In your summary you use straw men when a better approach is suggested.
You say,
"The amendment rests on two false premises: 1) that NCA5 presents RCP8.5 and SSP5-8.5 results as expected, baseline, or business-as-usual futures..."
I would change it to,
"The amendment rests on the false premise that NCA5 presents RCP8.5 and SSP-8.5 as ** anything other than ** an illustrative, potentially worst case, scenario for comparison with the other scenarios..."
As I noted in Notes - the fiercest critics of 8.5 appear to be those promoting the kinds of unlimited emissions absence-of-policies that make it most plausible.
These seem to be the people seeking to save fossil fuels from global warming as their priority, who use economic alarmist and regulatory alarmist fears - real doomists, so fearful of facing up to reality they take comfort in denying it. The ones who are opposed to Net Zero and even more opposed to Real Zero and routinely oppose and obstruct and denigrate the growth of the Renewable Energy that is a crucial element in expectations of BAU having lower emissions than previously thought.
I have no real trust in Net Zero or the CCS and Carbon Offsets and CDR that seems crucial to it; even aside from their intrinsic problems (leakages and drought and fires, ie climate change driven reversals) those together would have to become the largest industry in the world, entirely funded by taxation and levies on industry.
My other concern is the scenarios where emissions reductions stall and emissions continue at significant levels for enough time that very high CO2 levels are reached.
Agreed that it is worth pushing back on the misinformation around RCP8.5. But I think it may be time for the community to move the conversation to the CMIP7 Medium and High scenarios.
The message there is a good one: the scenario designers listened. There are no more no-policy baselines. The range now starts from current policy and asks what happens if it strengthens, holds, or is rolled back. That is precisely what the critics said they wanted.
And it doesn't help them. Medium is current policies frozen at 2025 levels, and it reaches 2.9 °C in 2100 and keeps climbing to 4 °C in 2200 and stays there for centuries. High is what a rollback looks like and gets to approximately 6.5 °C. Those are the plausible futures now, arrived at on the critics' own terms — and to me they are not acceptable outcomes.
If other climate scientists and the IPCC listened to Dr James Hsnsen we wouldn't be in this mess and all the people NOW posting things are worse would have saved face.
Thank Hansen. Treat him with alot more R-E-S-P-E-C-T.
This is tone trolling to avoid the fact that Hansen overestimates ECS.
"Paleoclimate pattern effects help constrain climate sensitivity and 21st-century warming
[...]
Accounting for paleoclimate pattern effects produces a best estimate (median) for modern climate sensitivity of 2.8 °C and 66% CI of 2.4 to 3.4 °C (90% CI: 2.1 to 4.0 °C), substantially reducing uncertainty in projections of 21st-century warming."
None of what you said addresses the evidence that Hansen's equilibrium climate sensitivity (ECS) estimate of 4.8°C is too high. His 2023 paper supported his estimate by citing evidence from the Pliocene and the Last Glacial Maximum ("Global warming in the pipeline"). But the 2026 paper I cited above showed the Pliocene and Last Glacial Maximum support an ECS of ~3°C. That's consistent with ECS estimates from the IPCC's 2021 Sixth Assessment Report, Sherwood 2020, etc.
"An assessment of Earth's climate sensitivity using multiple lines of evidence"
"Opinion: Can uncertainty in climate sensitivity be narrowed further?"
Science is not behold to your ideological goals. Fact don't care about people's feelings.
I trust a good surgeon's expertise. I don't tell him before my heart operation that his procedure is wrong and to operate the way I say because I know better.
Btw, this is a moot argument. Let's move with the common denominator we share is that we are heating up fast and the ECS is just an arbitrary number and the ECS's we both subscribe are super catastrophic since mitigation and adaptation are pititation :)
Jeff... Jim Hansen recommended that we return to the "safe" atmosphere containing 350 ppm. The amount present when he testified before Congress in 1988 when the global temperature was well above his 1950-1980 base period value of 59°F... 15°C. That would require the capture and geological storage of more than 500 billion metric tons of CO2. Today's temperature is not much different than it was back then in spite of its much higher CO2 value.
Provide evidence, please. 1.5C When global temperatures hit 1.6°C above pre-industrial levels, it represents a climate state that human civilization has never experienced before in recorded history. For the entirety of modern human history, global temperatures have been remarkably stable. The difference between the coldest and warmest centuries between 1 AD and 1900 AD was at most 0.5°C. A jump to 1.6°C is completely outside the bounds of the climate stability that allowed human agriculture and cities to flourish.
You're disinforming, as usual, by ignoring the difference between absolute temperature vs. temperature anomalies. You've been told multiple times why temperature anomalies are preferable to absolute temperature. And it's already been shown that Hansen's 1988 work accurately projected subsequent warming, especially in terms of iTCR. His current ECS, though, is higher than that 1988 work and is too high.
