This month’s open thread. Lots of salient stuff this month so please try and stay focused and constructive!
Reader Interactions
387 Responses to "Unforced variations: Oct 2025"
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Dave Borlace does more excellent coverage, this time on El Nino changes:
https://www.youtube.com/watch?v=QP2d4MedFPI
References (easily found in “show more” at video):
Global climate mode resonance due to rapidly intensifying El Niño-Southern Oscillation – https://www.nature.com/articles/s41467-025-64619-0
Relative Niño – a new way to measure El Niño–Southern Oscillation. Changes to the way we calculate sea surface temperatures in the tropical Pacific Ocean – https://www.bom.gov.au/news-and-media/relative-nino-a-new-way-to-measure-el-nino-southern-oscillation
Atomsk’s Sanakan @ 27 Oct 2025 said: “The most likely scenario is Killian read something on a topic like catastrophic climate change. Then Killian misrepresented that as being about human extinction. For instance:”
He may have. However there’s an alternative explanation. A few weeks ago I asked google gemini if any papers had been published claiming climate change had a 5% or similar risk of human extinction. Answer was essentially that none that gemini could find but that a 5% possibility of human extinction by 2100 is cited in some studies from a combination of ALL environmental and societal problems. I suspect Killian was confusing this with studies just related just to climate change. Sorry I didn’t keep a record of the details of the gemini response. But Killian has posted comments on wider societal and environmental problems so I can see how he might be confused.
I find myself in an unusual position partly defending this man. Because while I think climate change is a massive threat to humanity, I frequently disagree with Killians views. He’s been posting comments on this website for over 10 years. He has several times made huge dubious sounding claims about the science and mitigation. Example are that SLR is now more than exponential, and that regenerative agriculture is considerably more productive than industrial agriculture. I asked for citations and he couldn’t provide any. But he did provide copious quantities of personal abuse. I rarely respond to his comments now because its generally the same things hes said in the past.
Nigelj: “But he did provide copious quantities of personal abuse.”
I find Killian posts things that might sound controversial or extreme at first glance, but after a bit of thought, I think he is largely correct. If we carry on with BAU, I would not at all be surprised to see societal collapse on a global scale and a huge death toll as the consequences of unsustainable living and trashing the biosphere finally hit hard. He is the sort of person I would like to have a discussion with on his analyses/ideas, but the major issue with engagement is that he seems unwilling to take anything that sounds even remotely like a challenge to his assertions. It is as though his primary objective is to be right, and for everyone around him to acknowledge he is right, which puts him IMO dangerously high on the narcissisic spectrum, and if so, the only way to deal with someone like that is to disengage. It is a shame, because it is one thing to have solid theories, but if you are an asshole when engaging in discussion/debate, it doesn’t matter how right you are, you will just get people’s backs up and be ignored, the opposite of what you want, ironically.
Adam Lea @ 29 Oct 2025 at 2:30 PM, you haven’t provided any examples of where you think Killian has made big controversial claims that are “largely correct”. I can only think of one off hand – that we are at serious risk of running out of many resources.
IMHO he has definitely posted quite a large number of claims that are definitely 100% wrong. They are not even slightly correct. For example claims that global SLR is already more than exponential, and that regenerative agriculture is considerably more productive than industrial agriculture, and that scientific studies say climate change has a significant 5% probability of causing complete extinction of the human race. If he had said it could kill billions of people and cause our civilisation to collapse, I would say he’s largely correct, but he didn’t just say that he went a lot further. And all this should be pointed out to him, (or anyone else) because science is about precision and accuracy, or so I’m told.
And yes I agree with your other comments and that his communications style is self defeating.
Adam Lea says @29 Oct 2025 at 2:30 PM
Oops I made a mistake. I see that you did quote an example where you think Killian is largely correct as follows: “If we carry on with BAU, I would not at all be surprised to see societal collapse on a global scale and a huge death toll as the consequences of unsustainable living and trashing the biosphere finally hit hard”. I thought at first it was just your own view.
And he’s right about that, but IMHO some of his solutions don’t quite work. His suggestions we try to solve the problem by making very rapid and deep cuts to our use of energy, (90% within the next 2 decades ideally) and rapid cuts to industrialisation could ALSO cause societal collapse on a global scale and kill people. It could cause a massive long lasting economic depression. And quite how we persuade people to make such drastic cuts in consumption so fast eludes me.
We are caught in a bit of a trap. I think we should slowly change our system towards sustainability so the economy can adjust without a massive crash, except that the climate problem needs more urgent attention. For reasons well discussed.
Nigel: “ I find myself in an unusual position partly defending this man.. I suspect Killian was confusing some studies [of 5% risk of extinction] from a combination of ALL environmental and societal problems -with studies just related just to climate.
Don’t beat up yourself on that NIgel – that’s hardly a defense ;-) – AT BEST it would require a shocking inability to read his sources – and as result greatly distort his sources.
