We conditioned the AR5 scenarios on consistency with recent trends and near term projections and arrived at a subset of plausible scenarios that project 2.2C (at the center) for 2100 https://iopscience.iop.org/article/10.1088/1748-9326/ac4ebf
So in your exercise, you might have used that subset of scenarios rather than the full AR6 range, which we know is full of implausible scenarios
So to answer the question, what effect has climate policy had?
We should not rely on scenarios as forecasts
Instead, we should rely on traditional methods of policy evaluation
So far, global decarbonization has not accelerated, as would be necessary for climate (mitigation) policy to have had a discernible effect to date
I would add for climate policy,to have "effective" effect, the creators of the policy firstly must consider seriously the horrors coming ( some here now ) and go on AR(High) to mitigate worst case events. We are in unchartered territory and ice cores can't reveal our new paradigm. And the banks don't give a hoot for broiled billions of poor people. More money for them.
I put faith in Dr James Hansen. He kicked off the global warming fiasco big-time in 88. He has been right on everything in the big pic. He even corrects himself. RCP0.0-1 it is. The -1 is the exponentially.
What will it take for us to care til we 🔥 ourselves?
You credit “…rapid declines in clean energy costs...” with bending the emissions curve downwards. Can this be correct?.
The cost of manufacturing wind turbine components and solar panels (W&S) has fallen, but several analyses show that the full unsubsidized cost of generating electricity with large-scale installations of these technologies is higher than using coal or natural gas. To quote one recent article, “…electrification relying on wind and solar technology is the most expensive and it gets more expensive the more wind and solar you utilize in the system” (see https://unpopular-truth.com/2026/04/25/rethinking-the-cost-of-electricity/).
This is not an argument for continued fossil fuel (FF) use, just a correction of a popular misconception. So-called modern renewable electricity sources, EVs, etc., may have reduced emissions by a few percentage points but this is not a reflection of lower input costs or consumer prices, but rather the displacement of FF generation. Continued reductions in emissions will likely result from lower availability and higher prices for petroleum and natural gas.
Meanwhile, the cost of generating so-called ‘renewable’ electricity will likely increase, partially because wind and solar technologies are highly FF-dependent at every stage of production from mining to installation and maintenance, but mainly because the costs associated with grid stabilization and synchronization rise in proportion to the share of electricity generation by wind and solar.
The statement below suggests the “climate science community” either doesn’t understand how modeling scenarios work or were using 8.5 for nefarious reasons or both. Can you seriously say this was just a miscommunication? I don’t understand how credentialed scientists would choose the worst case scenario to base their work on after reviewing the implausible assumptions it’s based upon. It seems to me that 8.5 fit the hockey stick and made better click bait.
“However, in part due to a breakdown in communication between the energy modeling community that develops the scenarios and the climate science community that uses them, RCP8.5 came to be incorrectly portrayed by many as the most likely “business as usual” scenario.”
8.5 here (as in RCP8.5) refers to the radiative forcing in 2100, not the warming. Its a very confusing naming convention, and thankfully for the AR7 we are changing it to just refer to scenarios as "Low", "Medium", "High", etc.
The F vs C note is well taken (I suspect its one of the reasons the US cares less about climate than the rest of the world!), but this Substack is not just intended for a US audience.
Naming conventions and promises can be confusing but the truth is the promises are lies. Seems like every nation ,when business strikes back ($), reverses ESG commitments. We burn because 💰 rules over people. The forgotten Newtonian Law.
Perhaps, but any American audience that cares about this subject will already be familiar with the Celsius values. C or F will make no difference to the rest.
I've lived a few years in Europe. I'm totally comfortable with the conversion. I'm even the one my Euro friends look to for the conversion when we're here or there. But like $5.99 is the same as $6, I still find it makes a difference even when you objectively know.
He said we can still see RCP8.5 implied temperatures even without RCP8.5 emissions.
RCP8.5 is an *emissions* scenario which is then translated to GHG concentrations, then to forcings, then to temperature. While we may not be on the worst case RCP8.5 emissions scenario, we are currently tracking the worst case RCP8.5 implied *forcing*.
Also note that there is a tremendous amount of assumed CDR in the translation from emissions to temperature. You can see it in the graphs that show negative emissions. But even those without below zero emissions assume a lot of CDR!