Actually, Jim acknowledges 350 ppm level is a warming level( of course less than our current 430 ppm ). 280 ppm is almost a sure safe spot. We got T ton(s) not G tons to drawdown.
We are warming as the fire is on steroids now. We are appreciable hotter than the 1950-1980 period given the time span.
Jeff... in 1995 Hansen told us that the global average temperature was above his 1950-1980 base period value of 59°F.
New York Times, January 1996: The average temperature was 58.7 degrees Fahrenheit, according to the British data, .07 of a degree higher than the previous record, established in 1990. The British figures, based on land and sea measurements around the world, are one of two sets of long-term data by which surface temperature trends are being tracked. The other, maintained by the NASA Goddard Institute for Space Studies in New York, shows the average 1995 temperature at 59.7 degrees, slightly ahead of 1990 as the warmest year since 1866. But the difference is within the margin of sampling error, and the two years essentially finished neck and neck.
One of the scientists, Dr. James E. Hansen of the National Aeronautics and Space Administration's Institute for Space Studies in Manhattan, said he used the 30-year period 1950-1980, when the average global temperature was 59 degrees Fahrenheit, as a base to determine temperature variations. He said his readings showed that the average global temperature rose about as much since the base period as it did from the 1880's to the base period - about half a degree in both cases. He stressed that these were estimates and that it would take millions of measurements to reach an accurate global average.
Compare that with what the temperature was last year.
We are now in 2026 and the temp and CO2 has increased substantially since Noone needed Dr Hansen
Yearly temp differences swagger but the slope of temp increase is getting exponentially. And Dr Hansen even has ECS pegged at 4.8C now. I would trust him.
An eloquent and informative argument not to contemplate any dilution to the ‘worst case scenario’ - the Earth’s Energy Imbalance is already alarming, warming already exceeds most model predictions and tipping points and feedback loops are closer than ever - and now we have a huge El Niño brewing. Cumulative emissions are still rising, wildfires are burning, glaciers are melting and CCUS just isn’t happening. Please can we take the climate (and biodiversity and pollution) crisis much, much more seriously. Every indicator I look at, shows the impacts getter worse than feared, not better than hoped.
Don't your referenced documents use the phrase "business as usual" to imply that this scenario is a realistic emissions scenario? I think you are dealing with a backlash against efforts to mislead the public -- to scare people -- about where we are heading, so you might be better off to suggest that realistic scenarios be used to evaluate possible policy decisions. Climate change is bad enough that we need to be doing things to gain control of the greenhouse gas content of the atmosphere, but IMO policy decisions are best when the inputs are realistic and accurate.
Dessler disagrees with your distortions of RCP8.5, as does Gavin Schmidt. The point remains that RCP8.5's forcing and warming can be reached without RCP8.5's emissions. That is a point you consistently evade.
That doesn't address the point that Dessler and Schmidt disagree with you. The fact remains that: 1) observed forcing for the post-2005 projection period exceeds RCP8.5, and 2) RCP8.5 more accurately projected global warming than did your inaccurate claims.
It seems like a problem then, that the CMIP7 emissions pathways do not include any pathways that assume a climate sensitivity at the high end of the confidence band. Am I misinterpreting something?
> are the temperatures predicted by today’s climate models driven by RCP8.5 implausible?
I don't know whether they are (IPCC thinks not) but I don't think your study addresses this question. You're studying properties of your model ensemble not the real climate system.
Seismologist here. I don’t like use of ‘worst case.’ It’s the worst of the various models considered, but there’s no guarantee that the real outcome after a number of years won’t be even worse.
There is no conspiracy here. Each views data( along with different data ) from different angles. They share with total GOOD INTENT what they conclude. These gentlemen know their stuff.
"in trying to understand future climate changes, our focus is not primarily on emissions. Rather, it is on temperature, which is what drives most climate impacts."
I thought that CO2 emissions is what drove temperature increases to impact climate. Can you explain?
In your summary you use straw men when a better approach is suggested.
You say,
"The amendment rests on two false premises: 1) that NCA5 presents RCP8.5 and SSP5-8.5 results as expected, baseline, or business-as-usual futures..."
I would change it to,
"The amendment rests on the false premise that NCA5 presents RCP8.5 and SSP-8.5 as ** anything other than ** an illustrative, potentially worst case, scenario for comparison with the other scenarios..."
Thank you for presenting these important arguments!
As I noted in Notes - the fiercest critics of 8.5 appear to be those promoting the kinds of unlimited emissions absence-of-policies that make it most plausible.
These seem to be the people seeking to save fossil fuels from global warming as their priority, who use economic alarmist and regulatory alarmist fears - real doomists, so fearful of facing up to reality they take comfort in denying it. The ones who are opposed to Net Zero and even more opposed to Real Zero and routinely oppose and obstruct and denigrate the growth of the Renewable Energy that is a crucial element in expectations of BAU having lower emissions than previously thought.
