World Temperature Forecaster

[Robert Chris]

Hi All

Introduction to World Temperature Forecaster (WTF)

To supplement Bruce’s model, I have adapted the FaIR model developed by climate scientists and used by IPCC in AR6.  WTF runs in Excel.  The core computations that generate the forecasts are unchanged from those used in FaIR v2.0.0 

The adaptations make the FaIR model accessible to users without postgraduate degrees in climate science by considerably simplifying the input requirements and by enhancing the graphical outputs to focus more sharply on the key factors that affect climate policy.

WTF produces forecasts for high, medium and low emissions SSP scenarios that for practical purposes are the same as those generated by FaIR.  This is despite WTF treating all the non-CO₂ greenhouse gases as a single source of warming equivalent to a fixed percentage of that produced by CO₂.  This allows annual CO₂ emissions, CDR and SRM to be specified from 2025 to 2300 by only six or seven inputs each.  

If trying to find a scenario to deliver a desired forecast temperature profile, users can refine scenarios by changing any single input variable.  WTF runs virtually instantaneously allowing rapid exploration of a wide range of scenarios.

The purpose of adapting an academically and institutionally recognised Simple Climate Model for lay use is to enable anyone with access to Excel to examine for themselves the impact of any policy scenario enabling them better to understand the likely impacts of both national and international climate policies, and to know that that understanding is based on credible forecasts.

WTF is designed to be easy to use.  It is hoped that new users will require less than 30 minutes to engage with it and run their first few policy scenarios.  The following steps are recommended.

1. Using this link, download the two files WTF v1.0.0.xlsx and WTF – Introduction v1.0.0.pdf.
2. Read the first two pages of the PDF document and briefly peruse the other pages containing scenarios that could be used to get started.
3. Save a back-up copy of the Excel file before you make any changes.  This can be restored if either you want to revert to the default scenario, or your working version becomes unusable for any reason.
4. Open the Excel file and open the WTF tab. 

There are 35 worksheets in the model.  All but three of them are hidden.

The Corrob tab shows the degree of agreement between FaIR v2.0.0 and WTF v1.0.0 for four different SSP scenarios.  Users do not need to engage with this tab, other than to draw some comfort from the minimal differences between the two.

The hidden tabs can be unhidden for those interested in delving into the minutiae of the model.  There are no passwords.  The Excel file is more than 12MB because it contains a vast amount of historical and SSP data from 1750 to 2300.  Only a small portion of this is used by WTF but it has been left in this prototype version of WTF so that anyone wishing to access it can do so.  For those interested in looking at the original FaIR v2.0.0 model, you are referred to 1 (below) where you will find links to a full range of resources.

On the WTF tab, all but the green cells (and Cell B22 that allows users to set a desired safe temperature threshold) are locked to prevent inadvertent changes.  There are no passwords to unlock the locked cells.  However, the inputs in the locked cells are required for functions that have not yet been fully tested (e.g. different values of Equilibrium Climate Sensitivity (ECS), changes to the emissions and removal of methane and other Short Lived Climate Pollutants (SLCPs), so they should be used with caution.

It should be noted that the formulae at the heart of FaIR and WTF refer to global values.  These models cannot be used to assess regional climate impacts.

It is also important to note that these models offer no insights into how any scenario is to be delivered.  Inputs are stated in units of GtCO2 for annual CO2 emissions and CDR, and Wm-2 for SRM.  How policymakers propose delivering emissions reductions, CDR or SRM is a question that should be asked once it is clear how much of each is needed over what timescale.

WTF v1.0.0 is a work in progress.  All feedback will be welcome.

Dr. Robert Chris

robert...@gmail.com

 

1.           Leach, N. J. et al. FaIRv2.0.0: a generalized impulse response model for climate uncertainty and future scenario exploration. Geosci. Model Dev. 14, 3007–3036 (2021).

 

Regards

Robert

[Robert Chris]

Further to my message below, I should have suggested that when you open the Excel WTF file for the first time and open the WTF tab, you spend a few minutes getting to grips with the scenario presented.  It's one that mixes emissions reductions, CDR and SRM so that warming peaks at 1.7^oC around mid-century and then stabilises at around 1^oC.

Look at the inputs in the green cells and see how these are reflected in the charts showing emissions, warming, forcing and CO₂ ppm.  You can make your own judgement as to whether this scenario is feasible.  This should help you construct other scenarios you might want to investigate.

Also note that you must download the file, it won't run in the cloud.  

Regards

Robert

---

From: Robert Chris <robert...@gmail.com>
Sent: Saturday, October 25, 2025 15:01
To: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>
Subject: World Temperature Forecaster

[Robert Chris]

Hi Mike & Oswald

I suspect you are both interested in what WTF says about methane.  So here's something to get your teeth into.

