern has always been spotty at best: we can’t predict it very far in advance, because it doesn’t follow a set schedule; we don’t know exactly what causes it; and every time it happens, it’s different from before. In short, the entire planet is kind of at the mercy of this “little boy.”

But wait! It gets worse – because according to a couple of papers from researchers out of Innsbruck, Austria, this year, we may actually know even less than we thought.

What is El Niño?
You’ve likely heard of El Niño before, but understanding the interactions that underlie it – and, therefore, how our knowledge has changed thanks to these new studies – is a little more complex.

For one thing, it’s only half of the picture, meteorologically speaking. “El Niño and La Niña are two phases of the naturally occurring climate phenomenon called the El Niño–Southern Oscillation (ENSO),” explains Imperial College London’s Grantham Institute.

“[The ENSO] leads to the most dramatic year-to-year variation of Earth’s climate,” it continues. “El Niño is characterised by warmer global temperatures, while La Niña years are typically cooler.”

When and why either of these weather patterns occur is kind of a mystery, even today. We know El Niño is more frequent than La Niña, generally speaking, and both tend to last for nine to 12 months on average – but neither event happens on a regular schedule. The best we can say is that they turn up every two to seven years or so.

“During normal conditions in the Pacific Ocean, trade winds blow west along the equator, taking warm water from South America towards Asia,” explains the National Ocean and Atmospheric Administration (NOAA) factsheet on the phenomenon. “To replace that warm water, cold water rises from the depths – a process called upwelling.”

But “El Niño and La Niña are two opposing climate patterns that break these normal conditions,” the agency continues. During El Niño, the Pacific winds weaken, reducing that upwelling of cold water in the East and pushing warmer tides towards the west coast of the Americas; sea surface temperatures can rise by up to 4°C (7°F) across the Pacific, and atmospheric circulation patterns can be affected on a global scale.

“El Niño causes many changes in weather patterns across the globe,” said Auroop Ganguly, co-director of Northeastern's Global Resilience Institute, in a statement this October.

“It has been called the ‘seesaw’ effect,” he added: the phenomenon often brings more frequent and intense storms over the west coasts of North and South America, while causing droughts in Africa and South Asia.

What drives El Niño?
We may not know precisely what sets off an El Niño event, but scientists have had suspicions for a while as to what may govern the patterns of these boisterous weather phenomena. One of those ideas – the so-called “bipolar seesaw mechanism” – is pretty well-accepted; the other – a link with the sun’s magnetic cycle – is less so. Guess which one the new research supports?

“Our findings… [challenge] the bipolar seesaw hypothesis,” notes one of the new papers, published in The Innovation Geoscience. “While the bipolar seesaw hypothesis is well-supported for the Atlantic sector, its relevance for worldwide millennial-scale climate change remains uncertain.”

The question that the hypothesis is aimed at answering is the cause of climate change on the millennium scale – something that has been “a long-standing challenge in paleoclimate science,” the researchers note. Put as simply as possible, it suggests that it’s changes in the Atlantic Meridional Overturning Circulation, or AMOC – a large system of ocean currents that carry warm water from the tropics into the North Atlantic – which govern climatic shifts in the Southern hemisphere.

“This concept postulates that an AMOC collapse would block northward heat flow, with heat left to accumulate in the Southern Hemisphere,” explain the researchers. “As AMOC stabilizes, northward flow would resume, causing cooling in the Southern Hemisphere.”

But if the hypothesis is correct, the team write, then we should expect climate records from the Pacific to line up with those from the Atlantic. And it turns out, they’re not.

How do they know? Luckily, we have a very good record of the climate history of the Atlantic, in the form of Greenland ice cores. They’re “one of the best tools to reconstruct the climate prior to the instrumental era,” according to Liz Thomas, head of the ice cores team at British Antarctic Survey, providing information on everything from the particular makeup of the atmosphere throughout the millennia to evidence of massive ancient solar storms.

But finding a record of the same history in the Pacific has proven a little more tricky – which is why, instead of ice, the researchers looked to cave deposits known as speleothems for their information.

“We report an independently dated high-latitude speleothem proxy record from Alaska, which provides valuable insights into the North Pacific climate,” the paper reports. “Our findings reveal that this speleothem record is not in-sync with the Greenland ice-core record… [but] aligns with the tropical Pacific [record].”

So, if it’s not a planetary playground apparatus that’s to blame for the millennia of ENSO cycles, then what is it?

The Walker switch
It’s here that we find the Austrian team’s first big result: the existence of what they’ve termed the “Walker switch.”

Named for the Walker circulation – ENSO’s “atmospheric buddy,” according to meteorologist Tom Di Liberto – the proposed Walker switch mechanism puts the blame for ENSO events on two separate, yet intertwined, phenomena. The first is the so-called “ocean thermostat” mechanism: it “infers that if there is heating over the entire tropics, then the Pacific will warm more in the west than the east because strong upwelling and surface divergence in the east moves some of the heat poleward,” the researchers explain.

