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.
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
In your RCP8.5 is Officially Dead post, it looks like you may have used the emissions data from the preprint/discussion paper rather than the final values that are in the paper? The Zenodo link in the paper is to old, illustrative pathways that differ from those that made it to print. For example, the preprint version doesn’t include the HL pathway. Emissions in H are now lower, etc.
I used the Zenodo link from the version of the paper as it was posted in early April, I did note the missing HL (and one other). My understanding is that the final versions of the scenario data won’t be available until Sept. I’ll do a full update when that data is available.
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.
Worth zooming out from the RCP8.5 question for a moment. Even taking the new CMIP7 medium illustrative scenario at face value — the one designed to reflect current policy — Zeke's own plot lands on ~2.8°C by 2100 (van Vuuren et al. show closer to 3°C), and the post notes the same scenario reaches ~3.7°C by 2150. Extend that out: under continued positive emissions and the slow ocean response, central estimates rise above 4°C by 2200 and stay there for several centuries. And once we eventually get to net zero, Clark et al. (2016) and others show the system holds most of that warming for centuries — with full carbon cycle recovery on millennial timescales.
So the headline isn't "RCP8.5 retired, crisis downgraded." The temperature trajectory under the medium scenario is still catastrophic on any horizon longer than 2100 — which is where most of the impacts (sea level, ice sheets, ecosystem reorganization) actually play out.
Arguing over whether RCP8.5 should have been retired five years ago is a side discussion but some people just won't let it die. The central scenario itself is the alarm.
The emissions scenarios were never intended to be a forecast and have been greatly misused by some.
My issue is that emissions are not what counts, it is the sum of those as concentrations of CO2. How well known are emissions? Who is counting all the emissions by the military such as in the Iran war? Some estimates for the first 14 days in March suggested 5 million tonnes of CO2 emitted, but that was way back in March. 1 ppm in CO2 is 7.8 billion tonnes. So it could well be that by now.
Of course it is offset by all the ships stalled in the Gulf and cuts in use of petroleum products involuntarily. My hope is that this pushes many nations to really get on with dispensing with fossil fuels.
The biggest increases in actual CO2 concentrations were in 2023 and 2024 of well over 3 ppm. Even 2025 was over a 2 ppm increment. No sign yet of decreases in emissions from the actual concentrations recorded.
None of the new scenarios include wars and conflicts.
The Global Carbon Project has done pretty heroic work on giving us a reliable inventory (and closing the carbon budget as well as they can). There remain some uncertainties fossil CO2 emissions (as of 2024) were 37.8 ± 1.8 GtCO2.
Given what we know of emissions and sinks changes in atmospheric concentrations are not particularly surprising. There doesn't seem to be a particularly persistent imbalance: https://essd.copernicus.org/articles/18/3211/2026/
Finally! Some measured commentary on this! I swear i spend most of my time as science communicator and scientist trying to not give into the temptation to scaremonger because I know it drives clicks. Thank you for being a voice a reason...
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.
Our estimates of future warming include feedbacks such as methane release from the Arctic and sea ice loss, though uncertainties for these can be large. And paleoclimate evidence does not necessarily support a high ECS: https://www.pnas.org/doi/10.1073/pnas.2511370123
Hi Zack, you might be able to help with a query, most paleoclimate evidence is a result of intact biomes both on land and in the oceans, this shifts the Bowen ratio and directly influences the surface boundary heat where most life lives, when one looks at the reality of land based temperature departure from the average due to deviation from this evolutionary state this can be many times higher and has flow on effects throughout all human based systems. Can you direct me to any good literature which clearly shows the temperature projections of warming by the end of the century in this light? Many thanks for decades of diligent analysis.
It's interesting that you chose the word "godfather" instead of "father". I'm sure you didn't mean that he's a chief Mafioso ;) But no, he is not either. He stood on the shoulders of giants, and there were many. There is nothing unique about his contributions to science, only in his relentless activism.
The world was +2C warmer before and here we are. No, +2C won't be catastrophic, probably +3C as well.
There is no scientific evidence that irreversible tipping points actually exist, this is just a speculation in order to scare general public into fast and economically dangerous decarbonization. Methane, in particular, although very potent has a very short lifetime so it is not as dangerous as they tell you.
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?
