CMIP7 and WTF

[Robert Chris]

I have updated WTF  to include more recent emissions data, a routine to explore the impact of alternative values for ECS and a comparison with the temperature forecasts from the team generating scenarios for CMIP7.

I am particularly pleased with the chart below which shows the temperature chart from [1] (shaded ranges) overlaid with the corresponding scenarios (approximate) from WTF v1.0.9 (dashed lines). You can see a high degree of conformity.  On the one hand this is unsurprising because the chart from [1] is based on FaIR as is WTF.  However, it illustrates that the simplifications I have made to FaIR to make it accessible to ordinary mortals, makes little difference to the global temperature forecasts.

This exercise is also interesting because van Vuuren et al describe all their scenarios as being 'plausible'.  If the High emissions scenario which delivers warming of 3-4^oC by 2100 and around 5^oC by 2150 is plausible, it begs the questions a) do we care, and b) if we do, what is to be done to avert it?  Note that a legitimate answer to that question is not to ramp up renewables, accelerate the retirement of FF and the deployment of CDR because this scenario assumes that it is plausible those will not happen - they are provided for in the other scenarios.  The only legitimate responses are adapt to the warming as best we can and/or reduce absorbed solar radiation .

I think it's a slam dunk!

No one seems to have been interested in making use of WTF so I haven't bothered to update the shared version.  I'm happy to  make it available to anyone who's interested.

1.           Van Vuuren, D.P.; O’Neill, B.C.; Tebaldi, C.; Sanderson, B.M.; Chini, L.P.; Friedlingstein, P.; Hasegawa, T.; Riahi, K.; Govindasamy, B.; Bauer, N.; et al. The Scenario Model Intercomparison Project for CMIP7 (ScenarioMIP-CMIP7). Geosci. Model Dev. 2026, 19, 2627–2656, doi:10.5194/gmd-19-2627-2026.

Regards

RobertC

[John Nissen]

Hi Robert,

When the models are all wrong, then an analysis/synthesis of the models, as in your WTF chart, is going to be all wrong.  There is no way that emissions reduction can significantly alter the current trajectory, which, even without acceleration or tipping point amplification, is to 2C before 2040, 3C before 2070, and 4C before 2100.  That's the reason we are not interested in using the WTF: I'm sorry, Robert, after all your trouble.  

Of course, your conclusion is basically correct: we adapt to warming as best we can and/or reduce absorbed radiation.  This boils down to a policy choice:

EITHER we adapt to warming as best we can and accept the inevitability of tipping point catastrophes and the possibility of 4 billion dying as a result (as per Roger Hallam)

OR we quickly deploy SAI to lower temperatures everywhere but with a priority on the Arctic because of halting the critical tipping processes there, meanwhile adapting as best we can to changes in climate and sea level.

Only SAI has the necessary cooling power for lowering the Arctic temperature*.  But SAI should be backed up by other cooling methods, especially for refreezing the Arctic because of the cost of failure.

Massive CDR is necessary this century to bring down the level of CO2 in the atmosphere, and allow phasing out of SAI and any other SRM techniques by 2100 or preferably sooner.

Cheers, John

*As much as 0.5 petawatt of sustained cooling power may be necessary for lowering the Arctic temperature and allowing it to refreeze.

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[Robert Chris]

Hi John

Of course the models are wrong!  Everyone knows that.  But some are useful. (George Box)

If you want policymakers only to rely on what they know to be true, you're inviting total policy paralysis.   Almost all policy is conered with the future.  The truth about the future will not be available until it emerges by which time it'll be a bit late to intervene to change it.

Even with all their shortcomings, the models, including WTF, show that interventions in the carbon cycle are no longer sufficient.  Quite how insufficient is of little concern to me.  If you want to launch a debate about what level of fuckedness is acceptable, be my guest.

Regards

RobertC

[Robert Chris]

Typo: concerned

Sent from my Galaxy

[John Nissen]

Hi Robert,

We know enough about the current situation and trends that we can deduce the necessity for rapid SAI deployment.  Later will be too late!  It is now a matter of explaining this to people in authority who have hitherto put their faith in the pundits of climate change who say that emissions reduction is enough and SAI is too risky.  These people in authority (except in the US and Russia) are now beginning to feel, and publicly acknowledge, the effects of the crisis with heat domes, flooding, etc.  It is a good moment to press home our case for intervention and reassure them about SAI, thus overturning what they have been told by the pundits.

BTW, the finding that only SAI has the necessary cooling power for lowering the Arctic temperature is very recent; as is the finding that responsible SAI deployment could prove extremely benign.  Before then, MCB looked very hopeful; since then, MCB seems to have met one problem after another, including getting it to work.

Cheers, John

[rob...@rtulip.net]

I am very interested in using WTF.  It is the best source I have seen to analyse the required balance between SRM, GGR and emissions reduction.

 

WTF is a simple and accessible way to quantify projections for arguments such as John Nissen’s claim here that “Massive CDR is necessary this century to bring down the level of CO2 in the atmosphere, and allow phasing out of SAI and any other SRM techniques by 2100 or preferably sooner.”

 

I think it is most unlikely that SRM will be phased out in view of its immense weather optimisation benefits.  Rebrightening is ongoing necessary planetary infrastructure.

 

Regards

 

Robert Tulip

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