“Therefore, the east-west temperature gradient will strengthen, causing easterly winds to intensify, further enhancing the zonal temperature gradient,” they write. “This process leads to a La Niña-like mean state in response to increased solar forcing.”

But there were times, the team found, when the climate record didn’t quite match up with what they would expect, if that was all that was going on. Instead, they suggest, this thermostatic relationship might be weakened once a certain threshold gets passed: too much radiation from the sun, they posit, and the surface temperatures even out across the ocean enough for the Walker circulation to become more influential than the thermostat mechanism.

“The ‘Walker switch’ concept helps us better explain the complex interplay of factors that have shaped climate dynamics” in the equatorial Pacific and northern latitudes, said Paul Wilcox, a researcher in the Department of Geology at the University of Innsbruck and co-author of both studies, in a statement.

Of course, it’s only a hypothesis. “We acknowledge that this conceptual mechanism is currently difficult to fully prove,” the authors admit.

“Nevertheless,” they say, “based on the existing evidence, it offers a feasible solution to several climate enigmas.”

Radiation from the sun? Is that what you were talking about before?
Not exactly. See, all that Walker switch stuff was about explaining El Niño on a millennia-long scale – but when it comes to shorter-term patterns, there’s something altogether more sci-fi going on.

A few years ago, a team of scientists from the University of Maryland and the National Center for Atmospheric Research made a controversial suggestion: that ENSO patterns were linked to the sun’s magnetic cycle. While the exact mechanism was – and still is – hazy, their evidence did seem to show that a switch between El Niño and La Niña tends to be aligned with what’s known as “terminator events” in the solar cycle (it sounds worse than it is – it’s basically just the Sun’s New Year).

“We are not the first scientists to study how solar variability may drive changes to the Earth system,” said Bob Leamon, an Associate Research Scientist at the University of Maryland and co-author of the paper that proposed the link back in 2021. “But we are the first to apply the 22-year solar clock. The result – five consecutive terminators lining up with a switch in the El Niño oscillation – is not likely to be a coincidence.”

At first, many other climate scientists were skeptical. “I wouldn’t go so far as to call the results of this work a ‘conclusion’ per se,” space weather physicist Tamitha Skov told Washington Post at the time; “rather something akin to a steppingstone in a new direction.”

But the second paper from the team at Innsbruck, which was published in the journal Geophysical Research Letters in October, seems to support the hypothesis – at least, to a point. By analyzing speleothems in southeastern Alaska, the researchers were able to deduce a record of the influence of solar radiation on the local climate – and, indeed, they write, “ENSO was significantly influenced by solar irradiance over the past ∼3,500 years.”

But very, very recently – only about 50 years ago – that relationship started to break down. And the reason? You guessed it: our old friend climate change.

“ENSO [is] now being dominated by anthropogenic forcing,” the authors write. “This implies a new ENSO mean state that will need to be incorporated into future climate projections.”

...

https://www.iflscience.com/what-do-we-know-about-el-nino-maybe-less-than-we-thought-71868
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

vox_mundi

  • Multi-year ice
  • Posts: 10389
    • View Profile
  • Liked: 3528
  • Likes Given: 761
Re: ENSO general science
« Reply #8 on: March 20, 2024, 03:50:23 PM »
Counteracting Effects on ENSO Due to Ocean Chlorophyll Interannual Variability and Instability In the Tropical Pacific
https://phys.org/news/2024-03-counteracting-effects-enso-due-ocean.html



In as study published in the journal Science China Earth Sciences and led by Prof. Rong-Hua Zhang (School of Marine Sciences, Nanjing University of Information Science and Technology), large perturbations in chlorophyll (Chl) were observed to coexist at interannual and tropical instability wave (TIW) scales in the tropical Pacific.

"At present, their combined effects on El Niño-Southern Oscillation (ENSO) through ocean biology-induced heating (OBH) feedbacks are not understood well," Zhang says.

Zhang and his coworkers adopted a hybrid coupled model (HCM) for the atmosphere and ocean physics-biogeochemistry (AOPB) in the tropical Pacific to quantify how Chl perturbations can modulate ENSO at interannual and TIW scales, individually or collectively, respectively.

The team found that the HCM-based sensitivity experiments demonstrate a counteracting effect on ENSO: the bio-climate feedback due to large-scale Chl interannual variability acts to damp ENSO through its impact on upper-ocean stratification and vertical mixing, whereas that due to TIW-scale Chl perturbations tends to amplify ENSO.

The researchers also illustrated that because ENSO simulations are sensitively dependent on the ways Chl effects are represented at these different scales, it is necessary to adequately take into account these related differential Chl effects in climate modeling. A bias source for ENSO simulations is illustrated that is related to the Chl effects in the tropical Pacific, adding new insight into interactions between the climate system and ocean ecosystem on different scales in the region.