Jeff, I'm sorry, but 'faith' does not come from good science, because "faith is the substance of things hoped for, the evidence of things not seen" (Hebrews 11:1 KJV). IOW, it's a trap for the unwary! Science, OTOH, explicitly seeks to neutralize hope's tendency to fool itself, by relying only on the evidence of things seen the same way by trained, disciplined peers.
I'm not saying Hansen hopes that past emissions have already locked in severe, long-term warming that net-zero alone cannot stop, only that he hopes to be vindicated against the consensus of peers represented by our hosts (https://www.theclimatebrink.com/p/warming-in-the-pipeline-decoding). Your admiration for Hansen as you know him, leads you to hope his projections will accelerate decarbonization of the global economy. I, for one, hope to accelerate decarbonization by collective intervention in the otherwise-'free' market, but I also hope it can be done under popular sovereignty. I don't want either of my hopes to fool me about the realistic time frame!
I agree that 'we gotta care', but I'm not a theist, and I *hope* only to live a medically-assisted 'natural' lifespan, at most 25 more years. I am intensely curious to see what happens in that interval, and would love to see net-zero carbon-emissions achieved by then: but knowing what I do of the political power of concentrated carbon capital, I have no *faith* that it will be 8^(! In any case, Hansen's claim means merely that specified GMST-driven tipping points will be reached a few years sooner than otherwise. I *hope* it's later. Enough said.
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.
To your last point: Monte-Carlo simulations require knowledge of probability distributions which are in this case unknown. So your advisor assigns those probs subjectively. You should be aware of this limitation.
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.
AI is likely to increase global emissions by around 0.3% by 2030 (assuming a 10% increase in US electricity use and pretty small impacts elsewhere), which is not nothing but probably not enough to counterbalance other downward pressure. After 2030 we really don't know what will happen and it becomes increasingly speculative, both in terms of AI energy demand and rates of power sector decarbonization.
May I ask where this estimate is coming from? From what I read,
"Data centers currently account for about 1% to 2% of global electricity consumption, and this figure is expected to rise significantly due to the increasing demands of artificial intelligence, potentially reaching up to 21% of overall global energy demand by 2030."
If we take the IEA base case thats ~1% of global emissions (so a bit higher than just US electricity use changes would imply), and 1.4% in their high end case.
2) More importantly, atmospheric concentrations of carbon dioxide are at record levels and still increasing.
2) Even if emissions have plateaued in some places, it is not because so-called green renewables are cheaper as stated in the original article, but because, as you say, countries are "retiring a lot of coal". This is having the effect of raising the consumer price of electricity.
NB: The Israeli-US vs Iran folly may be the catalyst that triggers sustained emissions reductions, but it won't be a pretty sight.
Two true statements: estimations of anthropogenic emissions have plateaued; observations of atmospheric concentrations of CO2 continue to rise, unabated. The rub is that the net effect of planetary changes set in motion through emissions to-date (CO2, CH4, N2O cycles) may come close to, fully replace or exceed the flatlining of direct human GHG emissions.
Thanks, you beat me to it. Zeke says that once anthropogenic CO2 emissions cease, natural drawdown will roughly balance long-term feedbacks to past anthropogenic forcing, to maintain GMST around the highest value before net-zero is reached, for at least a couple of centuries.
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.”
Its the former. Scenarios were a pretty quiet part of the climate world until 2019 or so, and most scientists using them had little sense that RCP8.5 was the 90th percentile of baseline scenarios back in 2011.
'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?'
Yes. Why does that surprise you? The "climate science community" is made up of people who've spent years studying diverse aspects of climate change, and iteratively debating their research with their trained, disciplined peers. But many of them are only expert within a narrow segment of the greater problem domain. And physical scientists, by and large, don't study economics.
To the public, "business as usual" has always meant "no collective intervention in fossil-fuel producer profits". Fortunately, there has been collective intervention around the world, through carbon pricing or public investment in alternative energy. The LCOE for renewables has fallen precipitously as a result. That has deflected the otherwise-'free' market away from previously worst-case scenarios! We can all be glad science has motivated humanity to collectively avert the existential threat of open-ended warming. Of course, more or less random economic downturns have also helped falsify worst-case emissions scenarios, but only disaster capitalists are happy about them.