If Hansen is correct that ECS=4.5ºC, then even lower actual emissions can lead to RCP8.5 implied temperatures. We are currently on track for +2ºC warming in the 2030s and +3ºC in the 2050s/60s.
It's nice that we are not on track for RCP8.5 emissions. But we are on track for +3ºC or more warming and that is utterly catastrophic! We need to start taking climate action seriously.
I also have great faith in the godfather of climate science, James Hansen.
If I recall correctly, in his paper in 2025 he outlines how climate sensitivity is increasing as we clean up sulphur emissions in international shipping and reduce the smog in our cities.
He also notes (possibly in a past paper) that the UN estimates of future warming make no allowance for the feedback loops associated with irreversible tipping points, such as methane release from warming Arctic and sub Arctic regions and lost sea ice. These and others are already in play and as we reach plus 2C (which we will by mid-century), and others will kick in which will deliver plus 4C by 2100, almost regardless of what humanity does with its own emissions.
The consequences of passing +2C are therefore catastrophic.
Hansen also recommends using the paleo-climatic record to predict future outcomes and in this we see that these 2 factors, increasing climate sensitivity and irreversible tipping points and feedbacks will deliver +4C and more.
> Others have pointed out that RCP8.5 was never particularly plausible
Some would say that 8.5 was deliberately invented by climate alarmists to misled the general public into fast decarbonization.
While I applaud the authors for staying sane and scientifically objective, I'd like to remind everyone that business-as-usual projection of 3C of warming was always a baseline of sorts (not a real progress) b/c this was the estimate by both Charney and Hansen(scenario B). Much of the higher estimates were the product of what I said above.
I am sure there are some small percentage of climate concerned activists and even scientists who have spent time communicating about the potential absolute worst scenarios (e.g.. RCP8.5). However, the climate concerned people I am around (Citizens Climate Lobby, RepublicEN.org) and articles I seek out don't seem to focus on that. It is the more likely outcomes that get the attention and focus. The good news is that the trajectory for the most extreme higher temperatures has become less likely because there has been progress on the decreasing prices and accelerating deployment of clean energy solutions - while not enough yet.
At least from my perspective, the people/groups/think tanks that have spent the most time dwelling and communicating on things like RCP8.5 have been those trying to message against climate action. They seem to emphasize it to make people promoting the need for climate solutions (e.g. CCL) as radical - leftist - extremist, satanists, .... (ok - these examples I am listing seem to have gotten to extreme ... haha...).
So I am ok with putting RCP8.5 to rest, especially if it would provide less disinformation ammunition to those trying to delay climate action by using it as a talking point to frame those of us who are promoting reasonable climate solutions as extremists.....
P.S. - I am glad that our financial advisor includes a wide range of scenarios in their monte carlo analysis on how long our retirement funds might last. And I don't know of any right wing think tanks spending time arguing against those scenarios.
I wish you would post the truth of NDCs Zeke. Why countries refuse to commit to ongoing NDCs is because they know that honestly they break the Paris Accord.
As Earth 🔥 nations lie or put their heads in the sands. They don't wanna lie and they don't wanna look like the bad guys with the truth.
Thank you for the informative post. I have been reading your guest posts on Judith Curry's blog and elsewhere for years. Zeke, I wish you would use your prominence in climate science to help promote wider respect for science by equally calling out the mis-communicators on both sides and the media that hypes the those miscommunications.
Good stuff overall! But a few big issues
1. RCP8.5 was not designed as a "worst case" scenario.
It was the highest of the RCP set, and the only baseline.
But that by itself does not mean "worst case."
RCP8.5 comes from the MESSAGE family and originated in A2r (Riahi 2007) and A2 (SRES).
Of A2 SRES was explicit: "A2 is far from an environmental "worst case" scenario, even if it generally has the highest GHG emissions."
So maybe another communication failure.
2. You treat the AR6 baseline range as an accurate forecast distribution and then use that distribution to evaluate the effects of climate policy.
