Present level of greenhouse gases is enough for an ice-free planet

[David Spratt]

This is an amazing post, that shows that present level of greenhouse gases is enough for an ice-free planet.  No better argument for climate interventions!

https://justdean.substack.com/p/human-caused-climate-change-is-unmistakably

A great piece of science communication.

David

[rob...@rtulip.net]

Hi David, thank you very much for sharing this article by Dean Sovang.  It quantifies Hansen’s analysis of climate sensitivity with paleo data showing that doubling of CO2 eventually produces 9°C of warming.

 

People should study this chart to understand the “warming gap”, showing the future impact of committed warming from past emissions.  Climate sensitivity is shown by the gap between the industrial warming since 1850 and Earth’s natural climate variability.  The modern trajectory is steadily departing from the equilibrium curve.  That indicates an emerging seismic type of pressure whereby the temperature could suddenly rise sharply to match the underlying natural equilibrium.

 

I do however have to challenge one aspect of the article, its total failure to discuss albedo.  When David says “No better argument for climate interventions!” it is essential to note that the article totally fails to argue for climate interventions.  A “better argument” is one that actually argues the case rather than ignoring it.

 

Here are the mistakes.

 

Dean claims “The destination on the curve is determined by the CO₂ concentration at which the system eventually stabilizes — which is precisely why the timing of net-zero matters so profoundly.”  The mistake is in Dean’s term “precisely”, which assumes no human power can adjust the temperature curve with sunlight reflection.  Since geoengineering is possible, the claim about timing of net zero is false.  Net zero can readily be delayed if we manage heat.  The real main reason why the timing of net zero matters is ocean acidification and related destabilisation of biological systems.

 

Dean claims “At any given CO₂ concentration, the [warming] gap keeps growing as CO₂ rises faster than temperature can follow. The only way to stop that gap from growing is to reach net-zero CO₂ emissions.”  This is incorrect, as it assumes no albedo action to reflect sunlight.  Restoring albedo can reduce temperature.  Reaching net zero is not “only way to stop that gap from growing”.  In fact, sunlight reflection is far more feasible.  The net zero ambition is a far more difficult, slow, expensive, contested, dubious and risky strategy than solar geoengineering. Net zero simply does not operate at climate scale, in view of the emerging impacts of tipping points that will swamp all carbon efforts in the absence of higher albedo.  Seeing this requires looking beyond the climate bubble and beyond the lobbying against geoengineering to see that the mainstream fossil economy is almost totally opposed to decarbonisation except as a public relations exercise.  Net zero could be achieved by carbon mining, but this will be slow.  Decarbonising the economy is marginal to climate impacts.  Net zero will take far longer than is needed to close the warming gap, which can only be achieved by sunlight reflection and related technologies.

 

Regards

 

Robert Tulip

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[PR CARTER]

One feedback, the 'albedo flip' property of ice/water, provides a powerful trigger mechanism. A climate forcing that 'flips' the albedo of a sufficient portion of an ice sheet can spark a cataclysm. 

2007, Climate change and trace gases, James Hansen  et al

Thanks David 

Peter C

---

From: "Robert Tulip" <rob...@rtulip.net>
To: "David Spratt" <dsp...@bigpond.net.au>, "healthy-planet-action-coalition" <healthy-planet-...@googlegroups.com>
Sent: Tuesday, April 7, 2026 7:13:07 PM
Subject: RE: [HPAC] Present level of greenhouse gases is enough for an ice-free planet

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--

Director Climate Emergency Institute
IPCC expert reviewer
Co-author2018 Unprecedented Crime: Climate Science Denial and Game Changers for Survival

[Tom Goreau]

The first paper to present this graph pointed out the large discrepancy between paleoclimate sensitivity (slope of curve) and that estimated by models was due to long lived positive feedbacks not included in climate models (attached).

 

From: healthy-planet-...@googlegroups.com <healthy-planet-...@googlegroups.com> on behalf of rob...@rtulip.net <rob...@rtulip.net>
Date:

Tuesday, April 7, 2026 at 22:13

To: 'David Spratt' <dsp...@bigpond.net.au>, 'healthy-planet-action-coalition' <healthy-planet-...@googlegroups.com>

.
To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/014a01dcc6fd%243f7833e0%24be689ba0%24%40rtulip.net.

[David Price]

Yes exactly! The time scales for some of those feedback effects to fully stabilize—to create a quasi-equilibrated global climate — are likely 2 or 3 orders of magnitude longer than what is considered by the GCMs.

It seems to me most people do not want to consider the implications of Hansen et al’s analysis: For atmospheric CO2 at present-day levels…. or for 2X pre-industrial, we have to go back 10s of millions of years to find a truly “equilibrated climate” — several degrees C warmer than today’s. 

The biosphere is simply not equipped to return CO2 concentration to ~300 ppm in a few decades or even centuries: maybe in tens to hundreds of millennia: the evidence for this lies in the paleo record.

