Originally tweeted by Roger Pielke Jr. (@RogerPielkeJr) on Aug 9, 2021.
IPCC AR6 WG1
Some first comments
Think of these as work notes
Let’s go . . .
Let’s start with scenarios
That’s pretty big
“There is generally no likelihood associated with the scenarios assessed in this report”
So this means that the users of the scenarios have to assess the probabilities independently
This means: “The probability of scenarios with high emissions such as RCP8.5 or SSP5-8.5 is viewed as low”
They also said that a suitable scenario for the “lack of additional climate policy” (aka BAU) are “RCP4.5, RCP6.0 and SSP2-4.5 scenarios”:
You said it, kudos to the IPCC WG1🔥🔥
I’m not going to go too far in the weeds, but the IPCC WG1 has reverted to the SRES storyline approach
This means that interpreting the scenarios and the resulting projections is more difficult than saying that the IPCC is projecting the X or Y future
It’s a healthy development!
Underline this absolutely essential point
“The socio-economic assumptions and the feasibility or probability of individual scenarios are not part of the assessment”
Fortunately, you are in good hands here, as we have dealt intensively with the feasibility, more on that later
“IPCC is neutral with regard to the assumptions underlying the SSPs”
The IPCC thus recognizes that 8.5 scenarios have a “low probability” but still choose to remain “neutral” with regard to the scenario assumptions
As we shall see, this is not entirely true in practice
So which scenarios is the IPCC focusing on on AR6?
If it is “neutral”, we could assume that the focus of attention is pretty much the same in all scenarios (similar to when using SRES), since WG1 AR6 does not rate any one as more likely than another
On the other hand, the literature is strongly influenced by extreme scenarios …
So this is a BIG problem
The scenarios that the IPCC admits as unlikely dominate the report with 41.5% of all scenario mentions
The most likely scenarios under the current trends receive only 18.4% of the answers
Implausible scenarios (8.5 + 7.0) result in 53% of the answers, more than half!
From AR5 WG1 to AR6 WG1, the emphasis on 8.5 scenarios has increased dramatically
The table below shows that RCP8.5 mentions in AR5 WG1 accounted for 31.4% of the total scenario mentions, increasing to 41.5% in AR6
Focus on more realistic scenarios (4.5 & 6.0) decreased from 44.5% to 18.4%
AR5 table in the previous tweet from this paper:
Indeed, the IPCC AR6 WG1 is not neutral on scenario assumptions as it puts an overwhelming emphasis on improbable (your word), implausible (our word) scenarios
Since the IPCC also claims that there are no probabilities associated with scenarios, the emphasis on 8.5 needs to be interpreted
We have already explained the over-reliance on implausible 8.5 scenarios for dynamics in science
Other factors also play a role
See these two papers:
1-readable overview (read for free): https://issues.org/climate-change-scenarios-lost-touch-reality-pielke-ritchie/
2-Lots of details (DM for a copy):
But with its excessive reliance on 8.5 scenarios, the IPCC WG1 has prepared itself for appropriate criticism from friends and enemies
The unexpected turnaround in the use of scenarios from AR5 has also created the stage for confusion among experts, the media, and policy makers
That’s great too, and it’s good news
The IPCC has reduced its top-end estimate of climate sensitivity for the first time
The IPCC estimates that climate change is more severe than it has been since 1990
The best estimate remains the same, and the security at the lower end has also increased
Please have the comments and inquiries ready for our paper
OK, now to extremes. . .
Ch.8 on floods:
“The assessment of the observed trends in the order of magnitude of runoff, runoff and flooding remains a challenge due to the spatial heterogeneity of the signal and multiple drivers.”
Are floods increasing? Evidence doesn’t say that
Heat waves are increasing on a global scale (practically certain)
Frequency and intensity have increased on a global level (remarkable, only “probably”> 66% certainty)
I am very pleased that the IPCC has recognized that heavier rainfall does not mean increased flooding: “Higher rainfall does not always lead to larger floods”
We explained this in 1999 (Pielke and Downton 1999) 😎
There is little confidence in global trends
Some places above, some below
So don’t say floods are increasing
Don’t say they are “climate driven”
Obviously, without identified trends, there won’t be many opportunities for mapping
Do not say that floods are caused, driven or exacerbated by climate change. The evidence doesn’t support that.
AR5 discusses “drought”
AR6 discusses 4 types: meteorological, hydrological, agricultural, ecological
Different conclusions for everyone
Like AR5, low confidence in changes in M or H droughts, but medium confidence in changes in A&E
Identifying trends in tropical cyclones remains difficult, just as it does with AR5
There may be trends, but we can’t spot them (I always love this statement, if we can’t spot it, it can’t be that significant!)
This is fantastic
A clear sign that I’m Voldemort at the IPCC 😉
Also clear references to cherry picking tsk tsk
They point to normalized hurricane damage and cite a margin analysis with 24 citations while ignoring the final work with 1196 citations
The IPCC is really stretching out to say about TCs, relying on some studies that begin analyzing in 1980, when much more evidence is available
Do you know what the IPCC doesn’t mention?
Global TC landfalls (they mention landfalls in Madagascar and the US)
I wonder why not?
Our dataset was updated and published in the last WMO TC assessment
Curious what the IPCC forgot to add?
For NA & WP, about 70% of all landfalls, “the total number of hurricanes that hit land has decreased dramatically since the 1940s, while the number of large hurricane landfalls has shown no trend”.
Last point on the IPCC cherry-picking
Myself and my colleagues must surely be the most frequently cited authors on extremes and climate in order not to make it into the IPCC AR6 extreme chapter
Says a lot more about the IPCC than our peer-reviewed work
Back to the report. . .
Low confidence in trends of the past century in terms of frequency and intensity
Thunderstorms, tornadoes, hail, lightning
No uptrends detected
A new variable in AR6
Interestingly, the IPCC finds less extreme winds between 60N (~ Juneau) and 60S (~ Antarctica), so pretty much everywhere there are people
There goes the derecho attribution
“There is medium confidence that weather conditions that favor forest fires (fire weather) have become more likely over the past century in southern Europe, northern Europe, the United States, and Australia.”
Very consistent with AR5 (only a few more years of data, of course)
Little evidence of rising trends in floods, M&H drought, TCs, tornadoes, strong winds
But evidence of elevated temperatures, extreme rainfall, heat waves, fire weather, A&E drought
That’s all for now
I am now catching up on the many comments
Reply to paper inquiries
Thank you for reading!
I found this IPCC drought figure to be surprising No expected increase in drought in most of North America, Eastern Australia, Northern Europe, Asia – including India, Russia and China … in other words, where almost all of humanity lives This must be v good news, or?
Originally tweeted by Roger Pielke Jr. (@RogerPielkeJr) on Aug 9, 2021.