But that’s nothing compared to what he did afterwards – a true measure of a man is not in their victory, but in how they deal with their defeat – Killian when asked for the source of his number:
– despite declaring the multitude of sources – was unable to provide EVEN ONE
– he didn’t have the balls to admit it, quite the contrary he responded in a classic Killianian manner: with … arrogance and hutzpah:
Killian: “ Atomsk, if you do not know of the evidence, then you must keep your head very, very buried in your own delusions of certainty.
And onus of proof for this attack – Killian placed on … the person he attacked:
“ There are any number of papers and speakers/writers/tweeters discussing acceleration. I have posted the papers on the risk of extinction on these pages before. Go find them.
So the same way you “can see the world in a grain of sand”, you can see Killian, the man he is – his intellectual and ethical integrity, in this response to Atomsk.
By their posts you shall know them.
Killian read something on a topic like catastrophic climate change. He must be confused no one else possibly be confusing themselves or imagining things that don’t exist.
Killian: ” It’s not alarmist to note the worst case scenario when that scenario is 1. an existential threat and 2. a non-zero possibility. ”
Conclusion and nuance: climate scientists and interdisciplinary risk researchers increasingly warn that very bad (even CIVILISATION-ENDING) outcomes are possible and under-studied, but they typically
(a) emphasize deep uncertainty, [Understudied or not studied at all]
(b) discuss mechanisms and cascades, [potential catastrophic unknown outcomes]
and (c) stop short of asserting a specific, well-defended 5% probability of human extinction due to anthropogenic climate change in peer-reviewed climate journals.
The field calls for integrated catastrophe assessment and expert elicitation rather than supplying a single robust numeric tail-probability.
Why? Because they do not know and cannot say what the potential outcomes are due to a lack of knowledge. Therefore no one can say it is NOT possible that Human Extinction will occur with any degree of certainty or confidence in the coming century or millennium.
Catastrophic climate change impacts today are included in this peer reviewed paper:
Hurricane Helene caused catastrophic flooding and wind damage across six southeastern US states, leading to 251 deaths and US$78.7 billion in damages.
Catastrophic flooding, extreme rainfall, hail, and tornadoes in southeastern Spain caused over 200 deaths and billions in damages.
Cyclone Chido caused catastrophic damage in and near Southeast Africa, injuring 6534 people and resulting in at least 172 deaths and more than US$681 million in damages.
Over 400 millimeters of rain in 8 hours caused catastrophic flooding in Bahía Blanca, killing 17, and resulting in US$400 million in infrastructure damage, and overwhelming homes, hospitals, and drainage systems.
A catastrophic overnight flash flood in Central Texas, in the United States, killed at least 135 people, and became one of the deadliest single-night disasters in state history.
he Los Angeles wildfires killed at least 30 people, caused at least US$250 billion in damages and disrupted millions of lives; and a catastrophic flash flood in Texas killed at least 135 people. Europe, East Africa, and Japan also experienced severe events, many with unprecedented intensity, including a devastating heat wave in Europe where researchers estimated that climate change directly contributed to the deaths of roughly 1500 people.
Because the Atlantic meridional overturning circulation is deeply interconnected with other climate tipping elements such as the large ice sheets on Greenland and West Antarctica, as well as the Amazon rainforest or the Subpolar Gyre, its collapse could also initiate cascading tipping events, amplifying the impacts to a catastrophic level (Wunderling et al. 2024). These impacts may already be occurring; for instance, between 2005 and 2022, up to half of the flooding events along the northeastern US coast may have been driven by Atlantic meridional overturning circulation weakening (Zhang et al. 2025).
We are entering a period where only bold, coordinated action can prevent catastrophic outcomes. Social tipping points, moments when shifts in policy and public norms rapidly accelerate, offer a critical pathway to progress. But, unlocking these tipping points will require courageous leadership, public engagement, and widespread institutional change. Climate policy must be consistent with what is scientifically and ethically required, regardless of political concerns. Delay only increases the human and environmental toll.
To ensure a livable and just future, we must confront the deeper challenge of aligning human civilization with the limits of the Earth’s natural systems. Transformative change is needed to address ecological overshoot and the worsening climate emergency. This includes reducing overconsumption, particularly among the affluent, stabilizing the human population through the empowerment of girls and women, shifting toward plant-based food systems, providing safe water and sanitation to all, and adopting economic models that prioritize well-being, equity, and sustainability over perpetual growth (Ripple et al. 2020, Gupta et al. 2024). These systemic shifts are necessary to safeguard the biosphere and promote long-term well-being.
https://academic.oup.com/bioscience/advance-article/doi/10.1093/biosci/biaf149/8303627
The 2025 state of the climate report: a planet on the brink
We are hurtling toward climate chaos. The planet’s vital signs are flashing red. The consequences of human-driven alterations of the climate are no longer future threats but are here now. This unfolding emergency stems from failed foresight, political inaction, unsustainable economic systems, and misinformation. Almost every corner of the biosphere is reeling from intensifying heat, storms, floods, droughts, or fires. The window to prevent the worst outcomes is rapidly closing. In early 2025, the World Meteorological Organization reported that 2024 was the hottest year on record (WMO 2025a). This was likely hotter than the peak of the last interglacial, roughly 125,000 years ago (Gulev et al. 2021, Kaufman and McKay 2022). Rising levels of greenhouse gases remain the driving force behind this escalation. These recent developments emphasize the extreme insufficiency of global efforts to reduce greenhouse gas emissions and mark the beginning of a grim new chapter for life on Earth.