So, you're learning that even rigorous training and relentless peer discipline can't abolish the limits of human capacity. Why do you even suggest 'nefarious reasons'? Hanlon's (or Heinlein's) Razor holds that we should not attribute to malice, what can adequately be explained by incompetence! The fatal flaw in pseudoskeptical climate conspiracism, is that it gives scientists too much credit. Do you imagine that a shadowy cabal of unnamed illuminati, with mysterious goals and superhuman foresight, formed a plan in the early 19th century to deceive the public 200 years hence, by recruiting generations of trained, genuine skeptics to beaver away by the thousands building multiple lines of false evidence, and nobody in on it has given the secret away?
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.
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.
This was what I came here to say. IPCC making another move that helps deniers - there is no reason to say 8.5 C is dead. Just the emissions scenarios seem unlikely at the same climate sensitivity assuming all stays the same all the way up. but it doesn't ocean changes atmosphere changes albedo changes and natural sources change. We hit 1.5 long before 2050 which was the obama era idea.
Another true statement, as long as emissions exceed removals, the residual will continue to increase. The point is, natural removals are not proportionately static and are declining. Under rising temperatures forest areas are transitioning from net CO2 sinks to sources; phytoplankton CO2 removals are declining; oceanic oxygen dead zones, source of N20 emissions, are increasing; permafrost carbon and CH4 stores are a ticking bomb. The long-term impact of these trends (which operate on different time scales to human actions) serve to shift the fulcrum. Our unwillingness to reduce human sources quick enough comes at the cost of having a declining ability to impact the balance later, no?
I'm glad to see that, through additional investigations, the climate science community is accepting the RCP 8.5 is not realistic. I would also like to see greater acceptance of the proven ability of the natural ocean and land sinks to continue to remove CO2 from the atmosphere at rates that are directly proportional to atmospheric concentrations. And of the proven role of engineering economics: Developing and deploying low- carbon, carbon-free and negative-carbon technologies -- that are economically-preferable to fossil-carbon technologies -- accelerates once they reach sufficient levels of acceptance in the marketplace. This is what is happening now with wind, solar and electrified vehicles (including BEVs, HEVs and PHEVs) and will also occur if we can get small, modular nuclear reactors, bio-fuels and fuel cells into the same space.
I fully agree, however Dr. Hausfather, inter alia, finds little warming "in the pipeline": i.e. he expects GMST to plateau soon after net-zero emissions is achieved, due to natural CO2 drawdown roughly balancing mid- and long-term feedbacks (https://www.carbonbrief.org/explainer-will-global-warming-stop-as-soon-as-net-zero-emissions-are-reached/). Zeke claims that's the consensus of his peers, and contrary to Hansen. IDK, but I'm inclined to trust the consensus over outliers, no matter how individually authoritative, until facts demonstrate otherwise.
Thank you for the excellent post! One problem is that there has been a reluctance in the scenario modeling community to designate scenarios as more or less likely, based on the assertion that 'we cannot run experiments on societies and count frequency of outcomes'. This is a theoretically flawed argument: likelihood can be judged without experimenting. Our recent paper shows that careful methods of probabilistically forecasting renewables would yield much less emissions than 'current policy' scenarios, to say nothing about RCP8.5. More attention should be paid to such projections vis-a-vis extreme cases.
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.
RCPwaf RCP we are f'd is even if we get some s*** together
Reflect baby reflect
Catch up on cc
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)
In your RCP8.5 is Officially Dead post, it looks like you may have used the emissions data from the preprint/discussion paper rather than the final values that are in the paper? The Zenodo link in the paper is to old, illustrative pathways that differ from those that made it to print. For example, the preprint version doesn’t include the HL pathway. Emissions in H are now lower, etc.
I used the Zenodo link from the version of the paper as it was posted in early April, I did note the missing HL (and one other). My understanding is that the final versions of the scenario data won’t be available until Sept. I’ll do a full update when that data is available.
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.
Worth zooming out from the RCP8.5 question for a moment. Even taking the new CMIP7 medium illustrative scenario at face value — the one designed to reflect current policy — Zeke's own plot lands on ~2.8°C by 2100 (van Vuuren et al. show closer to 3°C), and the post notes the same scenario reaches ~3.7°C by 2150. Extend that out: under continued positive emissions and the slow ocean response, central estimates rise above 4°C by 2200 and stay there for several centuries. And once we eventually get to net zero, Clark et al. (2016) and others show the system holds most of that warming for centuries — with full carbon cycle recovery on millennial timescales.
