The Misuse of RCP4.5

Originally tweeted by The Honest Broker by Roger Pielke Jr. (@RogerPielkeJr) on April 25, 2023.

I talk a lot about RCP8.5, and rightly so

But there is another scenario that is just as widely misused, and that is RCP4.5

Let's talk a bit about RCP4.5 . . .

RCP4.5 is a scenario that includes climate policy which alters the world's trajectory from a 7.0 W/m^2 trajectory in the GCAM reference scenario

RCP4.5 is often (maybe even typically) paired with RCP8.5 to demonstrate climate policy success, with RCP8.5 used as a reference scenario (or, as they say, BAU)

A good example of this practice is the 2018 US National Climate Assessment

This is flawed for at least 3 reasons…

First, as you surely know by now, RCP8.5 is not an appropriate reference scenario for anything, so using that as a baseline for any purpose is methodological malpractice

Second, you cannot pair RCP8.5 and RCP4.5 and they are from different IAMs & represent very different worlds

The big one – if RCP4.5 is indeed to be viewed as climate policy success, then we can all go home as according to the UNFCCC the world is currently undershooting RCP4.5 as you can clearly see in figure below (which illustrates SSP2-4.5 trajectory)

So if you believe climate policy stops today then you can use RCP4.5 as an upper bound scenario (not as a stress test of course, a different discussion)

Don't just take it from me, the Biden administration's central SCC scenario undershoots RCP4.5 to 2100

Don't like Biden admin estimates?
Here is our assessment of plausible IPCC scenarios with SSP2-3.4 at the center and SSP2-4.5 as an upper bound

Why is RCP4.5 not a good proxy for climate policy success?

Well, according to IPCC AR6 it leads to a central estimate of 2.9C temperature change in 2100, which is not 2.0 or 1.5

So why is RCP4.5 frequently used to represent climate policy success & RCP8.5 used as a baseline, when both uses are scientifically unjustifiable?

Well, those are the scenarios that are readily available for research, so they get used even though the use is scientifically flawed

Google Scholar says there are 24,500 studies that pair RCP4.5 and RCP8.5 in research

Just look at the example titles below

To the extent that this research is supposed to say something about plausible futures, it is of little value to informing policy & may even mislead

So if you are a researcher and you think, "Hey, maybe I'll do a comparison of XYZ in RCP8.5 and compare it to RCP4.5 to illustrate the benefits of mitigation"

Just say no

And if you are a consumer of climate science in your research, as a reporter or in policy and you come across a study that compares the fictional world of RCP8.5 and the false world of RCP4.5 as mitigation success

Move along, nothing to see here

You want to do a proper study of the benefits of mitigation based on today's view of "current policy" trajectories?

Use RCP4.5 as an upper end and RCP3.4 (or 2.6) as your lower end to represent mitigation success

Guess how many studies exist that perform that analysis?

This thread will soon be a post at The Honest Broker, as nerdy as it is, it is a story needed to be told because the misuse of RCP4.5 – while not as flashy as RCP8.5 – is important and endemic

Comments welcome here

Post coming before long, don't miss it:

Originally tweeted by The Honest Broker by Roger Pielke Jr. (@RogerPielkeJr) on April 25, 2023.

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Henry Pool
April 26, 2023 10:45 pm
Bryan A
Reply to  Henry Pool
April 27, 2023 4:01 pm

The chart (figure 1.21) indicates a savings of about $75B per year with mitigation to lower the CO2 from RCP 8.5 to RCP 4.5
Just how many $Trillions per year will it cost to realize that $75B non benefit?
If this is just the US, isn’t the vaunted GND supposed to cost $94T over 10 years or $9.4T per year?
Sounds just like dilauded government…spend $9.4T to avoid spending $75B
They want to spend more than 125 times what they propose to avoid spending

April 26, 2023 10:50 pm

The BBC had this gem of “wisdom” to report yesterday:

“In March, sea surface temperatures off the east coast of North America were as much as 13.8C higher than the 1981-2011 average.”

Maybe someone emptied the jacuzzi off of Cape Cod Massachusetts when that reading was taken. But I’m pretty sure if the SST off of the east coast was almost 14⁰C above average, someone would have noticed. The Labrador Sea north of Newfoundland still has ice…

Last edited 1 month ago by johnesm
Jim Masterson
Reply to  johnesm
April 26, 2023 11:15 pm

The MSM rattles off anything just because it sounds bad. I noticed that Greta Thunberg quietly deleted her end of the world prediction for 2023. I guess we have a few more years these alarmists didn’t count on. One wonders if they really believe their nonsense.

Joseph Zorzin
Reply to  Jim Masterson
April 27, 2023 6:02 am

Doctor of Theology Thunberg!

Reply to  johnesm
April 27, 2023 12:12 am

The chances of the BBC knowing the difference between Fahrenheit and Centigrade is vanishingly small.

Ben Vorlich
Reply to  MCourtney
April 27, 2023 1:31 pm

The article also says

The average surface temperature of the world’s seas has increased by around 0.9C compared to preindustrial levels, with 0.6C coming in the last 40 years alone.

How do they know what the pre-industrial SST was? A complete map of Australia wasn’t published until about 1812. Regular ship traffic to Australia only began until late 18th so I can’t imagine any accurate value is available to give a value of around 0.9C or anything else

old cocky
Reply to  johnesm
April 27, 2023 12:32 am

“In March, sea surface temperatures off the east coast of North America were as much as 13.8C higher than the 1981-2011 average.”