That range is contaminated by the return-to-coal hypothesis, flawed GDP assumptions, and erroneous population projections We dive into this here: https://iopscience.iop.org/article/10.1088/1748-9326/abcdd2
And updated here for AR6:
https://www.pnas.org/doi/full/10.1073/pnas.2214347119
We conditioned the AR5 scenarios on consistency with recent trends and near term projections and arrived at a subset of plausible scenarios that project 2.2C (at the center) for 2100 https://iopscience.iop.org/article/10.1088/1748-9326/ac4ebf
So in your exercise, you might have used that subset of scenarios rather than the full AR6 range, which we know is full of implausible scenarios
So to answer the question, what effect has climate policy had?
We should not rely on scenarios as forecasts
Instead, we should rely on traditional methods of policy evaluation
So far, global decarbonization has not accelerated, as would be necessary for climate (mitigation) policy to have had a discernible effect to date
Figure here: https://rogerpielkejr.substack.com/p/understanding-decarbonization
For climate policy to have an effect, we would have to see an inflection point in the curve at some point in the future
Climate policy may indeed be responsible for maintaining this rate of decline (and probably is)
I would add for climate policy,to have "effective" effect, the creators of the policy firstly must consider seriously the horrors coming ( some here now ) and go on AR(High) to mitigate worst case events. We are in unchartered territory and ice cores can't reveal our new paradigm. And the banks don't give a hoot for broiled billions of poor people. More money for them.
I put faith in Dr James Hansen. He kicked off the global warming fiasco big-time in 88. He has been right on everything in the big pic. He even corrects himself. RCP0.0-1 it is. The -1 is the exponentially.
What will it take for us to care til we 🔥 ourselves?
The words "faith" and "science" shouldn't be used in the same sentence.
Faith comes from good science. Are you a robot?
You credit “…rapid declines in clean energy costs...” with bending the emissions curve downwards. Can this be correct?.
The cost of manufacturing wind turbine components and solar panels (W&S) has fallen, but several analyses show that the full unsubsidized cost of generating electricity with large-scale installations of these technologies is higher than using coal or natural gas. To quote one recent article, “…electrification relying on wind and solar technology is the most expensive and it gets more expensive the more wind and solar you utilize in the system” (see https://unpopular-truth.com/2026/04/25/rethinking-the-cost-of-electricity/).
This is not an argument for continued fossil fuel (FF) use, just a correction of a popular misconception. So-called modern renewable electricity sources, EVs, etc., may have reduced emissions by a few percentage points but this is not a reflection of lower input costs or consumer prices, but rather the displacement of FF generation. Continued reductions in emissions will likely result from lower availability and higher prices for petroleum and natural gas.
Meanwhile, the cost of generating so-called ‘renewable’ electricity will likely increase, partially because wind and solar technologies are highly FF-dependent at every stage of production from mining to installation and maintenance, but mainly because the costs associated with grid stabilization and synchronization rise in proportion to the share of electricity generation by wind and solar.
The statement below suggests the “climate science community” either doesn’t understand how modeling scenarios work or were using 8.5 for nefarious reasons or both. Can you seriously say this was just a miscommunication? I don’t understand how credentialed scientists would choose the worst case scenario to base their work on after reviewing the implausible assumptions it’s based upon. It seems to me that 8.5 fit the hockey stick and made better click bait.
“However, in part due to a breakdown in communication between the energy modeling community that develops the scenarios and the climate science community that uses them, RCP8.5 came to be incorrectly portrayed by many as the most likely “business as usual” scenario.”
I think saying 15F (instead of 8.5) would be more understandable and effective when talking to an American audience. And 5.4F instead of 3C.
8.5 here (as in RCP8.5) refers to the radiative forcing in 2100, not the warming. Its a very confusing naming convention, and thankfully for the AR7 we are changing it to just refer to scenarios as "Low", "Medium", "High", etc.
The F vs C note is well taken (I suspect its one of the reasons the US cares less about climate than the rest of the world!), but this Substack is not just intended for a US audience.
Naming conventions and promises can be confusing but the truth is the promises are lies. Seems like every nation ,when business strikes back ($), reverses ESG commitments. We burn because 💰 rules over people. The forgotten Newtonian Law.
NDC= George Carlin joke
Perhaps, but any American audience that cares about this subject will already be familiar with the Celsius values. C or F will make no difference to the rest.
