There has been a sudden increase in the rate of sea level rise

[John Nissen]

Hello everyone,

This is extremely bad news; much worse than I feared. The rapid rise cannot be due to global temperature rise which gives rise to ocean expansion and steric SLR, though that is serious enough to give us at least a metre by 2100 when global temperature will pass 4C at the current warming rate. SLR through ice melt is even more serious.

The planet has lost albedo at an alarming rate, some due to reduced cloud cover and some due to snow and ice retreat. The retreat on land has positive feedback and means accelerated meltwater discharge. This is what we are seeing in their figures and its worse than I had assumed. This is a crisis of the highest order. Rapid SAI deployment is now are best chance of saving the future for our younger people. 

Love should be driving motive: it is for me, especially having 2 grandchildren late in the day. I see SAI as a godsend.

Cheers John 

There has been a sudden increase in the rate of sea level rise | New Scientist https://share.google/MhJI1kGF1mpGuqDKn 

[rob...@rtulip.net]

Thanks John. 

 

The New Scientist article reports on an open source Nature article at https://www.nature.com/articles/s43247-025-03149-5

 

The Nature article reports measurement of sea level rise increasing from 2.9 mm/y over 1993–2011 to 4.1 mm/y over 2012–2024.  It is good to have such precise data. 

 

4.1/2.9 = 41% increase over about  20 years. That is a rate of increase of about 2% per year.  Continued at either linear or exponential rates of increase, that would lead to just over one metre SLR per century, within IPCC scenarios. 

 

That is less than one tenth of the fastest historic rate of about 50mm/ year in Meltwater Pulse 1A, when sea level rose 30 metres in about six centuries to 13800 years before present.

 

One metre SLR per century is less than some experts predict.  We should worry the fat tail risk that the unprecedented rate of increase in GHGs could cause much faster collapse of ice sheets as part of combined planetary tipping processes.

 

I have been exploring Pleistocene sea level rise in my series of weekly articles at Drowned Worlds, as a way to study our amnesia about the past and the implications of rapid sea level rise. My next chapter will jump to a 3 metre SLR in 2150 scenario.

 

Regards

 

Robert Tulip

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[Tom Goreau]

Hardly sudden, this has been a smooth gradually increasing exponential, at least so far!

 

It won’t stay that way, expect sudden jumps when entire ice sheets slip and slide into the sea, as happened in the past.

 

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[John Nissen]

Precisely, Tom.

The Climate Central map for 2050 is bad enough [1].  And that is on continued smooth progression.  I've looked at London, and the authorities need to start preparations now for building a barrage down-stream from the existing barrier or across the Thames Estuary, if London is to be protected from flooding.  For some areas, like the whole of the east coast of the North Sea, protection looks impossible.  And that is without sudden jumps in sea level.

Prevention of ice sheet collapse, coupled with global cooling, has to be attempted.  SAI is essential and relatively cheap compared with avoided damage: in the ratio of 1 to100 or more.  But also some barriers need to be built as a precautionary measure, especially if SAI deployment is delayed or found wanting.

Cheers, John

[1] Climate Central map

https://coastal.climatecentral.org/map/6/2.8674/52.5234/?theme=sea_level_rise&map_type=coastal_dem_comparison&basemap=roadmap&contiguous=true&elevation_model=best_available&forecast_year=2050&pathway=ssp3rcp70&percentile=p50&refresh=true&return_level=return_level_1&rl_model=coast_rp&slr_model=ipcc_2021_med 

[chris....@btinternet.com]

John,

 

The Environment Agency has a  Thames Estuary 2100 (TE2100) Plan (https://www.gov.uk/government/collections/thames-estuary-2100-te2100) that includes a new larger barrier further downstream in the final phase of the project (2050-2100).

 

Chris.

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Virus-free.www.avast.com

[Tom Goreau]

• Article

• Published: 11 May 2026

Stratospheric cooling and amplification of radiative forcing with rising carbon dioxide

• Sean Cohen, 
• Robert Pincus & 
• Lorenzo M. Polvani 

Nature Geoscience volume 19, pages507–512 (2026) 

Abstract

The cooling of the stratosphere in response to increasing carbon dioxide concentration is a fingerprint of human effects on climate. However, the mechanisms that control the magnitude and vertical structure of this cooling have not been clear. Here we use idealized models of spectroscopy and radiative transfer to explain the sensitivity of stratospheric temperature to carbon dioxide concentration. We find that stratospheric cooling is mainly driven by the distribution of mass absorption coefficients in the primary carbon dioxide band and modulated by the longwave cooling of water vapour and ozone in other parts of the spectrum. These spectral mechanisms explain why the stratosphere cools more aloft than it does below, why each doubling of carbon dioxide yields roughly 0 to 8 degrees Kelvin of cooling across the depth of the stratosphere and why stratospheric cooling increases the top of atmosphere radiative forcing of carbon dioxide by about 50%. This theory implies that stratospheric cooling is not a fundamental consequence of increasing the optical thickness of a greenhouse gas but rather the unique result of the spectroscopy of that gas.