WTF bundles all non-CO2 GHGs together and treats them as a single forcing agent.  I have shown that for four SSP scenarios this makes virtually no difference to either temperature or concentration outcomes.  But doing this doesn't allow an analysis of any individual GHG within that bundle.

I wanted to see how much difference methane makes within the native FaIR model (i.e. not my WTF version) so I ran four different SSP scenarios (high, medium, low and mixed emissions) with unmitigated methane, methane emissions halved from 2030 and methane emissions completely eliminated from 2030.  Here are the results.

	Warming oC						Concentration ppb
	CH4 unmitigated		CH4 emissions halved >2030		No CH4 emissions after 2030		CH4 unmitigated		CH4 emissions halved >2030		No CH4 emissions after 2030
SSP	2050	2100	2050	2100	2050	2100	2050	2100	2050	2100	2050	2100
119	1.66	1.43	1.57	1.36	1.49	1.28	1254.24	1005.65	1017.09	860.58	788.82	720.12
245	2.14	2.84	1.98	2.66	1.81	2.47	1804.65	1524.64	1287.26	1105.77	806.30	720.12
370	2.30	4.05	2.09	3.63	1.85	3.20	2309.19	3051.34	1527.41	1760.77	816.75	720.13
585	2.65	4.92	2.43	4.61	2.19	4.29	2363.81	2155.62	1549.24	1376.87	810.45	720.10

The key points to note here are that the change in temperature and concentration for each SSP is linear with the degree of emissions reduction and that with 100% mitigation (i.e. no methane emissions after 2030) the concentration falls back to pre-industrial by 2100 and is very little above it as quickly as 2050.   In all cases the temperature reduction by 2100 increases from ~0.3 to ~0.6^oC in relation to the level of emissions in the scenario, and commensurately less by 2050.

Do these results fit with your expectations?

Regards

Robert

---

From: Robert Chris <robert...@gmail.com>

Sent: Saturday, October 25, 2025 15:01
To: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>
Subject: World Temperature Forecaster

[Michael MacCracken]

Hi Robert--I'm tied up with another activity so can't look deeply into this, but it sounds plausible. Have you compared it to results that Drew Shindell et al reported in their UNEP study and then in an article in Science (copies attached).

I'd note that tropospheric ozone also has short lifetime (weeks) and black carbon as well, so it is not just counting methane using GWP-100 that is a problem in considering just CO2e (with GWP+100).

Best, Mike

[Robert Chris]

Hi Mike

Thanks for that reference.  I'm afraid that I read these worthy reports with a rather jaundiced eye.  They're full of lines like 'The full implementation of the selected measures by 2030 leads to significant...' followed by whatever benefits they're pushing.  These reports are important because they are like drips that slowly accumulate, eventually to wear a channel through the rocks onto which they're falling.  But it's slow, very slow.  Too slow.

What is needed is a sense of urgency and sadly more reports like this from UN agencies and prestigious academic institutions are just not cutting that pathway quickly enough.

The reality is that the best way to reduce most SLCPs is to reduce hydrocarbon combustion (whether fossil or organic).  That's why in the models setting the non-CO2 forcing as a fixed percentage of CO2 forcing produces results that are hardly distinguishable from those where each of the dozens of other GHG species are considered on their own individual merits.

Moreover, it's one thing to note that most SLCPs would yield to existing practices if they were scaled up, but the practical realities of delivering that scale are by and large totally unrealistic.  If they were to happen, there certainly wouldn't be 'full implementation by 2030'.

That said, I'm not arguing that these things should be ignored.  Certainly go for the low hanging fruit but don't bank on doing much more in a climate change relevant timescale.

Regards

Robert

---

From: Michael MacCracken <mmac...@comcast.net>
Sent: 28 October 2025 19:25
To: Robert Chris <robert...@gmail.com>; oswald. petersen <oswald....@hispeed.ch>
Cc: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>
Subject: Re: World Temperature Forecaster

 

[Michael MacCracken]

Hi Robert--Just to note that the UNEP report goes back to 2010 or a bit before--so, when they wrote them, they made sense. I was sending them along to give a sense of the magnitude of the response--so several tenths of a degree and without complete elimination of all methane emissions--so should not complete removal  been more?

Mike

[oswald....@hispeed.ch]

Hi Robert,

 

methane is responsible for 0.5 °C of warming, and reducing it to pre-industrial would eliminate this warming.

 

Regards

 

Oswald

 

 

Von: 'Michael MacCracken' via Healthy Planet Action Coalition (HPAC) <healthy-planet-...@googlegroups.com>

Gesendet: Dienstag, 28. Oktober 2025 20:25
An: Robert Chris <robert...@gmail.com>; oswald. petersen <oswald....@hispeed.ch>
Cc: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>

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