Why the IPCC focuses on the scenarios that it does

Originally tweeted by Roger Pielke Jr. (@RogerPielkeJr) on August 7, 2021.

🧵Some might be curious why the IPCC focuses on the scenarios that it does

After all these scenarios are the foundation of the entire report’s look to the future & assessment of possible impacts and the worth of different policy approaches . . .

The short answer is that the highest priority scenarios were selected for scientific purposes first & considerations of plausibility absent

Here is how the CMIP6 exercise justified its baseline (BAU/reference) scenarios

➡️science & unmitigated baseline

Decisions on what scenarios to prioritize were made in 2015/16 but build on earlier decisions of CMIP5, IPCC 2007 & SRES 2000 and even earlier

The IPCC AR6 report in 2021 is really an assessment based on scenarios that were determined to be most relevant as much as 20 years ago

We detail much of this history and its consequences for climate science in this epic paper:


It is more than a little silly to have a breathlessly-awaited, embargoed report presenting analysis of out-of-date scenarios, but here we are!

If you want a more readable, shorter version of the story you can read this:

The IPCC could have decided to re-evaluate scenarios for the AR6 based on plausibility

That would have meant discarding or deemphasizing work once labelled highest priority – hard to do give sunk resources, published papers, egos

It might have looked like this . . .

Reimagined CMIP6 scenario use

Where we are headed on current trends:

What the world might look like under more aggressive emissions reduction policies:
SSP2-2.6, SSP1-2.6

Exploratory (implausible what ifs):
SSP3-7.0, SSP1-1.9

Fanciful (to advance science):

This CMIP6 figure illustrates clearly why holding firmly on to 8.5 as a reference scenario vs 4.5 is appealing for purposes of advocacy/messaging


Originally tweeted by Roger Pielke Jr. (@RogerPielkeJr) on August 7, 2021.

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August 7, 2021 6:07 pm

The IPCC. needs continued funding, so of course they will panic monger. If the likely outcome is not much change,and whatever is likely is positive, the countries would be much less likely to fund the IPCC.

Reply to  Tom Halla
August 7, 2021 6:24 pm

Yes: Money for the scientists. Power for the politicians.
— both quickly becoming the corruptors of our freedom.

Carlo, Monte
August 7, 2021 6:14 pm

“Forcing pathway” — jargon at its finest.

August 7, 2021 6:17 pm

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David Blenkinsop
Reply to  Eben
August 7, 2021 7:21 pm

Well, really, it shouldn’t be Albert Einstein standing in front of that particular blackboard!

It’s possible, though, that some of the alarmist “scientists” fantasize themselves as being the “climate Einstein”?

Mike McMillan
Reply to  David Blenkinsop
August 7, 2021 10:18 pm

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mark from the midwest
August 7, 2021 6:35 pm

Politicians always look for a “call to action” even when there is no “action to call for.” It’s because they lack the courage to do nothing.

Reply to  mark from the midwest
August 7, 2021 8:02 pm

Politicians are like an engine without a load, racing away, generating hot air, making a lot of noise, not contributing an iota of useful work, self-starting, and no off-switch to be found.

Reply to  mark from the midwest
August 7, 2021 10:24 pm

They think that they have to be seen to be doing something about the problem, so they need a problem to do something about.

Bob boder
Reply to  mark from the midwest
August 8, 2021 4:51 am


Thats factually a brilliant statement!
Some what and why in one nice sentence.

Reply to  mark from the midwest
August 8, 2021 5:21 am

i think it’s more that real problems are so much more difficult to solve then imaginary problems.

have a great Sunday!
(it’s cold and wet here in Brazil)

john harmsworth
Reply to  Willem69
August 9, 2021 8:12 am

Without problems they have no purpose and therefore no power. So they create and build up and exaggerate problems.

bill Johnston
Reply to  mark from the midwest
August 8, 2021 9:11 am

It is also because they have to justify their lofty position.

oeman 50
Reply to  mark from the midwest
August 8, 2021 1:58 pm

It’s not just the run-of-the-mill politicians. It is also includes the bureaucracies created to handle problems. I’m thinking mainly of the EPA. Once the low hanging fruit is picked, they still have the resources and power to continue going after diminishing returns, requiring clean-up of ever smaller amounts of emissions, costing ever increasing amounts of money.

Jeffery P
Reply to  mark from the midwest
August 9, 2021 1:22 pm

How are they going to separate us from more of our money if they don’t come up with new (largely imaginary) problems and big-government programs to “solve” them?