So the headline isn't "RCP8.5 retired, crisis downgraded." The temperature trajectory under the medium scenario is still catastrophic on any horizon longer than 2100 — which is where most of the impacts (sea level, ice sheets, ecosystem reorganization) actually play out.
Arguing over whether RCP8.5 should have been retired five years ago is a side discussion but some people just won't let it die. The central scenario itself is the alarm.
The emissions scenarios were never intended to be a forecast and have been greatly misused by some.
My issue is that emissions are not what counts, it is the sum of those as concentrations of CO2. How well known are emissions? Who is counting all the emissions by the military such as in the Iran war? Some estimates for the first 14 days in March suggested 5 million tonnes of CO2 emitted, but that was way back in March. 1 ppm in CO2 is 7.8 billion tonnes. So it could well be that by now.
Of course it is offset by all the ships stalled in the Gulf and cuts in use of petroleum products involuntarily. My hope is that this pushes many nations to really get on with dispensing with fossil fuels.
The biggest increases in actual CO2 concentrations were in 2023 and 2024 of well over 3 ppm. Even 2025 was over a 2 ppm increment. No sign yet of decreases in emissions from the actual concentrations recorded.
None of the new scenarios include wars and conflicts.
The Global Carbon Project has done pretty heroic work on giving us a reliable inventory (and closing the carbon budget as well as they can). There remain some uncertainties fossil CO2 emissions (as of 2024) were 37.8 ± 1.8 GtCO2.
Given what we know of emissions and sinks changes in atmospheric concentrations are not particularly surprising. There doesn't seem to be a particularly persistent imbalance: https://essd.copernicus.org/articles/18/3211/2026/
Finally! Some measured commentary on this! I swear i spend most of my time as science communicator and scientist trying to not give into the temptation to scaremonger because I know it drives clicks. Thank you for being a voice a reason...
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!!
Our estimates of future warming include feedbacks such as methane release from the Arctic and sea ice loss, though uncertainties for these can be large. And paleoclimate evidence does not necessarily support a high ECS: https://www.pnas.org/doi/10.1073/pnas.2511370123
Hi Zack, you might be able to help with a query, most paleoclimate evidence is a result of intact biomes both on land and in the oceans, this shifts the Bowen ratio and directly influences the surface boundary heat where most life lives, when one looks at the reality of land based temperature departure from the average due to deviation from this evolutionary state this can be many times higher and has flow on effects throughout all human based systems. Can you direct me to any good literature which clearly shows the temperature projections of warming by the end of the century in this light? Many thanks for decades of diligent analysis.
It's interesting that you chose the word "godfather" instead of "father". I'm sure you didn't mean that he's a chief Mafioso ;) But no, he is not either. He stood on the shoulders of giants, and there were many. There is nothing unique about his contributions to science, only in his relentless activism.
The world was +2C warmer before and here we are. No, +2C won't be catastrophic, probably +3C as well.
There is no scientific evidence that irreversible tipping points actually exist, this is just a speculation in order to scare general public into fast and economically dangerous decarbonization. Methane, in particular, although very potent has a very short lifetime so it is not as dangerous as they tell you.
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?
Jeff, I'm sorry, but 'faith' does not come from good science, because "faith is the substance of things hoped for, the evidence of things not seen" (Hebrews 11:1 KJV). IOW, it's a trap for the unwary! Science, OTOH, explicitly seeks to neutralize hope's tendency to fool itself, by relying only on the evidence of things seen the same way by trained, disciplined peers.
I'm not saying Hansen hopes that past emissions have already locked in severe, long-term warming that net-zero alone cannot stop, only that he hopes to be vindicated against the consensus of peers represented by our hosts (https://www.theclimatebrink.com/p/warming-in-the-pipeline-decoding). Your admiration for Hansen as you know him, leads you to hope his projections will accelerate decarbonization of the global economy. I, for one, hope to accelerate decarbonization by collective intervention in the otherwise-'free' market, but I also hope it can be done under popular sovereignty. I don't want either of my hopes to fool me about the realistic time frame!
You are right in quoting Paul.
I have faith in good intentions that Hansen has. All good comes from God.
We gotta care. Am a Christian. Seems like a thing we fear to admit.