 

 

From: John Nissen <johnnis...@gmail.com>

Date: Wednesday, May 13, 2026 at 14:55
To: Tom Goreau <gor...@globalcoral.org>

[Veli Albert Kallio]

"The average global sea level has already risen by more than 0.2 metres over the past 15 years as a result of global warming."

The sunken cities of the Arabian Sea site saw similar 0.2 metre rise on sea level with houses floors raised accordingly, then the next pulse was 2 metre rise when the houses were rebuilt on stilts, this was followed by the third pulse when the structures were immersed into deep water. This region is the triangle with Oman - Pakistan - India with the Harappan style sites seen on the Bay of Cambay area. Strong sea currents have hindered more detailed studies in the area. At the third water pulse the site was beneath the level of wave action and not pulverised as would have happened if the site remained long on the margin of the sea shore (as storms pulverise and scatter clay brick made soft structures).

---

From: healthy-planet-...@googlegroups.com <healthy-planet-...@googlegroups.com> on behalf of John Nissen <johnnis...@gmail.com>
Sent: 13 May 2026 11:46

To: Peter Wadhams <peter....@gmail.com>; Metta W Spencer <mspe...@web.net>; Planetary Restoration <planetary-...@googlegroups.com>
Cc: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>; JOHN ENGLANDER <johneng...@gmail.com>

Subject: [HPAC] There has been a sudden increase in the rate of sea level rise

 

--

[John Nissen]

Thanks, Chris and Albert,

Chris, the map of the London area produced by the UK environment agency for 2100 (75 year forecast) [1] is remarkably similar to the Climate Central map of the same area for 2050 (25 year forecast) [2].  The latter suggests that a mighty dyke (not a barrage, my mistake) costing many $billions needs to be built across the Thames Estuary before 2050 if London is to be saved.  Preparations would need to start ASAP.

But neither forecast can take account of the sudden sea level rise from ice sheet collapse, which Albert points out has happened in the past.  There is a high risk of a large collapse of ice from the Greenland Ice Sheet triggering further collapses, possibly with some in Antarctica.  This domino effect could produce a sudden two metre rise before 2050.  The dyke would have to allow for a sudden two metre rise in sea level.  (Albert, how high was the third pulse and how much later?)

If the UK were to collaborate with other West European countries, dykes could enclose the whole North Sea [3].  This is not as mad an idea as it sounds: $500 billion or so as a precautionary measure.  But it would leave Ireland, many smaller islands, and the west half of the UK coastline unprotected.

And the dyke could only be a temporary measure. There's enough GHG in the atmosphere to ensure the melting of all polar ice, eventually raising the sea level by 60m or more.  We can only prevent such meltdown in the future if we start applying cooling intervention now, or within a few years.

If governments want to avoid catastrophic sea level rise for the peoples they govern, they need to collaborate to apply the dreaded SAI: the much-needed band-aid to lower the Arctic temperature and start to refreeze it.  If SAI deployment were started within a year or two, and quickly ramped up to full strength, the need for trillions of dollars to be spent on flood defences might be avoided.  

Look at it this way: Prompt SAI can stop the accelerating slide towards catastrophic sea level rise - a slide which could become unstoppable within a few years.

Cheers, John

[1] Thames Estuary 2100: Why we need it

https://www.gov.uk/guidance/thames-estuary-2100-why-we-need-it 

[2] Climate Central map of flood risk for 2050

Land projected to be below flood level

https://coastal.climatecentral.org/map/6/2.8674/52.5234/?theme=sea_level_rise&map_type=coastal_dem_comparison&basemap=roadmap&contiguous=true&elevation_model=best_available&forecast_year=2050&pathway=ssp3rcp70&percentile=p50&refresh=true&return_level=return_level_1&rl_model=coast_rp&slr_model=ipcc_2021_med

[3] Jon Henley and Alan Evans (Guardian, 12th Feb 2020)

Giant dams enclosing North Sea could protect millions from rising waters

https://www.theguardian.com/environment/2020/feb/12/giant-dams-could-protect-millions-from-rising-north-sea

[John Nissen]

Hi Alan,

Sudden sea level rise would come from a partial collapse of the Greenland Ice Sheet (GIS).  I believe that the most likely reason for an AMOC collapse would be such a collapse, injecting quantities of meltwater from either the west or the east side of Greenland onto the surface of the AMOC in the North Atlantic.  This meltwater would freshen the surface, and make it less liable to sink through an increase in salinity when ice meets the Arctic sea ice.  It is this sinking which is the main driver of AMOC.