Perhaps somebody left out the punctuation, and it should have been “… as much as 13.8C; higher than the 1981-2011 average.”

Peta of Newark
Reply to  old cocky
April 27, 2023 1:18 am

This is a zoomed in screenshot (09:15BST 27Apr23) – they certainly did miss the punctuation.

and 1,500+ commentators on the story missed it and after 2 days it’s still not been corrected
(I didn’t read them all, life’s too short)

This is how you know, “You Can Trust The BBC”
they keep telling us so it must be true

edit to PS: duh
It was computer generated text = somebody talked into (programmed/dictated to) A Machine.
need I say more…………..

BBC Sea Surface Temp.PNG
Last edited 1 month ago by Peta of Newark
Right-Handed Shark
Reply to  old cocky
April 27, 2023 2:43 am

Left out, or deliberately omitted?

Dave Andrews
Reply to  old cocky
April 27, 2023 7:37 am

The Grauniad 27th April runs a similar sensational story but the graphic it shows. from Noaa has the 1982-2011 mean showing the temp at this time in April at about 20.25 degrees C and 24th April 2023 at 21 degrees C

Joseph Zorzin
Reply to  johnesm
April 27, 2023 6:02 am

Anyone who tries swimming in the ocean north of Cape Cod knows how dam cold it is. Several degrees warmer (F) would be nice.

Henry Pool
Reply to  Joseph Zorzin
April 27, 2023 7:43 am

The oceans in the Nh are now warming 5x faster than in the Sh.
Wood for Trees: Interactive Graphs

I wonder what is going on. I suspect it is excessive algae and seaweed growth.
Anyone has a better idea?

Henry Pool
Reply to  Henry Pool
April 27, 2023 7:53 am

I notice that in the Netherlands, they have an increasing trend in sunshine hours from about 1995. Can you believe it. I predicted more sunshine at the higher lats.
There is your source for more algae and sea weed.

Joseph Zorzin
Reply to  Henry Pool
April 27, 2023 7:55 am

I suggest the 5x thing is false. I say that because if you scan news stories around the planet- you’ll find that every place is warming faster than every other place.

Henry Pool
Reply to  Joseph Zorzin
April 27, 2023 8:23 am

Did you not read that graph that I submitted??

Bryan A
Reply to  Henry Pool
April 27, 2023 4:06 pm

But isn’t the Southern Ocean warming twice as fast as anyplace else?

Reply to  johnesm
April 27, 2023 7:52 am

It was missing a comma immediately after the 13.8 C. The proofreader remains horribly embarrassed.

Coeur de Lion
April 26, 2023 11:50 pm

Argo buoys show infinitesimal increases down to 1900 metres since 2004 and really infinitesimal at depth. Who’s right

Hans Erren
April 27, 2023 1:38 am

The use of cumulative CO2 emissions is ludicrous, as CO2 does not stay in the atmosphere but is seeping out with a halving time of 34 years.

Last edited 1 month ago by Hans Erren
Steve Case
April 27, 2023 2:02 am

“First, as you surely know by now, RCP8.5…” 

Representative Concentration Pathway Wikipedia

Peta of Newark
April 27, 2023 2:31 am

So many graphs – now it’s clear where they came from and where they’re going.

We’ve now got a world so paranoid and fearful of ‘other people’ – they are now hurting their own

edit to add “in other news”

Wonky Cycle Lane.PNG
Last edited 1 month ago by Peta of Newark
April 27, 2023 5:18 am

Is RCP 4.5 a “declare victory and go home” strategy a la the US peace talks with the Commie Vietnamese in 1973?
Or yet another moving of goalposts?
No matter how you cook it – this is a failure for the Climate Doom movement.

April 27, 2023 6:51 am

I really appreciate how you have described this. When I first read some of the critiques of the “RCP8.5 is business as usual” memes I couldn’t help but wonder why they were not also talking about the need to re-think benchmarks.

This is a very important article and I plan to share it widely. Thanks for taking the time to spell it out so clearly.

April 27, 2023 3:29 pm

It’s pretty simple to refute the validity of RCP4.5. Just compare the projections of warming and sea level rise to observed trends. I’ve added RCP2.6 projections underneath to illustrate the fact that observed trends of the natural world match most closely with RCP2.6, the “all hands on deck in every country to ‘combat’ climate change” scenario.

Temperate change by 2100

RCP4.5: +1.8 °C, range of 1.1 to 2.6
UAH trend: +1.3 °C
RCP2.6: +1.0 °C, range of 0.3 to 1.7

Sea level rise by 2100

RCP4.5: +0.47 meters, range of 0.32 to 0.63
Satellite: +0.34 meters, range of 0.30 to 0.38
RCP2.6: +0.40 meters, range of 0.26 to 0.55

Global climate seems content to do its own thing with humans having very little impact; no crisis anywhere in sight.

Last edited 1 month ago by stinkerp
old cocky
Reply to  stinkerp
April 27, 2023 5:29 pm

There’s too much overlap to be able to distinguish between the hypotheses unless the observations are near the tails.

April 28, 2023 4:52 am

“So if you are a researcher and you think, “Hey, maybe I’ll do a comparison of XYZ in RCP8.5 and compare it to RCP4.5 to illustrate the benefits of mitigation”

Just say no”

Good advice, but the problem is that some organisation will have offered the grant money to enable said researcher to write such a paper, and said researcher will get another paper out of it to add to his/her publications list. Saying ‘yes’ seems so much more attractive.

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