We’d all been better off if response to the pandemic was limited in scope. But that doesn’t give politicians and bureaucrats more power. That doesn’t get them reelected. Unfortunately the American public demands big programs and they will give more campaign dollars if they believe they will get free stuff.

Gary Pearse
August 7, 2021 7:23 pm

Really, they can’t get beyond the Charney report of 1979 that wasn’t bad for the state of knowledge at the time. But to have not reduced the range of climate sensitivities in 30yrs, especially when 30yr old forecasts turned out to be 300% too warm compared to direct observations is scientific malpractice.

Dr. Pielke Jr. you are far too easy on the IPCC. They are not testing for science purposes. Your complaint that they are using 20yr old parameters is the simple evidence that science has nothing to do with it. They know and you even know that if they halve their 8.4 scenario AND reduce the ECS to the average of Charny’s range (still too high compared to recent estimations), then ‘business as usual’ would meet the Paris accord, the dismantling of our civilization would be stopped and the worlds citizens would share the abundance of a beautifully greened planet.

D Boss
Reply to  Gary Pearse
August 8, 2021 4:45 am

Precisely! We should not give one iota of credibility to them by writing that their “estimates” should be halved! We should instead point out that their record of predictions is abysmal, and they should be ridiculed, ostracized, pilloried and shamed for their non-science behavior.

The very same sorts of GCM models are used for Hurricane prediction, and those cannot be considered accurate more than 120 hours in the future! AND they start with actual measured parameters, not “tuned” gibberish. Therefore EVERYONE must scoff at the 20-100 year future mystical tarot card/chicken bone readings of the warmunists!

August 7, 2021 7:39 pm

In their first sentence of the abstract the start-off with backwards logic, and go down hill from there.

“Projections of future climate change play a fundamental role in improving understanding of the climate system…”

Science works the other way around.

Zig Zag Wanderer
Reply to  ThinAir
August 7, 2021 7:51 pm

Science works the other way around

That is entirely appropriate. After all, CO2 in the climate works completely the other way around to the way it works in Climate Scientology ™.

Jim Gorman
Reply to  ThinAir
August 8, 2021 4:53 am

Thin –> +100

“Projections of future climate change play a fundamental role in improving understanding of the climate system…”

This is exactly backwards as you say. Science is based on real, physical OBSERVATIONS. Hypothesis modification to make it agree with observations is the goal.

Climate scientists somehow have turned this around into saying hypothesis’ drive what is happening regardless of observations.

Funding is no longer based upon the process of matching observation to the hypothesis or it would only be awarding those who come closest to actual observation. Instead, funding is awarded based upon the worst outcomes that can can be used to drive fear.

August 7, 2021 9:32 pm

The link to the “epic paper” generates an error for me – seems to be something attached to the end of the URL.
Is it just me?

But this one works:


Malcolm Chapman
Reply to  Raven
August 8, 2021 5:01 am

Thanks, I had the same problem. I’ve got it now, albeit paywalled.

Chris Hanley
August 7, 2021 10:09 pm

Speculating on different emission ‘scenarios’ (RCPs) is a distraction from the fundamental problem.
The Indian in John Locke’s An Essay Concerning Human Understanding said the world was supported on an elephant which was on a tortoise “but being again pressed to know what gave support to the broad-backed tortoise, replied something, he knew not what” (Wiki).
Like some ancient mythology IPCC temperature prophecies are based on emission scenarios that are supported by a value that is unknown viz. climate sensitivity.

Reply to  Chris Hanley
August 7, 2021 10:28 pm

But it is worse than we thought. “Speculating on different emission ‘scenarios’ (RCPs) is a distraction from the fundamental problem” which is “does changing the concentration of CO2 in the atmosphere cause a climate change”?

Ed Hanley
Reply to  Chris Hanley
August 7, 2021 10:36 pm

It’s turtles all the way down. Now, for asking, you go to jail.

Peta of Newark
Reply to  Chris Hanley
August 7, 2021 10:52 pm

Quote:”Like some ancient mythology IPCC temperature prophecies are based on emission scenarios that are supported by a value that is unknown viz. climate sensitivity”

Let’s sort that:
“Like some belligerent fantasy IPCC temperature prophecies are based on an emissivity figure for CO2 scenario that are supported by a value that is known viz. zero to 3 decimal places

How on Earth do they get a figure of 8.5 Watt per square metre for ‘forcing’?