The quantity of freshwater injection to trigger a change of AMOC state used to be estimated at around 0.25 Sverdrup; I haven't seen an update.  Rahmstorf is an acknowledged expert, see quote in [1].  He has written an exposition of the position, see [2].  The fear seemed to be that we are approaching a point of no return, even though the actual collapse may be much later.  But now we hear talk of the collapse being the point of no return, particularly scaring Iceland, see [3].  But there's little mention of the influence of Greenland meltwater.

However one can also compare the current situation with the Heinrich Event at the beginning of the Younger Dryas.  The Greenland Ice Sheet is clearly implicated in a partial collapse of AMOC [4].  Yet, Rahmstorf dismisses the IPCC models which make the connection, see [5] quote from [2].  Thus the field is full of controversy.  Years ago I would have trusted Rahmstorf, but now I have my doubts because of the likeness of the present situation to a past Heinrich Event. 

What I do firmly believe is that the only way to stop the slide towards collapse of both GIS and AMOC is by refreezing the Arctic.

Cheers, John

[1] Bob Henson (Yale Climate Connections, 2024)

How much should you worry about a collapse of the Atlantic conveyor belt?

https://yaleclimateconnections.org/2024/12/how-much-should-you-worry-about-a-collapse-of-the-atlantic-conveyor-belt/ 

Stefan Rahmstorf at the Potsdam Institute for Climate Impact Research is an eminent researcher who’s studied AMOC and its various modes for more than 30 years. In October 2024, discussing the specter of AMOC collapse, Rahmstorf warned: "Even with a medium likelihood of occurrence, given that the outcome would be catastrophic and impact the entire world for centuries to come, we believe more needs to be done to minimize this risk."

[2] Stefan Rahstorf (Oceanography, ~2024)

Is the Atlantic Meridional Overturning Circulation approaching a tipping point?

https://tos.org/oceanography/assets/docs/37-rahmstorf.pdf

[3] Nicola Jones (Yale Environment 360, 7th May 2026)

Why Fears Are Growing Over the Fatte of a Key Atlantic Current

https://e360.yale.edu/features/amoc-climate-change

"In November, Iceland made the unusual move of designating the risk of an AMOC shutdown a national security threat"

[4] Zhou and McManus (Science, 2024)

Heinrich event ice discharge and the fate of the AMOC

https://www.science.org/doi/10.1126/science.adh8369

[5] Rahmstorf quote from [2]

CAN CLIMATE MODELS BE TRUSTED?
Climate models have long predicted a significant AMOC slowdown in response to global warming, including a corresponding cold blob (see Figure 12 for a recent version). In fact, I wrote two commentary pieces for Nature on that topic in the 1990s (Rahmstorf, 1997, 1999), and then as now, the amount of predicted weakening differed greatly among different models. The latest, sixth IPCC report found that, even for a low emissions scenario, the AMOC will weaken between 4% and 46% by the year 2100, depending on the model. In the high emissions scenario, the reduction ranges between 17% and 55% (IPCC, 2021). The IPCC report also concluded: “While there is medium confidence that the projected decline in the AMOC will not involve an abrupt collapse before 2100, such a collapse might be triggered by an unexpected meltwater influx from the Greenland Ice Sheet.”

On Fri, May 15, 2026 at 3:24 AM Alan Kerstein <alan.k...@gmail.com> wrote:

John,

Suppose AMOC collapse is the first major tipping event. Beyond the fact that this could overshadow sea-level rise, might it cool the Arctic and warm the Antarctic to the point where Antarctic SAI becomes the priority? More broadly, with various contingencies looming, can we plan ahead confidently by extrapolating based on what seems most urgent presently?

Alan

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[Michael MacCracken]

Dear Tom et al.--Lets hope rapid sea level rise occurs at the same time that we start SRM as surely SRM will be blamed--that is the way things seem to work (or not) these days.

Mike

On 5/15/26 4:51 PM, Tom Goreau wrote:

We have YET to see sudden increase in sea level rise, but there is clear evidence of it in the past, when many inhabited coastal areas were flooded in the early Holocene.