I agree that 'we gotta care', but I'm not a theist, and I *hope* only to live a medically-assisted 'natural' lifespan, at most 25 more years. I am intensely curious to see what happens in that interval, and would love to see net-zero carbon-emissions achieved by then: but knowing what I do of the political power of concentrated carbon capital, I have no *faith* that it will be 8^(! In any case, Hansen's claim means merely that specified GMST-driven tipping points will be reached a few years sooner than otherwise. I *hope* it's later. Enough said.
Well, theist or agnostic we agree we gotta care. Point gets attacked when I trust James Hansen.
ESS and ECS I trust him on. Because he's right.
I'll give you 3 guesses.
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.
To your last point: Monte-Carlo simulations require knowledge of probability distributions which are in this case unknown. So your advisor assigns those probs subjectively. You should be aware of this limitation.
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.
Global CO2 emissions have plateaued, largely because we are building more clean energy and retiring a lot of coal. In the US there is also a big story around gas displacing coal, but thats less the case in Europe and elsewhere. https://www.carbonbrief.org/analysis-fossil-fuel-co2-emissions-to-set-new-record-in-2025-as-land-sink-recovers/
But now we are witnessing an exponential growth in power demand due to AI. Is it not likely that emissions will start increasing again?
AI is likely to increase global emissions by around 0.3% by 2030 (assuming a 10% increase in US electricity use and pretty small impacts elsewhere), which is not nothing but probably not enough to counterbalance other downward pressure. After 2030 we really don't know what will happen and it becomes increasingly speculative, both in terms of AI energy demand and rates of power sector decarbonization.
May I ask where this estimate is coming from? From what I read,
"Data centers currently account for about 1% to 2% of global electricity consumption, and this figure is expected to rise significantly due to the increasing demands of artificial intelligence, potentially reaching up to 21% of overall global energy demand by 2030."
https://mitsloan.mit.edu/ideas-made-to-matter/ai-has-high-data-center-energy-costs-there-are-solutions
This Carbon Brief piece has a good compilation of published energy use estimates: https://www.carbonbrief.org/ai-five-charts-that-put-data-centre-energy-use-and-emissions-into-context/
If we take the IEA base case thats ~1% of global emissions (so a bit higher than just US electricity use changes would imply), and 1.4% in their high end case.
Three quick points:
1) It's actually not clear that global carbon dioxide emissions have plateaued:
"Global carbon dioxide emissions from fossil fuels and industry totaled 38.11 billion metric tons (GtCO₂) in 2025. Emissions are projected to have risen 0.87 percent in 2025 to reach a record high of 38.11 GtCO₂. Since 1990, global CO₂ emissions have increased by more than 69 percent." True, US emissions have declined slightly but much of this is due to deindustrialization (See: https://www.statista.com/statistics/276629/global-co2-emissions/?srsltid=AfmBOoqMF0VDzD-1dv-E1hlZuaYnFXt5pdZhq8OjnQI4Xc3lFoc_NA06)
2) More importantly, atmospheric concentrations of carbon dioxide are at record levels and still increasing.
2) Even if emissions have plateaued in some places, it is not because so-called green renewables are cheaper as stated in the original article, but because, as you say, countries are "retiring a lot of coal". This is having the effect of raising the consumer price of electricity.
NB: The Israeli-US vs Iran folly may be the catalyst that triggers sustained emissions reductions, but it won't be a pretty sight.
Its pretty unambiguous that global CO2 emissions have plateaued (e.g. flattened), even if they have not necessarily peaked. Here is the annual update of the GCP results that Pierre Friedlingstein and I wrote for Carbon Brief this year (with links to the underlying GCP data): https://www.carbonbrief.org/analysis-fossil-fuel-co2-emissions-to-set-new-record-in-2025-as-land-sink-recovers/
Two true statements: estimations of anthropogenic emissions have plateaued; observations of atmospheric concentrations of CO2 continue to rise, unabated. The rub is that the net effect of planetary changes set in motion through emissions to-date (CO2, CH4, N2O cycles) may come close to, fully replace or exceed the flatlining of direct human GHG emissions.
Constant emissions will cause rising atmospheric CO2. This is why emissions must drop significantly.
Thanks, you beat me to it. Zeke says that once anthropogenic CO2 emissions cease, natural drawdown will roughly balance long-term feedbacks to past anthropogenic forcing, to maintain GMST around the highest value before net-zero is reached, for at least a couple of centuries.
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.”