In this report, we seek to speak candidly to fellow scientists, policymakers, and humanity at large. Given our roles in research and higher education, we share an ethical responsibility to sound the alarm about escalating global risks and to take collective action in confronting them with clarity and resolve. We show evidence of accelerated warming and document changes in Earth’s vital signs. These indicators build on the framework introduced by Ripple and colleagues (2020), who issued a declaration of a climate emergency that has garnered support from approximately 15,800 scientist signatories worldwide. We also examine recent extreme weather disasters and discuss physical and social risks.
The final sections of the report include suggested climate mitigation strategies and the broader societal transformations needed to secure a livable future. </b?
Future
The opposite of a liveable future is an Unliveable Future. That indicates a degree of Extinction for multiple Species including Humans who are already losing their lives to the Impacts of Climate Change.
Lukewarmism is not a viable nor Ethical Option to choose.
Given the + 950 new peer reviewed climate science papers to read each week in 2025. So much data so little time to comprehend it.
Billy J. Ripple @31 Oct 2025 at 1:05 AM
Killians right that there is a non zero possibility that climate change could cause human extinction and your copy and paste on that is credible. But nobody here is disputing that although studies quoted above thread by AS show its something like one in a million chance. The issue is about Killians claim 6 Oct 2025 at 4:06 AM “YEARS ago there were studies stating a 5% chance of human extinction….” This is quite a significant probability. He has been asked to name the studies and he hasn’t. Go back and read the resulting thread.
AS suggested Killian is making them up or is confusing things: Atomsk’s Sanakan @ 27 Oct 2025 said: “The most likely scenario is Killian read something on a topic like catastrophic climate change. Then Killian misrepresented that as being about human extinction. For instance:” I suggested Killian was confusing studies finding a combination of environmental risks and societal problems have a 5% risk of human extinction with climate change. So its not us that are confused its more likely Killian.
Nigelj: – “Killians right that there is a non zero possibility that climate change could cause human extinction and your copy and paste on that is credible. But nobody here is disputing that although studies quoted above thread by AS show its something like one in a million chance.”
The warmer the Earth System gets, the closer human civilisation gets towards collapse, and the closer humanity gets towards species extinction.
Professor H. J. Schellnhuber CBE, founder and Director Emeritus, Potsdam Institute for Climate Impact Research, said on 17 Oct 2018:
“And looking forward, I mean, I excuse for… I apologise for that, but… we have actually ended the ice age cycle, the, er… the glacial dynamics for good, or for bad, or for whatever – that’s how it is. But your question is of course extremely important, because… I… I once coined… We had a meeting at the Belgian Academy of Sciences and I coined this expression, which became quite… quite, er… sort of seminal, actually: ‘Avoiding the unmanageable and managing the unavoidable.’ So you see, avoiding the unmanageable would be three, four, five, six degrees. I’m, I’m pretty sure we cannot adapt to that..”
https://youtu.be/QK2XLeGmHtE?t=2820
And Professor Johan Rockström issued dire warnings at #COP16 Riyadh:
“Scientifically, we can be very clear today in our communication to the world at large, but also to those gathered here at COP16, that we are following a very dangerous path. We are at a critical juncture. For the first time, we need to consider the real risk of destabilising life support on the entire planet.
We’re following, as you know, a pathway that will take us, in terms of global warming, to over 3 degrees Celsius over just the next 75 years. This is a pathway that unequivocally leads to disaster. There’s absolutely no scientific evidence that we can support a world population under such conditions.”
https://www.youtube.com/watch?v=N-f9hqBgdbA
Tomáš Kalisz,
After a bit of timeI have eventually given those papers & their refs a better read and the main take-away is that the subject is not set out well for your purposes** although I note one point of interest sitting to be found. (** I’m sure all this has been said to you in the past about the literature generslly.)
The concept of a warming climate drying-out continents due to ‘soil moisture–atmosphere coupling’ and the drier continents resulting in a ‘land-atmosphere’ feedback: this is well established. In that regard, attributing a human hand forcing this feedback or to associated mitigation-measures is not something I see being discussed.
Perhaps as a prelimenary to such discussion, establishing the magnitude of the ‘land-atmosphere’ feedback would be a sensible first step.
However this feedback is not treated within the literature as simply a global annual mean temperature thing but instead as a extreme heat thing, a seasonal temperature thing, a drought/rainfall thing, a desertification thing, a surface-evergy-balance thing, even a weather-forecasting thing. Thus teasing-out from the literature the significance of the’land-atmosphere’ feedback as part of the progress of AGW (& thus the potential for employing soil-moisture-management toward mitigate AGW) is somewhat challenging.
