Incredibly extreme and popular climate scenarios RCP8.5 last week on President Trump’s executive order “restores gold standard science.” [emphasis, links added]
Ironically, the Trump administration’s characteristics of RCP8.5 have not fully met the “gold standard” or even the “bronze standard”.
EO points out:
[Federal a]Gencies used Representative Concentration Pathway (RCP) Scheme 8.5 to assess the potential impact of climate change in “higher” warming scenarios. RCP 8.5 is a worst-case scenario based on extremely unlikely assumptions such as coal use at the end of the century, exceeding estimates of recoverable coal reserves. Scientists warn that using RCP 8.5 as a possible result is misleading.
RCP8.5 is not only “extremely impossible” – it is fake, which means its emission trajectory is already out of touch with reality.
We finally prove this in Burgess et al. In 2021, the following annotated figure appears from it:
The gap between the black arrow (RCP8.5) and the blue arrow (reality) shows that RCP8.5 is not only unlikely, but also impossible – this is already wrong.
The gap between RCP8.5 and reality has only become even bigger since we published this paper (keep your eye on it!).
An interesting thought experiment is to ask what the real world will need to “catch up” with RCP8.5. Starting from 2025, the real-world rationality of this “chasing” scenario begins in 2025, and the new scenario must be more aggressive than RCP8.5 and therefore more extreme.
If RCP8.5 is untrustworthy, then the new catching up to RCP8.5 scenario will inevitably be even more incredible.
Climate scientist Zeke Hausfath dismissed the Trump administration’s claim on RCP8.5, pointing out that the research community has moved on, and in the process he undoubtedly did it on THB (in no case directly involved!):):
It's weird, especially after a real transformation [RCP8.5] As you recognize that the possibility of high emission scenarios is constantly changing, please use post-AR6. It's almost like science is self-correcting.
Zeke's Get nothing It's wrong.
IPCC AR6 was released in 2021. From 2018 to 2021, Google Scholar reported 17,000 articles published using RCP 8.5. From 2022 to 2025, Google Scholar reported 16,900 articles published using RCP 8.5. Some transformations.
The Trump administration’s characteristics of RCP8.5 are not very correct, but its focus on continuing abuse is not wrong.
Since RCP 8.5 is outdated and incredible, it raises an important question: So what are the “worst case” climate scenarios used in policies?
While discussing this with colleagues, reading a few papers on rcp8.5 and chatting with AI models trained with such information, I concluded that the definition of “worst case” is very common, and it's simply a loop: The most extreme situation of IPCC-related scenario community development and provides for research purposes.
When marking the scenario as “worst case,” the climate community has never made a systematic scientific effort to assess rationality, or in the other extreme case, whether there may be more extreme cases that may be “deteriorated”.
Worst cases are important for policy and planning because they allow stress testing of proposed and formulated decisions to prevent lower possibilities, but policy makers may want reasonable outcomes to consider in strong decisions, which contribute to a highly uncertain future.
However, considering impossible or extremely unlikely situations can lead to wasted efforts, misplaced resources, and smart decisions.
So it is crucial to think carefully about the worst-case scenario and not only means the most extreme scenario I have.
In 2009, climate scientist Steve Schneider nature 2100 “worst case” with a concentration of 1,000 million (ppm) of carbon dioxide were described and temperatures rose close to 7 degrees Celsius.
Schneider's “worst case” is more extreme than the RCP8.5 that hasn't entered the scene yet, and seems to be based on the fact that 1,000 is a nice circular number, close to the most extreme case available at the time (A1FI).
But why stop 1,000 ppm and 7°C around 2100? Surely it would be worse than 1,500 ppm and 10°C? I can continue to invent more and more scenarios. However, from a reliable informed decision-making perspective, this exercise is obviously useless.
So there are “worse” questions about what? As Mike Hulme said:
“[T]Here are some futures above C (or even 2 degrees C) that are preferable to other futures that do not exceed these warming thresholds. We should not mistake one group for another. ”
Are the worst climate scenarios defined by temperature alone, or are health, wealth, fairness and human consequences? Who can decide?
Considering the rising temperature of RCP8.5, it is in a world considered very affluent. This is better or worse than a scenario with huge global poverty and inequality, but much lower temperature changes?
It turns out that defining a “worst case” is not a bloodless technical exercise, but a process of deep value, and it must be recognized that different people will see different results in different ways.
This makes the characteristics of the “worst outcome” inevitably political and a product of discussion, disagreement, debate and negotiation. There are many legitimate views on the composition of “worst case”.
The honest broker is written by climate expert Roger Pielke JR and backed by readers. If you value what you read here, consider subscribing to and supporting the work there.
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Top image: Molly Riley's official White House photo