I have no real trust in Net Zero or the CCS and Carbon Offsets and CDR that seems crucial to it; even aside from their intrinsic problems (leakages and drought and fires, ie climate change driven reversals) those together would have to become the largest industry in the world, entirely funded by taxation and levies on industry.
My other concern is the scenarios where emissions reductions stall and emissions continue at significant levels for enough time that very high CO2 levels are reached.
Agreed that it is worth pushing back on the misinformation around RCP8.5. But I think it may be time for the community to move the conversation to the CMIP7 Medium and High scenarios.
The message there is a good one: the scenario designers listened. There are no more no-policy baselines. The range now starts from current policy and asks what happens if it strengthens, holds, or is rolled back. That is precisely what the critics said they wanted.
And it doesn't help them. Medium is current policies frozen at 2025 levels, and it reaches 2.9 °C in 2100 and keeps climbing to 4 °C in 2200 and stays there for centuries. High is what a rollback looks like and gets to approximately 6.5 °C. Those are the plausible futures now, arrived at on the critics' own terms — and to me they are not acceptable outcomes.
Can we ignore the trivia of "this or that proposal" - the words, statements, and targets.
Let’s focus. Our world is going to +3C in the next 25 years and to the “End-Permian” +5C by 2100.
Let’s make that the reality we need to address, ameliorate, and adapt to.
If other climate scientists and the IPCC listened to Dr James Hsnsen we wouldn't be in this mess and all the people NOW posting things are worse would have saved face.
Thank Hansen. Treat him with alot more R-E-S-P-E-C-T.
As Earth burns..
This is tone trolling to avoid the fact that Hansen overestimates ECS.
"Paleoclimate pattern effects help constrain climate sensitivity and 21st-century warming
[...]
Accounting for paleoclimate pattern effects produces a best estimate (median) for modern climate sensitivity of 2.8 °C and 66% CI of 2.4 to 3.4 °C (90% CI: 2.1 to 4.0 °C), substantially reducing uncertainty in projections of 21st-century warming."
"Who's you climate daddy, Atomsk?", you ask yourself RHETORICALLY in the 🪞 as Earth 🔥 and you claim Hansen wrong.
It's Medtime Atomsk.
None of what you said addresses the evidence that Hansen's equilibrium climate sensitivity (ECS) estimate of 4.8°C is too high. His 2023 paper supported his estimate by citing evidence from the Pliocene and the Last Glacial Maximum ("Global warming in the pipeline"). But the 2026 paper I cited above showed the Pliocene and Last Glacial Maximum support an ECS of ~3°C. That's consistent with ECS estimates from the IPCC's 2021 Sixth Assessment Report, Sherwood 2020, etc.
"An assessment of Earth's climate sensitivity using multiple lines of evidence"
"Opinion: Can uncertainty in climate sensitivity be narrowed further?"
Science is not behold to your ideological goals. Fact don't care about people's feelings.
I trust a good surgeon's expertise. I don't tell him before my heart operation that his procedure is wrong and to operate the way I say because I know better.
I do have alot of faith in Hansen. I trust him.
Btw, this is a moot argument. Let's move with the common denominator we share is that we are heating up fast and the ECS is just an arbitrary number and the ECS's we both subscribe are super catastrophic since mitigation and adaptation are pititation :)
Jeff... Jim Hansen recommended that we return to the "safe" atmosphere containing 350 ppm. The amount present when he testified before Congress in 1988 when the global temperature was well above his 1950-1980 base period value of 59°F... 15°C. That would require the capture and geological storage of more than 500 billion metric tons of CO2. Today's temperature is not much different than it was back then in spite of its much higher CO2 value.
We are 1.5C warmer
Warmer than what.... not how much.
Provide evidence, please. 1.5C When global temperatures hit 1.6°C above pre-industrial levels, it represents a climate state that human civilization has never experienced before in recorded history. For the entirety of modern human history, global temperatures have been remarkably stable. The difference between the coldest and warmest centuries between 1 AD and 1900 AD was at most 0.5°C. A jump to 1.6°C is completely outside the bounds of the climate stability that allowed human agriculture and cities to flourish.
You're disinforming, as usual, by ignoring the difference between absolute temperature vs. temperature anomalies. You've been told multiple times why temperature anomalies are preferable to absolute temperature. And it's already been shown that Hansen's 1988 work accurately projected subsequent warming, especially in terms of iTCR. His current ECS, though, is higher than that 1988 work and is too high.
https://github.com/hausfath/old-models-analysis
"Evaluating the performance of past climate model projections"
Actually, Jim acknowledges 350 ppm level is a warming level( of course less than our current 430 ppm ). 280 ppm is almost a sure safe spot. We got T ton(s) not G tons to drawdown.