David 

From my cellphone

I acknowledge that I reside on unceded Traditional Territory of the Secwépemc People

On Apr 8, 2026, at 3:25 am, Tom Goreau <gor...@globalcoral.org> wrote:



To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/BY3PR13MB49945F040741C2E31EF037D7DD5BA%40BY3PR13MB4994.namprd13.prod.outlook.com.

<Balancing Atmospheric Carbon Dioxide.pdf>

[PR CARTER]

Right. 

Emily Judd said we are heating Earth much faster than in the past half billion years- that was before the recent acceleration

Best regards

Peter C

---

From: "David Price" <da...@pricenet.ca>
To: "Thomas Goreau" <gor...@globalcoral.org>
Cc: "Robert Tulip" <rob...@rtulip.net>, "David Spratt" <dsp...@bigpond.net.au>, "healthy-planet-action-coalition" <healthy-planet-...@googlegroups.com>
Sent: Wednesday, April 8, 2026 10:40:31 AM
Subject: Re: [HPAC] Present level of greenhouse gases is enough for an ice-free planet

To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/5FB132FF-54E4-4C17-88AC-F25F921970C1%40pricenet.ca.

[John Nissen]

Hi Robert and David,

I have major doubts about the climate sensitivity approach. The paleo record is not always clear whether a CO2 increase or decrease is the cause of temperature change or the result of temperature change.  In the case of Pinubo, the CO2 decrease was almost certainly the result of temperature decrease.  Land and oceans have been absorbing respectively 1/6 and 1/3 of our emissions (10 GtC per year).  As temperature rises, they can absorb less.  I have not seen estimates of how much less; but it used to be said that land and oceans would cease to be absorbers at around 2C of global warming.  At any rate, a CO2 increase will result from heating.  Thus the equilibrium curves in Figure 1 are suspect IMHO.

This aside, there is a glaring error in Figure 2, where the projection in red takes us to 2100.  There should be a much steeper line from 2025, as the trend is to 4C by 2100.  And 2C is almost certain by 2040, since current warming is 0.35C or 0.36C per decade according to recent estimates.

So clearly emissions reduction and the achievement of net zero, even before 2050, is not enough to prevent tipping point catastrophe.  

Consider sea level rise (SLR).  One tipping element is the Greenland Ice Sheet.  As Mike points out, the paleo history points to 15m of SLR per degree C, which means the equilibrium sea level for 4C is 60m: most of the Greenland ice would be gone!  Our only chance of halting the Arctic meltdown and reducing tipping point catastrophe is by rapid deployment of the most powerful cooling intervention available, namely SAI.  A similar intervention may also be needed in the Antarctic and more generally for the cryosphere elsewhere through global cooling.

Cheers, John

To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/014a01dcc6fd%243f7833e0%24be689ba0%24%40rtulip.net.

[Tom Goreau]

Two comments:

 

Temperature and CO2 and sea level covary so strongly because they are tightly linked by feedbacks, which are included in paleoclimate sensitivity estimates, but largely lacking, and significantly underestimated, in climate change models. Cause and effect (CO2 vs T vs SLR) cannot be simply separated.

 

60 metres of sea level rise does not leave ANY ice in Greenland, in fact it means melting almost all of Antarctica as well! That’s the longest delayed positive feedback in the climate system other than crustal isostatic readjustment (which it mostly causes).

 

To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/CACS_FxrmyrxdoSBKCSYrq9ocOJGYULO35kCtSzLGD5O6JqvekQ%40mail.gmail.com.

[Tom Goreau]

To clarify, isostatic feedback can function as a delayed thousands of years negative or positive feedback during different parts of the glaciation/deglaciation cycle.

 

To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/SA1PR13MB5005432B3B841845B844C334DD592%40SA1PR13MB5005.namprd13.prod.outlook.com.

[David Spratt]

The red line is presumably IPCC and/or CMIP6 projections, of around 3C by 2100, which is likely too low, but then again when you have four scenarios to chose from, you can can up with whatever figure you wish!  It represent what policymakers believe, and I think that is the point!

But this does not take away from the basic point, which is very clear and strong, that there is a world of difference between projections based on short-term and low climate sensitivity, compared to the reality at equilibrium over hundreds to possibly thousands of years when all feedbacks have worked their way through the system, using the paleoclimate record. 

As to the relationship between CO2 and T and cause and effect, that is irrelevant.  It is always a dance,  is a rubber band between the two, always. A change in solar incoming solar radiation (Milankovitch cycles) cause increased T; that then releases CO2 from various carbon stores; which adds more T; and so on. That is the only way it can work through the ice/interglacial cycle!  The fact that various carbon stores and sources vary in their efficiency is irrelevant to the picture which the paleo data describes.  And of course the physical relationship between CO2 and T is not linear, as the diagram illustrates.  

But none of this takes away from the power of that diagram, which I find a very powerful example of good, accessible climate communication.