 

The submerged Indus Valley civilization ruins off the coast of Gujarat might have been submerged by a later earthquake rather than ice cap melt. They are so buried in mud that real excavation is impossible.

 

When sudden sea level rise REALLY begins, it will be undeniable except to fools.

 

We may get a first little taste of it this year, when the El Niño just starting raises Pacific sea levels, causing more more islands to flood.

 

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[Ron Baiman]

Lol Mike! I assume you mean *does not start* as probably everyone understood, but just to make your (imho very valid concern) clear!

Best,

Ron 

Sent from my iPhone

On May 15, 2026, at 4:32 PM, 'Michael MacCracken' via Planetary Restoration <planetary-...@googlegroups.com> wrote:



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[bruceh...@yahoo.com]

How can we come to an agreement on the best value to use for the recent SLR?

 

(from a Google search)

Bruce Parker

 

 

-resto...@googlegroups.com <planetary-...@googlegroups.com> On Behalf Of Veli Albert Kallio
Sent: Thursday, May 14, 2026 10:08 AM
To: John Nissen <johnnis...@gmail.com>; Peter Wadhams <peter....@gmail.com>; Metta W Spencer <mspe...@web.net>; Planetary Restoration <planetary-...@googlegroups.com>

Cc: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>; JOHN ENGLANDER <johneng...@gmail.com>

Subject: [prag] Re: [HPAC] There has been a sudden increase in the rate of sea level rise

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[Alan Kerstein]

John,

Suppose AMOC collapse is the first major tipping event. Beyond the fact that this could overshadow sea-level rise, might it cool the Arctic and warm the Antarctic to the point where Antarctic SAI becomes the priority? More broadly, with various contingencies looming, can we plan ahead confidently by extrapolating based on what seems most urgent presently?

Alan

On Thu, May 14, 2026 at 2:16 PM John Nissen <johnnis...@gmail.com> wrote:

To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/CACS_Fxq0_CxfuTgg5oV1EKCLc4iBsfLmjciGBqk%3DC914jn4PTA%40mail.gmail.com.

[Tom Goreau]

We have YET to see sudden increase in sea level rise, but there is clear evidence of it in the past, when many inhabited coastal areas were flooded in the early Holocene.

 

The submerged Indus Valley civilization ruins off the coast of Gujarat might have been submerged by a later earthquake rather than ice cap melt. They are so buried in mud that real excavation is impossible.

 

When sudden sea level rise REALLY begins, it will be undeniable except to fools.

 

We may get a first little taste of it this year, when the El Niño just starting raises Pacific sea levels, causing more more islands to flood.

 

From: healthy-planet-...@googlegroups.com <healthy-planet-...@googlegroups.com> on behalf of John Nissen <johnnis...@gmail.com>

Date: Friday, May 15, 2026 at 15:59
To: Alan Kerstein <alan.k...@gmail.com>
Cc: Veli Albert Kallio <albert...@hotmail.com>, Peter Wadhams <peter....@gmail.com>, Planetary Restoration <planetary-...@googlegroups.com>, healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>, JOHN ENGLANDER <johneng...@gmail.com>, Oren Gruenbaum <oren.gr...@theguardian.com>

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[Michael MacCracken]

Hi Ron--Yes, thank you for the correction.

Mike

[John Nissen]

Hi Bruce,

The 0.2m in 15 years is obviously wrong.  But SLR has been underestimated according to recent research.  I would look at the graph in [1] and you can see an acceleration: the rate of SLR has been increasing, so the slope is getting steeper.  The SLR from 1900 to 1980 was 0.1m and from 1980 to 2015 a further 0.1m in less than a half of the time.  With a rate of 0.4mm per year since then, the current level should be around 0.25m above the 1900 level.  

The rate is roughly proportional to the global temperature* for steric SLR.  On current trends, the global temperature will reach 4C by 2100, from 1.5C in 2025.  That's a forecast rise of 2.5C in 75 years, giving an average global temperature* of 2.75C.  We might expect, for example, an average of 0.6mm per year of steric SLR from 2025 to 2100, giving us 0.45m on top of the 0.25 SLR at present.

That is bad enough, but the real danger and high risk comes from a partial collapse of the Greenland Ice Sheet, triggering gigatsunamis. sudden SLR, and a partial collapse of some large Antarctic glaciers to add to the SLR from the GIS. 

Cheers, John

* Global temperatures are relative to the IPCC's original 1900 baseline.

[1] https://www.eea.europa.eu/en/analysis/indicators/global-and-european-sea-level-rise/observed-and-projected-change

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