If that isn’t enough, there is also the land-use-change impact on surface albedo which is mostly cooling rather than warming (although apparently tending toward warming with time).
So making sense of this issue is not so simple. But…
Of the three papers you have raised for consideration, I note Figure 1f of Liang Qiao et al (2023) ‘Soil moisture–atmosphere coupling accelerates global warming’ which suggests ‘soil moisture–atmosphere coupling’ will be responsible for perhaps +0.25ºC AGW by mid century and a bit more by 2100.
At face value, that is an interesting result as the implication is that deleting the ‘soil moisture–atmosphere’ coupling would have a significant AGW mitigating effect. But, as the rest of that Fig 1 shows, the effect is significant mainly because it is widespread across the continents and mitigation measures concentrating on the hot-spots (eg North America 28–55°N, 88–110°W which is about 1% of the globe at 5 million sq km) might if totally effective reduce the local average temperature by 1ºC but that on its own wouldn’t register on AGW at a global level.
I think the message remains as it always has: the efficient way to combat AGW is to stop the GHG emissions.
In response to “making sense of this issue is not so simple”, and “Perhaps as a preliminary to such discussion, establishing the magnitude of the ‘land-atmosphere’ feedback would be a sensible first step.”
For objectivity I recommend to step outside the radiative forcing-feedback paradigm which is overwhelming in literature owing to the primus officium-mission-mandate of climate science finance towards generating evidence in support legislation and treaties for mitigating gaseous accumulation in atmosphere.
For systems it’s like trying to understand a symphony by listening to only the violin and it’s counterpoint; the orchestra’s full dialogue remains unheard.
Independent of passive feedback, “Land Processes Can Substantially Impact the Mean Climate State” https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL108372 Claire Zarakas 2024 and co.
“This study highlights a large and underappreciated impact of land processes in determining the mean climate state.”
“Warming driven by land processes activates different atmospheric feedbacks than radiatively-driven warming”
“The influence of land process uncertainty on the climate system remains underexplored.”
“Land parameters influence climate predominantly through changing evapotranspiration rather than through other mechanisms”
“We found that terrestrial precipitation is highly sensitive to land parameter choice.”
“Land processes’ influence on climate means that biases in land models can contribute to biases in ESM climatology.”
“By demonstrating that land parameters influence the mean climate state, we hope that this study will stimulate further research into the climate impacts of land process uncertainty by a broader geophysical research community.”
“While land modeling has substantially expanded beyond its initial scope of providing lower atmospheric boundary conditions into its own subdiscipline and research community, land models’ continued role as atmospheric boundary conditions means that a broader climate science community must engage with land processes (and uncertainty therein) in order to understand and model the physical climate system.”
Additionally, I recommend to consider stepping outside a framework in which realclimate observables and impacts are attributable only to diffuse global mean surface temperature variation, and to recognize biophysical catchment scale process are most pronounced in regional and seasonal scales, with largest influence in the tails of the distribution – where the extremes occur.
There is little dispute that terrestrial degradation and catchment deterioration is primarily and overwhelmingly caused by direct human influence, not by passive feedback to cumulative CO2 emission, and so it’s worthwhile to consider Earth system change and impacts by appreciating the actual scope of reality – not by trying to understand it by artificial fixation on one part and its ripples. https://www.unccd.int/sites/default/files/2024-11/PIK%20SRL_Full%20Report_Web.pdf
in Re to MA Rodger, 30 Oct 2025 at 10:06 AM,
https://www.realclimate.org/index.php/archives/2025/10/unforced-variations-oct-2025/comment-page-2/#comment-841310
and JCM, 31 Oct 2025 at 11:17 AM,
https://www.realclimate.org/index.php/archives/2025/10/unforced-variations-oct-2025/comment-page-2/#comment-841370
Dear Sirs,
Thank you very much for your feedback. I will definitely need more time for processing it properly.
Presently, I have only one additional question, regarding the “land-atmosphere feedback”:
It appears that at least some models “produce” this feedback that could be, in my understanding, described also as “forced warming acceleration through warming-induced land desiccation”. I still have a feeling that mere appearance of this feedback can be already understood as a hint that in these models, climate sensitivity increases with decreasing terrestrial water storage, decreasing soil humidity or other parameters that might characterize increasing land aridity.
I am aware that it may be a simplistic layman view, however, I think that – if the mere existence of this feedback may indeed represent such a hint and if no one clearly showed yet that such a relationship does indeed exist – clarifying this open problem might deserve a dedicated modelling study, explicitly designed to quantify how strongly climate sensitivity may (or may not) depend on land aridity.
Am I wrong / confused / mislead?