"These new exciting results reveal a level of complexity of ENSO modulations resulting from Chl effects at interannual and TIW scales, which are associated with ocean biogeochemical processes and their interactions with physical processes in the tropical Pacific," Zhang says.

Rong-Hua Zhang et al, Counteracting effects on ENSO induced by ocean chlorophyll interannual variability and tropical instability wave-scale perturbations in the tropical Pacific, Science China Earth Sciences (2023)
https://link.springer.com/article/10.1007/s11430-023-1217-8
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― anonymous

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

vox_mundi

  • Multi-year ice
  • Posts: 10389
    • View Profile
  • Liked: 3528
  • Likes Given: 761
Re: ENSO general science
« Reply #9 on: April 01, 2024, 04:09:05 PM »
Atmospheric Scientists Link Arctic Sea Loss Ice to Strong El Niño Events
https://phys.org/news/2024-04-atmospheric-scientists-link-arctic-sea.html



A new study, published in Science Advances by researchers at the University at Albany and Nanjing University of Information Science and Technology in China, has found that these events, which typically occur once every few years, might become even stronger due to melting Arctic sea ice.

Using a combination of climate model simulations and observational data, the researchers found that the current interaction of Arctic sea ice with the atmosphere reduces the strength of El Niño events by up to 17%, compared to when the interaction is removed.

"Climate models are already projecting a strengthened El Niño in the upcoming decades due to global warming. Arctic sea ice is also projected to decline rapidly in the upcoming decades," said Aiguo Dai, a Distinguished Professor at UAlbany's Department of Atmospheric and Environmental Sciences and study co-author.

"Our new study suggests that Arctic sea ice-air interactions in the current climate significantly reduce the amplitude of El Niño–Southern Oscillation, compared to the case without such interactions. This represents a new example of the various impacts of Arctic sea ice on our climate."

Jiechun Deng et al, Arctic sea ice–air interactions weaken El Niño–Southern Oscillation, Science Advances (2024).
https://www.science.org/doi/10.1126/sciadv.adk3990
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― anonymous

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

vox_mundi

  • Multi-year ice
  • Posts: 10389
    • View Profile
  • Liked: 3528
  • Likes Given: 761
Re: ENSO general science
« Reply #10 on: April 09, 2024, 09:40:59 PM »
Heat from El Niño Can Warm Oceans Off West Antarctica—and Melt Floating Ice Shelves from Below
https://phys.org/news/2024-04-el-nio-oceans-west-antarctica.html



Antarctic ice shelves are now losing an alarming 150 billion tons of ice per year, adding more water to the ocean and accelerating global sea level rise by 0.6 mm per year. Ice shelves in West Antarctica are particularly prone to melting from the ocean, as many are close to water masses above 0°C.

While the melting trend is clear and concerning, the amount can vary substantially from year-to-year due to the impact of both natural climate fluctuations and human-made climate change. To figure out what is going on and to prepare for the future, we need to tease apart the different drivers—especially El Niño-Southern Oscillation, the world's largest year-to-year natural climate driver.

Our new research, published in Geophysical Research Letters, explores how heat brought by El Niño can warm the ocean around West Antarctica and increase melting of the ice shelves from below.



Using satellite data, researchers recently found that West Antarctic ice shelves actually gain height but lose mass during El Niño. That's because more low-density snow falls at the top of the ice shelves, while at the same time more warm water flows under the ice shelves where it melts compressed high-density ice from underneath.

... The energy brought by El Niño's atmospheric waves to West Antarctica weakens the prevailing easterly winds along the coasts.

Normally, most of the warm water reservoir is located off the continental shelf rather than on the continental shelf. As the winds weaken, more of this warmer water—known as Circumpolar Deep Water—is able to flow onto the continental shelf and near the base of the floating ice shelves.

During La Niña, the opposite occurs and the ice rebounds. Winds along the coast strengthen, pushing more cold surface water onto the continental shelf and preventing warm water from flowing under the ice shelves.

Researchers have found El Niño and La Niña have already become more frequent and more extreme.

If this trend continues, as climate projections suggest, we can expect warming around West Antarctica to get even stronger during El Niño events, accelerating ice shelf melting and speeding up sea level rise.

More frequent and stronger El Niño events could also push us closer to a tipping point in the West Antarctic ice sheet, after which accelerated melting and mass loss could become self-perpetuating. That means the ice wouldn't melt and reform but begin to steadily melt.

Maurice F. Huguenin et al, Subsurface Warming of the West Antarctic Continental Shelf Linked to El Niño‐Southern Oscillation, Geophysical Research Letters (2024).
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL104518
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― anonymous

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

gerontocrat

  • Multi-year ice
  • Posts: 20880
    • View Profile
  • Liked: 5313
  • Likes Given: 69
Re: ENSO general science
« Reply #11 on: April 09, 2024, 09:57:16 PM »
The attached graphs + map of the Antarctic Drainage Basins shows how nearly all the AIS Mass Loss is in West Antarctica, and mostly in just 3 coastal basins, (basins 20, 21 & 22).
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)