Re: [HPAC] Fwd: Warming of 1.5°C is Too High for Polar Ice Sheets | Jan Umsonst

[John Nissen]

Thanks Ron,

This paper is one of the most realistic and down-to-earth I have read recently.  It is a step in the right direction.  It argues that we need to get the global temperature back below 1.0C, or possibly lower, if we are to prevent catastrophic sea level rise from the polar ice sheets.  Our group, PRAG, goes further and argues that the most urgent action is preventing the partial collapse of the Greenland Ice Sheet (GIS), which is in accelerated decline.  We want both the Arctic and global temperatures to be brought back to what they were around 1980 or earlier. The abstract of the paper, see below, points out this acceleration: a quadrupling of ice mass loss since the 90s.  Though the paper argues for more research, what they are saying seems a very good argument for cooling intervention to lower temperatures.  We add specific urgency: the GIS intervention needs to be before things get much worse and the point of no return is reached when even the most powerful cooling intervention is unable to prevent the slide towards collapse and metres of sea level rise. The urgency would justify the ambitious target of five years to ramp up SAI to full strength: where "full strength" means enough cooling power to start lowering the Arctic temperature and reversing the mass loss of the GIS.

BTW, the other four tipping processes in the Arctic might be saved from becoming irreversible by lowering the Arctic temperature; see the Arctic Emergency Report Card in draft.

Cheers, John

https://www.nature.com/articles/s43247-025-02299-w

Abstract

Mass loss from ice sheets in Greenland and Antarctica has quadrupled since the 1990s and now represents the dominant source of global mean sea-level rise from the cryosphere. This has raised concerns about their future stability and focussed attention on the global mean temperature thresholds that might trigger more rapid retreat or even collapse, with renewed calls to meet the more ambitious target of the Paris Climate Agreement and limit warming to +1.5 °C above pre-industrial. Here we synthesise multiple lines of evidence to show that +1.5 °C is too high and that even current climate forcing (+1.2 °C), if sustained, is likely to generate several metres of sea-level rise over the coming centuries, causing extensive loss and damage to coastal populations and challenging the implementation of adaptation measures. To avoid this requires a global mean temperature that is cooler than present and which we hypothesise to be closer to +1 °C above pre-industrial, possibly even lower, but further work is urgently required to more precisely determine a ‘safe limit’ for ice sheets.

On Sun, Nov 16, 2025 at 7:03 PM Ron Baiman <rpba...@gmail.com> wrote:

Thank you Barbara!

This appears to be a talk on this paper:

https://www.nature.com/articles/s43247-025-02299-w

(that has I recalled been previously shared on HPAC list - but good to get the COP30 talk on this!)

Best,

Ron 

Sent from my iPhone

Begin forwarded message:

From: Barbara Sneath <bjsn...@meer.org>
Date: November 15, 2025 at 12:08:34 PM CST
To: Ron Baiman <rpba...@gmail.com>
Subject: Warming of 1.5°C is Too High for Polar Ice Sheets | Jan Umsonst



Dear Ron,

Additional scientific evidence that GMST rise must be below 1 degrees C.  HPAC may wish to add this COP30 presentation to the website. 

Best wishes,

Barbara 

https://www.linkedin.com/posts/jan-umsonst-92ba859a_warming-of-15c-is-too-high-for-polar-ice-activity-7395414456786243584-bcWY?utm_source=share&utm_medium=member_ios&rcm=ACoAADTeOCoBnIUeNHsMIsJPhEutAmXRssnxKNQ

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[Tom Goreau]

We pointed out in 1990 that 1 degree C was too high for corals (attached) but nobody gave a rat’s ass! Hasn’t changed since.

 

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