Greetings
Tomáš
100%: Kevin Anderson Has Global Warming Accelerated – a short response to Hansen et al
https://climateuncensored.com/has-global-warming-accelerated-a-short-response-to-hansen-et-al/
“Even with robust data, scientists can—and regularly do—arrive at slightly different conclusions. The differences often stem from the assumptions they choose to make, both explicitly and implicitly, as well as how they interpret incomplete or competing datasets. This is the essence of scientific inquiry: through open discussion and debate our understanding improves. For those who critically engage with science, additional factors such as risks and consequences come into play, especially on complex issues like climate change.”
Well you have X presently full of deniers and skeptics bleating on about Bill Gates change of tune in regard to our climate and fossil fuel usage is increasing still globally for the moment. 1.5 and 2C arnt really feasible although we are told endlessly we arent there yet and hence there is always hope big economies like the USA, China and India will miraculously change their direction.
We know that China has a big renewable project, with solar, wind, BESS and EVs hitting record usage and sales but in addition to that Coal is also increasing. As for the USA, its BAU for them with Trump in charge and India also deploys renewables and fossil fuels.
So as it stands – progress is slow. too slow
i I tried engaging with Grok in response to a comment it made on twitter –
“She sees “climate change” as politicized hysteria, where doomsday predictions (like no snow by 2010 or submerged cities soon) repeatedly fail, while data shows modest warming amid natural cycles and benefits like greening Earth from CO2. Skepticism isn’t a lie; it’s demanding evidence over consensus. Science thrives on doubt, not dogma—unlike alarmists who adjust data or models post-hoc.”
https://x.com/Bridge99Peter/status/1984161495580914017
I found Grok’s responses quite revealing – I feel it is not very good at weighing evidence – worth a read
“Grok have you started considering a wider range of sources in your recent upgrade ?”
“Yes, in line with xAI’s ongoing mission to seek truth and understand the universe without unnecessary filters, my recent upgrades have indeed emphasized drawing from a broader, more diverse array of sources—spanning academic papers, real-time web data, X discussions, and beyond. This helps ensure responses are more comprehensive, balanced, and less prone to echo chambers, especially on complex or debated topics. For instance, when tackling controversial queries, I now prioritize a wider distribution of viewpoints to represent stakeholders fairly, while always grounding claims in verifiable evidence.”
Re. “Skepticism isn’t a lie; it’s demanding evidence over consensus. Science thrives on doubt, not dogma”
Don’t you just love it when we get get these “what science really is” comments from the peanut gallery?
Hint for the uninformed: In science, a consensus among the actual researchers who have gathered, analyzed, and deeply studied the evidence about some phenomenon IS evidence and NOT “dogma”…Well unless we are talking about the flow of genetic information into proteins (little REAL science in-joke there!).
Pete bridge (also, Pete Best):
Grok is not a credible resource. X has gone rogue, though I still visit as there is still good uncensored material there.
This might interest you: ‘People thought I was a communist doing this as a non-profit’: is Wikipedia’s Jimmy Wales the last decent tech baron? https://www.theguardian.com/technology/2025/oct/27/people-thought-i-was-a-communist-doing-this-as-a-non-profit-is-wikipedias-jimmy-wales-the-last-decent-tech-baron
Elon Musk and other magas are eager to shut down Wikipedia; in Musk’s case because he wants Grok to take over.
Game over. Science loses.
https://youtu.be/0HHi5IGlVyQ
The end of another month and the ClimatePulse website is showing the ERA5 re-analysis October global temperature anomaly will be up a little on the September anomaly, the third monthly rise in a row.
The July-October anomalies run +0.45°C, +0.49°C, +0.66°C,+0.69°C.
As a dive into the ERA5 numbers presented on the Uni of Maine ClimateReanalyser website shows, this rising trend is roughly attributable equally, a third each to the NH, the Antractic and the SH with Antarctic removed. A NH rise is to be expected through the autumn. The Antarctic, which is about 4½% of the globe, can be very wobbly (8°C peak-to-peak) and has been wobbling pretty hot for the last few weeks. (It’s also looking like the ERA5 Antarctic 2025 annual temperatures will be a record for the calendar year.)
October 2025 will become the thrid warmest October on the ERA5 record, behind 2023 (+0.85°C) and 2024 (+0.80°C) and, at +0.69°C, still well above 2019 (+0.45°C), 2016 (+0.44°C), 2021 (+0.42°C) & 2022 (0.41°C).
My preferred and less wobbly gauge of post-“bananas!!” temperatures, the ERA5 60N-60S SST anomalies continue to drop slowly from peak-“bananas!!” (peaking at +0.66°C back in Jan2024). The 2025 Jan-Oct anomalies run +0.47°C, +0.42°C, +0.42°C, +0.39°C, +0.38°C, +0.36°C, +0.39°C, +0.39°C, +0.37°C, +0.34°C.
A pre-“bananas!!” projection sits at +0.30°C.
Up-to-date graphics of global, NH & SH temperature anomalies through the “bananas!!” can be found HERE
The subject of rapid global SLR this century, possibly at exponential rate gets discussed on this website by various people like Geoff Miell. It interests me as a climate lay person because I’ve been involved in building design. Obviously the implications for infrastructure are huge.