Its the former. Scenarios were a pretty quiet part of the climate world until 2019 or so, and most scientists using them had little sense that RCP8.5 was the 90th percentile of baseline scenarios back in 2011.
'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?'
Yes. Why does that surprise you? The "climate science community" is made up of people who've spent years studying diverse aspects of climate change, and iteratively debating their research with their trained, disciplined peers. But many of them are only expert within a narrow segment of the greater problem domain. And physical scientists, by and large, don't study economics.
To the public, "business as usual" has always meant "no collective intervention in fossil-fuel producer profits". Fortunately, there has been collective intervention around the world, through carbon pricing or public investment in alternative energy. The LCOE for renewables has fallen precipitously as a result. That has deflected the otherwise-'free' market away from previously worst-case scenarios! We can all be glad science has motivated humanity to collectively avert the existential threat of open-ended warming. Of course, more or less random economic downturns have also helped falsify worst-case emissions scenarios, but only disaster capitalists are happy about them.
So, you're learning that even rigorous training and relentless peer discipline can't abolish the limits of human capacity. Why do you even suggest 'nefarious reasons'? Hanlon's (or Heinlein's) Razor holds that we should not attribute to malice, what can adequately be explained by incompetence! The fatal flaw in pseudoskeptical climate conspiracism, is that it gives scientists too much credit. Do you imagine that a shadowy cabal of unnamed illuminati, with mysterious goals and superhuman foresight, formed a plan in the early 19th century to deceive the public 200 years hence, by recruiting generations of trained, genuine skeptics to beaver away by the thousands building multiple lines of false evidence, and nobody in on it has given the secret away?
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.
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.
This was what I came here to say. IPCC making another move that helps deniers - there is no reason to say 8.5 C is dead. Just the emissions scenarios seem unlikely at the same climate sensitivity assuming all stays the same all the way up. but it doesn't ocean changes atmosphere changes albedo changes and natural sources change. We hit 1.5 long before 2050 which was the obama era idea.
Another true statement, as long as emissions exceed removals, the residual will continue to increase. The point is, natural removals are not proportionately static and are declining. Under rising temperatures forest areas are transitioning from net CO2 sinks to sources; phytoplankton CO2 removals are declining; oceanic oxygen dead zones, source of N20 emissions, are increasing; permafrost carbon and CH4 stores are a ticking bomb. The long-term impact of these trends (which operate on different time scales to human actions) serve to shift the fulcrum. Our unwillingness to reduce human sources quick enough comes at the cost of having a declining ability to impact the balance later, no?
How contradictory! Why would you say that after telling me you don't even visit Curry's blog. Ignorance is bliss?
I'm glad to see that, through additional investigations, the climate science community is accepting the RCP 8.5 is not realistic. I would also like to see greater acceptance of the proven ability of the natural ocean and land sinks to continue to remove CO2 from the atmosphere at rates that are directly proportional to atmospheric concentrations. And of the proven role of engineering economics: Developing and deploying low- carbon, carbon-free and negative-carbon technologies -- that are economically-preferable to fossil-carbon technologies -- accelerates once they reach sufficient levels of acceptance in the marketplace. This is what is happening now with wind, solar and electrified vehicles (including BEVs, HEVs and PHEVs) and will also occur if we can get small, modular nuclear reactors, bio-fuels and fuel cells into the same space.
I fully agree, however Dr. Hausfather, inter alia, finds little warming "in the pipeline": i.e. he expects GMST to plateau soon after net-zero emissions is achieved, due to natural CO2 drawdown roughly balancing mid- and long-term feedbacks (https://www.carbonbrief.org/explainer-will-global-warming-stop-as-soon-as-net-zero-emissions-are-reached/). Zeke claims that's the consensus of his peers, and contrary to Hansen. IDK, but I'm inclined to trust the consensus over outliers, no matter how individually authoritative, until facts demonstrate otherwise.
Thank you for the excellent post! One problem is that there has been a reluctance in the scenario modeling community to designate scenarios as more or less likely, based on the assertion that 'we cannot run experiments on societies and count frequency of outcomes'. This is a theoretically flawed argument: likelihood can be judged without experimenting. Our recent paper shows that careful methods of probabilistically forecasting renewables would yield much less emissions than 'current policy' scenarios, to say nothing about RCP8.5. More attention should be paid to such projections vis-a-vis extreme cases.