  • CO2 effectively does not radiate at atmospheric temps & pressures
  • Nothing nowhere in the atmosphere can ‘force’ anything below it because of Lapse Rate – cold objects do NOT ‘force’ warm ones

IOW They have built this huge House of Cards on something that is immeasurable – so what do Climate Models actually do, what are they working out?

It is asserted that CO2 is a ‘heat trapping gas’
Everything in this Universe ‘traps heat’ – it’s how the Universe works – cold objects absorb energy coming off warmer ones

Even before they make the huge unmeasured and never stated conversion from ‘heat’ to ‘temperature’

You can not do that: Temperature is a dimensionless number, it means nothing unless you define exactly what you are recording the temperature of.
In the special and present case of Earth’s atmosphere you must specify the water vapour content.

Yet they never do.
Just as they assume an emissivity figure of unity for everything, they assume the atmosphere never changes its composition and heat capacity.

While they do constantly rave about its ‘composition’ – saying that CO2 changes and that that alters the water content.
Is that what you call ‘Cognitive Dissonance’

Well Intentioned they are maybe but: These People are Fraudsters Cheats and Liars

Reply to  Peta of Newark
August 8, 2021 1:52 am

The honest truth – and they will never admit it – is they really have no idea at all.

If you don’t know how something works trying to model it is a total waste of time – and loadsa money

Reply to  Peta of Newark
August 8, 2021 7:01 am

Again I post the replicated experimental findings of Hoyt Hottel to emphasize what Peta says.
CO2 has near zero emissivity below 33C.

Mike McMillan
August 7, 2021 10:34 pm

Thermal conductivity of carbon is 1.7 watts/mK. I think that’s an R of 0.015, give or take a few decimal places, a little better than window glass, but not as transparent.

Joel O'Bryan
August 8, 2021 12:07 am

The 8.5 scenario was always intended as the Honey Pot trap to lure in diverse fields of scientists needed impact to get published. They use it and to show climate change effect in their research in areas affected by weather and climate … research that is based on a “publish or perish” paradigm.
The public is largely unaware of the massive scientific scam that is being foisted on them by corrupt climate scientists and the politicians who fund them.

Vincent Causey
August 8, 2021 12:13 am

Their reasoning can be paraphrased as, we used RCP8.5 because it is the only one that gives the outcome our masters desire.

August 8, 2021 12:50 am


Reply to  fretslider
August 8, 2021 1:22 am


Reply to  TheFinalNail
August 8, 2021 1:42 am


Does what it says on the tin.

Reply to  TheFinalNail
August 8, 2021 7:49 am

That’s why they write the summary for politicians before the individual chapters are finished. So that they summaries for the individual chapters can be adjusted to match the predetermined narrative.

Dave Fair
Reply to  fretslider
August 8, 2021 9:13 pm


Richard Page
August 8, 2021 9:38 am

No you actually aren’t. You’re broadcasting your own.

Smart Rock
August 8, 2021 10:02 am

highest priority scenarios were selected for scientific purposes first

That’s a very charitable conclusion. Of course, the thought that they might lead to exaggerated estimates of future warming that could be exploited by the bad news factory, would never have occurred to these dedicated, disinterested, remorselessly objective scientists in their ivory tower. Would it now?

My favourite illustration of disinterested science: “Once the rockets go up, who cares where they come down? That’s not my department, says Wernher Von Braun

Old Cocky
Reply to  Smart Rock
August 8, 2021 2:24 pm

It needs Tom Lehrer’s fake Cherman accent to give best effect 🙂

August 8, 2021 5:38 pm


I Prefer Cataclysmic Cases

Dave Fair
August 8, 2021 8:57 pm

How interesting that the UN IPCC CliSciFi models neck down during the the tuning period of the late 20th Century then diverge wildly in hindcast and forecast. I assume that the CliSciFi CMIP6 models still have a difference of 3 C in the average global temperatures. Water freezes at 3 C and boils at 97 C?

Reply to  Dave Fair
August 8, 2021 9:37 pm

That’s because the science is settled.

Jeffery P
August 9, 2021 1:15 pm

They focus on these scenarios to pump up the fear. People will cough up more tax dollars for a crisis. They might even be persuaded to endorse radical ideas, such as ending capitalism and adopting a global government. These are the actual goals of the climate change movement — Marxism and global governance by the self-appointed elites (that is, themselves).

Fear and crisis are the enemies of facts and reason. Panic makes people pliable to nonsensical ideas.

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