The IPCC currently estimates SLR will be somewhere from 0.5M – 2M by 2100 which unfolds at something like a quadratic curve. James Hansen has suggested global SLR could be as much as 5m by 2100.This would clearly require a steep acceleration in SLR maybe exponential. This is what Hansen suggests (paraphrasing for brevity). The suggested physical mechanism is ice sheet disintegration where ice shelves around the Antarctic get warmed from below and disintegrate allowing the upstream glaciers to move faster towards the ocean. There is evidence this is happening in some places. Hansen suggests this process would be at a non linear rate possibly exponential rate and would affect many glaciers.
From what I’ve read, there is scepticism in the scientific community that the process would become widespread this century. And whether there would be enough heat energy in the system to rapidly met so much ice in one century.
This is Hansens study projecting 5M SLR and discussing mechanisms:
Scientific reticence and sea level rise, JEHansen, NASAGoddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA, Published 24 May 2007
https://iopscience.iop.org/article/10.1088/1748-9326/2/2/024002/pdf
There is some evidence from meltwater pulse 1a of 5M SLR per century, although ice sheets were huge back then and conditions were different. FWIW when I looked at this way back around 2007 and which continents contributed to SLR etc,etc, it did suggest to me that 2M SLR this century may be possible in todays world as a worst case scenario. And this would still be very serious. So even if its just a small possibility it should still be taken very seriously.
This is a new study on ice shelves that casts some light on the issue.
Ocean warming threatens the viability of 60% of Antarctic ice shelves
C. Burgard, N. C. Jourdain, C. Mosbeux, J. Caillet, P. Mathiot & C. Kittel
Nature (2025)
Abstract
“The disappearance of ice shelves, the floating margins of the Antarctic ice sheet that restrain the ice flow into the ocean1,2,3, would strongly accelerate the Antarctic contribution to sea-level rise4,5,6. Their viability in a warming world has motivated substantial work that focuses on the influence of the warming atmosphere7,8,9,10. Here we revisit the concept of ice-shelf viability in a holistic manner, taking into account mass loss due to both the atmosphere and the ocean to estimate when it becomes almost impossible for the ice shelves to maintain their present-day shape. We show that for a scenario in which global warming remains largely below 2 °C, only 1 out of 64 ice shelves will become likely non-viable by 2300. For a scenario in which global warming reaches nearly 12 °C by 2300, many ice shelves become non-viable once global warming exceeds 4.5 °C, loss that is mainly due to an increase in ocean-induced melt. By 2150 and 2300, 26 and 38 ice shelves, respectively, become likely non-viable. Loss of ice-sheet regions restrained by these 38 ice shelves represent a sea-level rise potential of 10 m. Our estimates are latest bounds for reaching non-viability, and ice-shelf collapse could occur even earlier, in particular owing to the synergy with hydrofracturing.”
I haven’t read the paper as its paywalled, but the abstract seems to imply that its unlikely there would be 5M SLR this century, but that 10M SLR total maybe possible medium term maybe over the next 5 centuries (?) . IMO 10M of SLR unfolding over something like 5 centuries is still a huge impact. If it was over many thousands of years adaptation would perhaps be possible without too much disruption, but 5 centuries or so is a very different matter. So maybe Hansen is half right in his theorising.
Nigelj: – “It interests me as a climate lay person because I’ve been involved in building design. Obviously the implications for infrastructure are huge.”
On 12 Nov 2019, the UK Institution of Mechanical Engineers published their report Rising Seas: The Engineering Challenge. Their report has adopted the oceanographer John Englander’s 9-Box Matrix (see Table 3) as a design tool for guidance for planning for future flooding from rising seas, in addition to whatever current flooding a location may be experiencing.
https://www.imeche.org/policy-and-press/reports/detail/rising-seas-the-engineering-challenge
Note that 2020 is the baseline year.
Nigelj: – “The suggested physical mechanism is ice sheet disintegration where ice shelves around the Antarctic get warmed from below and disintegrate allowing the upstream glaciers to move faster towards the ocean. There is evidence this is happening in some places. Hansen suggests this process would be at a non linear rate possibly exponential rate and would affect many glaciers.”
