Why delaying climate action now means higher seas by 2100

[John Nissen]

Hi all,

They make an interesting distinction between SLR from glaciers and from ice sheets. Slowing glaciers cannot be as effective as refreezing ice sheet surfaces and adding snow to redress the mass loss/gain balance.  SAI can help with the former, but increasing snowfall, especially over Greenland in winter, could be crucial: nobody is talking about this so we should!

BTW emissions reduction can make hardly any differences to the SLR situation, despite what they might say.  Without intervention we are on course for several metres of SLR by 2100 and possibly 1m by 2050.

Cheers John 

Why delaying climate action now means higher seas by 2100 – new research https://share.google/28vEUwVcgKhuZ2GqK 

[bruceh...@yahoo.com]

For planning purposed it would be helpful to know the expected sea level rise for various temperature increases.  Here is a set from EN-ROADS:

 

 

Once an agreement is reached for the maximum desired SLR in 2100 we would then know upper limit for the temperature increase.

 

Cheers!

 

Bruce Parker

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[John Nissen]

Hi Bruce,

That is very interesting, because it shows what the model indicates for sea level rise (SLR).  I have heard that the SLR between 2000 and 2025 has been underestimated and it should be 0.25m, not the 0.1m shown in the diagram on the right.  I believe the model is only modelling steric SLR, i.e the result of ocean expansion.  SLR from ice melt cannot be modelled because it is unpredictable.  But by 2100 there is likely to be an added contribution of at least a metre from ice melt.  The Arctic is already in meltdown, and several large Antarctic glaciers have become unstable.

The graph on the left begins at too low an angle: the current slope/rate is 0.35 or 0.36 degrees C per decade, according to two estimates.  With a straight line (i.e. at a constant rate without any acceleration in global warming) the global temperature will reach 4C by 2100.  

With 4C by 2100 and 0.25m already since 2000 and we get almost exactly 1m steric SLR by 2100.  Add in the melting ice we are likely to get a total of over 2m by 2100.

I've used these figures in submissions to the EU (on Arctic policy) and the UK (on security).  In a published letter to the FT I used cost estimates from a recent paper (suggested by John Moore) indicating a global cost of $700 billion per year for a SLR of 1 metre, and I used a cost estimate for SAI to avoid this SLR of around $11 billion per year.  SAI is extremely cost-effective, providing side-effects are manageable, which Doug MarMartin's research suggests they are. 

We should really be concentrating on the short tail of the probability distribution for our risk assessment.  There may be a small probability of a partial collapse of the Greenland Ice Sheet before 2040, but the impact would be huge.  The risk, as the product of probability and impact, would therefore be high, and far higher than the risk from deployment of SAI, ramped up carefully over the next few years. 

So the "climate action" which should not be delayed (see subject headline) is the deployment of SAI!

Cheers, John

[John Nissen]

Hi Joshua,

I have just seen what you posted on LinkedIn:

Last week the Council of the EU expressed its support for “a moratorium on deployment of SRM technologies.”  To be clear, this is a political pronouncement rather than a legal decree, and it is very much in line with the EU’s overall skeptical position regarding SRM.  A moratorium is a temporary prohibition or pause on some activity, not a ban, and if it were designed well, e.g., by tying it to expanded research, a moratorium could be a constructive step forward in geoengineering governance.  This was a key recommendation of the Climate Overshoot Commission (for which I worked) and I think deserves more attention as a governance proposal than it has received up to now.

The EU needs to be made aware of the danger from delaying deployment of SRM, and specifically SAI: to lower the Arctic temperature, halt Greenland meltdown, slow the release of methane from thawing permafrost, re-energise the polar jet stream to reduce its sticking and meandering behaviour, and keep the AMOC going.

Sea level rise (see my email below) should be of particular concern to the EU, with so much low-lying land.  I wrote to the EU concerning their policy on the Arctic (see attached), pointing out the dire situation in particular about SLR, and advocating that they take a lead on SAI, at least for its governance.  Thus their current attitude against SRM has to change.  Is there any chance of you promoting this much needed change in attitude?  We are in a planetary emergency due to polar meltdown, and they have not a clue about it.

Cheers, John

John Nissen

Chair of the Planetary Restoration Action Group

[bruceh...@yahoo.com]

Hi John –

 

Thanks for your comments.  As you noticed, the EN-ROADs model seems to be “out of date” with respect to SLR.  How can we get similar graphs based on the latest climate models? (The results should include the latest observations as described in “Sea level much higher than assumed in most coastal hazard assessments“ (https://www.nature.com/articles/s41586-026-10196-1). The article that you mentioned (“Why delaying climate action now means higher seas by 2100”) simply stated the obvious.  If we want policy makers to actually do something about SLR, we need to

1. Agree on the maximum desired SLR in 2100
2. Have graphs like the ones I created, but based on the output of complex climate models.

 

We would then be in a better position to say “Current climate model projections indicate that avoiding the maximum desired SLR in 2100 requires limiting global warming to below approximately X °C by mid-century and Y °C by 2100. Given present greenhouse gas emission trajectories—including both human sources and climate feedbacks—and the economic and practical constraints on mitigation and carbon removal, achieving these thresholds without additional forms of climate intervention appears unlikely.”

 

Cheers!

 

Bruce

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