We are warming as the fire is on steroids now. We are appreciable hotter than the 1950-1980 period given the time span.
Jeff... in 1995 Hansen told us that the global average temperature was above his 1950-1980 base period value of 59°F.
New York Times, January 1996: The average temperature was 58.7 degrees Fahrenheit, according to the British data, .07 of a degree higher than the previous record, established in 1990. The British figures, based on land and sea measurements around the world, are one of two sets of long-term data by which surface temperature trends are being tracked. The other, maintained by the NASA Goddard Institute for Space Studies in New York, shows the average 1995 temperature at 59.7 degrees, slightly ahead of 1990 as the warmest year since 1866. But the difference is within the margin of sampling error, and the two years essentially finished neck and neck.
One of the scientists, Dr. James E. Hansen of the National Aeronautics and Space Administration's Institute for Space Studies in Manhattan, said he used the 30-year period 1950-1980, when the average global temperature was 59 degrees Fahrenheit, as a base to determine temperature variations. He said his readings showed that the average global temperature rose about as much since the base period as it did from the 1880's to the base period - about half a degree in both cases. He stressed that these were estimates and that it would take millions of measurements to reach an accurate global average.
Compare that with what the temperature was last year.
Ken,
We are now in 2026 and the temp and CO2 has increased substantially since Noone needed Dr Hansen
Yearly temp differences swagger but the slope of temp increase is getting exponentially. And Dr Hansen even has ECS pegged at 4.8C now. I would trust him.
An eloquent and informative argument not to contemplate any dilution to the ‘worst case scenario’ - the Earth’s Energy Imbalance is already alarming, warming already exceeds most model predictions and tipping points and feedback loops are closer than ever - and now we have a huge El Niño brewing. Cumulative emissions are still rising, wildfires are burning, glaciers are melting and CCUS just isn’t happening. Please can we take the climate (and biodiversity and pollution) crisis much, much more seriously. Every indicator I look at, shows the impacts getter worse than feared, not better than hoped.
Don't your referenced documents use the phrase "business as usual" to imply that this scenario is a realistic emissions scenario? I think you are dealing with a backlash against efforts to mislead the public -- to scare people -- about where we are heading, so you might be better off to suggest that realistic scenarios be used to evaluate possible policy decisions. Climate change is bad enough that we need to be doing things to gain control of the greenhouse gas content of the atmosphere, but IMO policy decisions are best when the inputs are realistic and accurate.
I agree with you, NCA5 should be left alone:
https://rogerpielkejr.substack.com/p/i-wouldnt-start-from-here
Dessler disagrees with your distortions of RCP8.5, as does Gavin Schmidt. The point remains that RCP8.5's forcing and warming can be reached without RCP8.5's emissions. That is a point you consistently evade.
https://www.realclimate.org/index.php/archives/2026/05/scenarios-schmenarios/#comment-848299
You are in luck
Scenario dashboard coming this week!
That doesn't address the point that Dessler and Schmidt disagree with you. The fact remains that: 1) observed forcing for the post-2005 projection period exceeds RCP8.5, and 2) RCP8.5 more accurately projected global warming than did your inaccurate claims.
https://pubpeer.com/publications/0169783732C3DCCCC3CBDC6CAC0C8E#2
RCP8.5 and the other scenarios were retired by CMIP7. Yes, Dessler and Schmidt have both defended RCP8.5.
CMIP7 clearly did not find their (line of) arguments compelling.
Although CMIP7 does not cite our work, it is fully consistent with their decision to retire the flawed scenarios. Bravo 😎
It seems like a problem then, that the CMIP7 emissions pathways do not include any pathways that assume a climate sensitivity at the high end of the confidence band. Am I misinterpreting something?
> are the temperatures predicted by today’s climate models driven by RCP8.5 implausible?
I don't know whether they are (IPCC thinks not) but I don't think your study addresses this question. You're studying properties of your model ensemble not the real climate system.
Seismologist here. I don’t like use of ‘worst case.’ It’s the worst of the various models considered, but there’s no guarantee that the real outcome after a number of years won’t be even worse.
Ken,
You gotta trust Andrew and Zeke. As well as Jim.
There is no conspiracy here. Each views data( along with different data ) from different angles. They share with total GOOD INTENT what they conclude. These gentlemen know their stuff.
They are the right stuff.
"in trying to understand future climate changes, our focus is not primarily on emissions. Rather, it is on temperature, which is what drives most climate impacts."
I thought that CO2 emissions is what drove temperature increases to impact climate. Can you explain?
Thanks for using your valuable time to do the tiring work of combating lies
Hello Andrew,
Thanks a lot but what about the new CMIP7 which seems to withdraw the SSP8.5?
https://www.carbonbrief.org/explainer-the-cmip7-emissions-scenarios-and-how-they-explore-future-climate-change