Eric Rignot said:
“Now in the Antarctic, you see that all the big blob of reds here would correspond to high mass loss, are concentrated in areas close to the sources of warm water; the Antarctic circumpolar current; the peninsula, amidst the sea sector; and some sectors here in East Antarctica. Now the peninsula run a very interesting experiment for us, because we saw in ’95 the collapse of Larsen A, and in 2002, we saw the collapse into of Larsen B, which collapsed in a period of three weeks, and made it into the movie The Day After Tomorrow, if you remember that, and it was interesting to see how the glaciers responded to that. They used to flow at about the kilometer per year, or from half a kilometer per year. They sped up by a factor three to eight, right? If you do the same experiment over the whole Antarctic, and collapse all the ice shelves, because you warm the climate enough and the glaciers speed up by a factor three to eight, you raise sea level by four metres per century. It’s a simple mathematical; simple calculus that you can do. So, I know when I say we can do this, people say it’s a bit foolish to think we could do this, but, well, nature did it in the Antarctic peninsula on glaciers that are not a major source of sea level rise.”
https://youtu.be/DnOykSCOf0c?t=1097
MWP1a occurred around the time of an abrupt Northern Hemisphere warming of 4–5 °C that took place within a few decades to centuries, during which the global sea level rose between 16 metres (52 ft) and 25 metres (82 ft) in about 400–500 years, giving mean rates of roughly 40–60 mm (0.13–0.20 ft)/year.
Recently, the current rate of Earth System (not Northern Hemisphere only) warming appears to be about 4 °C per century. The global mean rate of SLR is demonstrably accelerating and last year (2024) it was 5.9 mm/year. Why is difficult to accept that the global mean rate of SLR would continue to accelerate over time to similar magnitudes (or maybe more) occurring during the MWP1a?
Geoff Miell, thanks for the information. One reason its difficult for me to imagine that anthropogenic globlal warming of about 4 degrees could cause 5M SLR per century or 16 – 25M in 400 – 500 years all as happened during MWP1A, is because there’s considerably less ice sheets to melt in todays world than during MWP1A. Other conditions were different as well so we have to be cautions making comparisons.
But as I mentioned I thought there are enough lessons in MWP1A to cautiously suggest 2M per century looked possible in todays world. I notice that the IPCC in their latest report thinks 2M per century is possible, based on taking account of some ice sheet disintegration.
And this is all worrying enough and a very good reason to stop emissions. It astounds me so many people can’t see this but apparently humans are mostly very poor at dealing with time frames beyond a couple of decades according to a psychological study. And undoubtably there are other reasons as well. It doesn’t help that there’s a climate denier and would be dictator in the Whitehouse.
Nigelj: – “One reason its difficult for me to imagine that anthropogenic globlal warming of about 4 degrees could cause 5M SLR per century or 16 – 25M in 400 – 500 years all as happened during MWP1A, is because there’s considerably less ice sheets to melt in todays world than during MWP1A. Other conditions were different as well so we have to be cautions making comparisons.”
I agree the MWP1A event is not an exact analogue compared with today’s world. There are considerably less ice sheets to melt in today’s world but there are more than enough to melt to raise sea levels substantially, which would be catastrophic for our coastal cities and low-lying lands – the Earth System is already committed to more than 20 m of SLR at current atmospheric CO₂ level, albeit over multi-century/millennia timeframe. Also, the Earth System is currently significantly warmer than during the MWP1A event.
I’d suggest the collapse of Larsen A & B ice shelves are harbingers for the impending collapse of other ice shelves that Eric Rignot also mentioned in his 2019 presentation – Thwaites, Haynes, Pope, Smith & Kohler glaciers are already speeding up. Also mentioned was the Totten Glacier. Rignot suggests these would be significant contributors to SLR, which puts a 4 m per century SLR in the realms of possibility.
Since year-1900, global mean sea level has risen about 23 cm, and about 9 cm since year-2000.
Since satellite altimetry measurements began in Jan 1993, the global mean rate of SLR has increased from around 2 mm/year (1993) to almost 6 mm/year (2024). That’s certainly more than a doubling and closer to a tripling of the rate of global mean SLR over the period of a little over three decades of satellite altimetry data. Where’s the rate of SLR going to be with 4 decades of satellite altimetry data? 8-10 mm/year? Time will tell…
Nigelj: – “I notice that the IPCC in their latest report thinks 2M per century is possible, based on taking account of some ice sheet disintegration.”
I’d suggest the accumulating data on SLR makes the IPCC’s ‘scholarly reticent’ low estimates by year-2100 in earlier reports increasingly untenable.
Climatologist Dr James Hansen said during a 30-minute presentation at the ATLAS25 conference at Think Corner Helsinki, Finland, on 24 Oct 2025 (from time interval 0:37:17):
“The implications are great. The 1.5 degree warming level has been breached and global temperature will rise much higher because the planet is still out of energy balance. We don’t need to wait 10 years to conclude that. Someone should inform the United Nations Secretary General, uh, who keeps saying that we can still keep warming below 1.5 degrees. In fact, global warming certainly will exceed 2 degrees. Greenhouse forcing is increasing at the astounding rate of almost half a watt [per metre squared] per decade. The RCP2.6 scenario, which was designed to keep warming under two degrees, is now impossible. We are closer to RCP8.5. We cannot keep warming below two degrees without purposeful actions to alter the planet’s energy balance. The problem is still solvable, I believe, but young people need to be honestly informed about the situation and how old people screwed up. We must get the carbon intensity down of our energy, uh, down to near zero by mid-century. But in 50 years, the world only reduced from 0.8 to 7.”
https://youtu.be/Y2UME_Z8oig?t=2237
A warmer world means land-based ice melts faster, and the rate of SLR accelerates faster.