I've lived a few years in Europe. I'm totally comfortable with the conversion. I'm even the one my Euro friends look to for the conversion when we're here or there. But like $5.99 is the same as $6, I still find it makes a difference even when you objectively know.
We interviewed van Vuuren about this last week: https://youtube.com/live/MYWokv0Byas
He said we can still see RCP8.5 implied temperatures even without RCP8.5 emissions.
RCP8.5 is an *emissions* scenario which is then translated to GHG concentrations, then to forcings, then to temperature. While we may not be on the worst case RCP8.5 emissions scenario, we are currently tracking the worst case RCP8.5 implied *forcing*.
Also note that there is a tremendous amount of assumed CDR in the translation from emissions to temperature. You can see it in the graphs that show negative emissions. But even those without below zero emissions assume a lot of CDR!
If Hansen is correct that ECS=4.5ºC, then even lower actual emissions can lead to RCP8.5 implied temperatures. We are currently on track for +2ºC warming in the 2030s and +3ºC in the 2050s/60s.
It's nice that we are not on track for RCP8.5 emissions. But we are on track for +3ºC or more warming and that is utterly catastrophic! We need to start taking climate action seriously.
I also have great faith in the godfather of climate science, James Hansen.
If I recall correctly, in his paper in 2025 he outlines how climate sensitivity is increasing as we clean up sulphur emissions in international shipping and reduce the smog in our cities.
He also notes (possibly in a past paper) that the UN estimates of future warming make no allowance for the feedback loops associated with irreversible tipping points, such as methane release from warming Arctic and sub Arctic regions and lost sea ice. These and others are already in play and as we reach plus 2C (which we will by mid-century), and others will kick in which will deliver plus 4C by 2100, almost regardless of what humanity does with its own emissions.
The consequences of passing +2C are therefore catastrophic.
Hansen also recommends using the paleo-climatic record to predict future outcomes and in this we see that these 2 factors, increasing climate sensitivity and irreversible tipping points and feedbacks will deliver +4C and more.
Conclusion - do not reach +2C!!
> Others have pointed out that RCP8.5 was never particularly plausible
Some would say that 8.5 was deliberately invented by climate alarmists to misled the general public into fast decarbonization.
While I applaud the authors for staying sane and scientifically objective, I'd like to remind everyone that business-as-usual projection of 3C of warming was always a baseline of sorts (not a real progress) b/c this was the estimate by both Charney and Hansen(scenario B). Much of the higher estimates were the product of what I said above.
I am sure there are some small percentage of climate concerned activists and even scientists who have spent time communicating about the potential absolute worst scenarios (e.g.. RCP8.5). However, the climate concerned people I am around (Citizens Climate Lobby, RepublicEN.org) and articles I seek out don't seem to focus on that. It is the more likely outcomes that get the attention and focus. The good news is that the trajectory for the most extreme higher temperatures has become less likely because there has been progress on the decreasing prices and accelerating deployment of clean energy solutions - while not enough yet.
At least from my perspective, the people/groups/think tanks that have spent the most time dwelling and communicating on things like RCP8.5 have been those trying to message against climate action. They seem to emphasize it to make people promoting the need for climate solutions (e.g. CCL) as radical - leftist - extremist, satanists, .... (ok - these examples I am listing seem to have gotten to extreme ... haha...).
So I am ok with putting RCP8.5 to rest, especially if it would provide less disinformation ammunition to those trying to delay climate action by using it as a talking point to frame those of us who are promoting reasonable climate solutions as extremists.....
P.S. - I am glad that our financial advisor includes a wide range of scenarios in their monte carlo analysis on how long our retirement funds might last. And I don't know of any right wing think tanks spending time arguing against those scenarios.
I wish you would post the truth of NDCs Zeke. Why countries refuse to commit to ongoing NDCs is because they know that honestly they break the Paris Accord.
As Earth 🔥 nations lie or put their heads in the sands. They don't wanna lie and they don't wanna look like the bad guys with the truth.
AS EARTH 🔥
Thank you for the informative post. I have been reading your guest posts on Judith Curry's blog and elsewhere for years. Zeke, I wish you would use your prominence in climate science to help promote wider respect for science by equally calling out the mis-communicators on both sides and the media that hypes the those miscommunications.
Thanks for a great explainer!