David Spratt

On 10 Apr 2026, at 10:25 pm, John Nissen <johnnis...@gmail.com> wrote:

Hi Robert and David,

I have major doubts about the climate sensitivity approach. The paleo record is not always clear whether a CO2 increase or decrease is the cause of temperature change or the result of temperature change.  In the case of Pinubo, the CO2 decrease was almost certainly the result of temperature decrease.  Land and oceans have been absorbing respectively 1/6 and 1/3 of our emissions (10 GtC per year).  As temperature rises, they can absorb less.  I have not seen estimates of how much less; but it used to be said that land and oceans would cease to be absorbers at around 2C of global warming.  At any rate, a CO2 increase will result from heating.  Thus the equilibrium curves in Figure 1 are suspect IMHO.

This aside, there is a glaring error in Figure 2, where the projection in red takes us to 2100.  There should be a much steeper line from 2025, as the trend is to 4C by 2100.  And 2C is almost certain by 2040, since current warming is 0.35C or 0.36C per decade according to recent estimates.

So clearly emissions reduction and the achievement of net zero, even before 2050, is not enough to prevent tipping point catastrophe.  

Consider sea level rise (SLR).  One tipping element is the Greenland Ice Sheet.  As Mike points out, the paleo history points to 15m of SLR per degree C, which means the equilibrium sea level for 4C is 60m: most of the Greenland ice would be gone!  Our only chance of halting the Arctic meltdown and reducing tipping point catastrophe is by rapid deployment of the most powerful cooling intervention available, namely SAI.  A similar intervention may also be needed in the Antarctic and more generally for the cryosphere elsewhere through global cooling.

Cheers, John

On Wed, Apr 8, 2026 at 3:13 AM <rob...@rtulip.net> wrote:

<image001.png>Hi David, thank you very much for sharing this article by Dean Sovang.  It quantifies Hansen’s analysis of climate sensitivity with paleo data showing that doubling of CO2 eventually produces 9°C of warming.

 

People should study this chart to understand the “warming gap”, showing the future impact of committed warming from past emissions.  Climate sensitivity is shown by the gap between the industrial warming since 1850 and Earth’s natural climate variability.  The modern trajectory is steadily departing from the equilibrium curve.  That indicates an emerging seismic type of pressure whereby the temperature could suddenly rise sharply to match the underlying natural equilibrium.

 

I do however have to challenge one aspect of the article, its total failure to discuss albedo.  When David says “No better argument for climate interventions!” it is essential to note that the article totally fails to argue for climate interventions.  A “better argument” is one that actually argues the case rather than ignoring it.

 

Here are the mistakes.

 

Dean claims “The destination on the curve is determined by the CO₂ concentration at which the system eventually stabilizes — which is precisely why the timing of net-zero matters so profoundly.”  The mistake is in Dean’s term “precisely”, which assumes no human power can adjust the temperature curve with sunlight reflection.  Since geoengineering is possible, the claim about timing of net zero is false.  Net zero can readily be delayed if we manage heat.  The real main reason why the timing of net zero matters is ocean acidification and related destabilisation of biological systems.

 

Dean claims “At any given CO₂ concentration, the [warming] gap keeps growing as CO₂ rises faster than temperature can follow. The only way to stop that gap from growing is to reach net-zero CO₂ emissions.”  This is incorrect, as it assumes no albedo action to reflect sunlight.  Restoring albedo can reduce temperature.  Reaching net zero is not “only way to stop that gap from growing”.  In fact, sunlight reflection is far more feasible.  The net zero ambition is a far more difficult, slow, expensive, contested, dubious and risky strategy than solar geoengineering. Net zero simply does not operate at climate scale, in view of the emerging impacts of tipping points that will swamp all carbon efforts in the absence of higher albedo.  Seeing this requires looking beyond the climate bubble and beyond the lobbying against geoengineering to see that the mainstream fossil economy is almost totally opposed to decarbonisation except as a public relations exercise.  Net zero could be achieved by carbon mining, but this will be slow.  Decarbonising the economy is marginal to climate impacts.  Net zero will take far longer than is needed to close the warming gap, which can only be achieved by sunlight reflection and related technologies.

 

Regards

 

Robert Tulip

 

 

From: 'David Spratt' via Healthy Planet Action Coalition (HPAC) <healthy-planet-...@googlegroups.com>
Sent: Wednesday, 8 April 2026 8:12 AM
To: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>
Subject: [HPAC] Present level of greenhouse gases is enough for an ice-free planet

 

This is an amazing post, that shows that present level of greenhouse gases is enough for an ice-free planet.  No better argument for climate interventions!

 

https://justdean.substack.com/p/human-caused-climate-change-is-unmistakably

 

A great piece of science communication.

 

David

 

 

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[Tom Harris]

Hi,

I've just published a longer explanation of Dean's diagram together with implications for CDR and net-zero. 

https://drtomharris.substack.com/p/the-anthropocene-hinge-point

Tom