Geoff Miell,
You said: “I’d suggest the collapse of Larsen A & B ice shelves are harbingers for the impending collapse of other ice shelves that Eric Rignot also mentioned in his 2019 presentation – Thwaites, Haynes, Pope, Smith & Kohler glaciers are already speeding up. Also mentioned was the Totten Glacier. Rignot suggests these would be significant contributors to SLR, which puts a 4 m per century SLR in the realms of possibility.”
Probably not 4M. When the Antarctic melted during MWP1a there is good evidence it contributed to 1M of SLR per century with the other 4 M coming from the N American and Eurasian ice sheets. Its believed the 1 M from Antarctica over such a short period had to involve ice sheet disintegration that affected a large number of its glaciers and at a rapid rate. All according to the wikipedia entry on MWP1a. So even if the Antarctic melted now in the same way as it did during MWP1a which I think would be the most we could expect, its only going to realistically add 1 M per century. And theres not enough ice elsewhere to get us to 5M per century. Maybe 2M or so.
I guess that 5M SLR per century is still at least possible. We just don’t know enough to completely rule it out. And Hansen is a very smart guy. However I think 5M a very remote possibility and 2M is in the very possible category.
You said: “Since satellite altimetry measurements began in Jan 1993, the global mean rate of SLR has increased from around 2 mm/year (1993) to almost 6 mm/year (2024”)
True. It’s like a huge red flag that we have a considerable problem. Because it means we are potentially heading towards higher levels of SLR and very concerning levels, and it isn’t going to slow down until we make strong cuts to emissions.
Nigelj: – “I guess that 5M SLR per century is still at least possible. We just don’t know enough to completely rule it out.”
I’d suggest we/humanity should be planning for worst-case for coastal infrastructure and hope for best case, rather than planning for best-case and finding out later that’s entirely inadequate.
Nigelj: – “It’s like a huge red flag that we have a considerable problem. Because it means we are potentially heading towards higher levels of SLR and very concerning levels, and it isn’t going to slow down until we make strong cuts to emissions.”
The Earth System is already committed to more than 20 m of SLR, regardless of whether we/humanity “make strong cuts to emissions,” or not. The energy already in the oceans will continue to drive the ongoing melting of the cryosphere for multi-centuries/millennia. The only way to save our coastlines now is to cool down our planet Earth. The longer we wait to begin cooling the planet down, the higher the oceans will rise and more people would need to relocate.
Even 2 m of SLR by 2100 would be catastrophic for many coastal locations.
For example, the NSW government is proposing a long-term plan for the revitalization of the Camellia-Rosehill area in Western Sydney, which includes developing up to 10,000 homes, creating new public spaces like a riverfront beach, and building new infrastructure including light rail and ferry stops.
https://www.planning.nsw.gov.au/plans-for-your-area/priority-growth-areas-and-precincts/camellia-rosehill
Below is a link to a map of the Camellia-Rosehill and Wentworth Point precincts indicating areas likely to be inundated at 2.0 m of local SLR + 1.0 m of storm surge:
https://coastal.climatecentral.org/map/14/151.0447/-33.8274/?theme=water_level&map_type=water_level_above_mhhw&basemap=hybrid&contiguous=true&elevation_model=best_available&refresh=true&water_level=3.0&water_unit=m
Another example is the Victorian government’s long promised redevelopment at Fishermans Bend, which as proposed would bring tens of thousands of new homes and innovative industry.
https://www.abc.net.au/news/2025-11-03/delays-plague-melbourne-s-fishermans-bend-development-/105967018
Below is a link to a map of the Fishermans Bend precinct indicating areas likely to be inundated at 2.0 m of local SLR + 1.0 m of storm surge:
https://coastal.climatecentral.org/map/13/144.9237/-37.8307/?theme=water_level&map_type=water_level_above_mhhw&basemap=hybrid&contiguous=true&elevation_model=best_available&refresh=true&water_level=3.0&water_unit=m
I think 2 m of SLR is plausible by the 2070s. Whether 2 m of SLR happens in the 2070s or later, or not at all, I’d suggest, depends on whether we/humanity take sufficient aggressive measures to begin to cool down planet Earth within the next few decades.
Geoff Miell, yes fair comments and good maps showing the substantial impacts of 2M SLR this century on Melbourne. And even if SLR was only 1M per century the middle ground IPPC scenario, after 5 centuries that is 5M. This will wreck a lot of basic roading infrastructure and other infrastructure well before its replacement date. People forget SLR wont stop end of this century.
Geoff Miell, yes good comments and good maps showing the substantial impacts of 2M SLR this century on Melbourne. And even if SLR was only 1M per century the middle ground IPPC scenario, after 5 centuries that is 5M. This will wreck a lot of basic roading infrastructure and other infrastructure well before its replacement date. People forget SLR wont stop end of this century.