Last Updated 9.19.25 (G)

For decades, the world's leading authority on climate change, the Intergovernmental Panel on Climate Change (IPCC), has been plagued by problems of calculation and politicization. Here is its biggest one on climate sensitivity!

Job One for Humanity Editor's Forward

As it has done in earlier IPCC reports, the IPCC is still a grossly underestimating current and future climate change consequences and time tables. 

The IPCC's history of climate change calculation problems and other errors includes:

a. the politicization of climate science, 

b. serious errors in their calculations and assumptions, like the climate sensitivity controversy and 

c. other serious computer modeling omissions.

Items a, b, and c above all result in the gross underestimation of current climate change consequences, timetables, and remedies. The article below discusses the single most serious and important error in the IPCC's climate change calculations. It is called the IPCC climate sensitivity error.

Climate sensitivity is a critical measurement in climate science, serving as a mathematical constant in the various formulas used by the IPCC for many of its most critical climate calculations and predictions. Climate sensitivity measures how much the Earth's surface will cool or warm after a specified factor causes a change in its climate system, such as the amount of heating that would occur for a doubling of atmospheric carbon dioxide (CO2) concentration. 

Ensuring that the most correct climate sensitivity is used in climate computer models is crucial. If you get this mathematical constant and number wrong, all risk assessment and climate planning based on that incorrect climate sensitivity constant level will be flawed and potentially dangerous for anyone relying on it.

The IPCC's new climate sensitivity error makes the IPCC's current climate change consequences, consequence timetables, and remedies underestimated by at least 25% and probably much more! 

The following article offers an in-depth examination of the IPCC's error in estimating climate sensitivity. It is full of climate sensitivity science, but most people can still understand it.

When reading it, keep in mind that in order to determine the proper climate risk and threat assessment spectrum, one should always use the higher climate sensitivity range to envision the true risk and threat spectrum one faces.

In the article below, you get to be the judge of whether the IPCC has underestimated future climate change model projections by up to 25% or more by skewing the climate sensitivity calculations for the benefit of global fossil fuel interests. 

The following climate sensitivity section of this article was written by Peter Carter. Peter Carter was an expert reviewer for the United Nations' Intergovernmental Panel on Climate Change's (IPCC) fifth climate change assessment (AR5, 2014) and the IPCC’s 2018 Special Report on 1.5ºC. In 2018, he published Unprecedented Crime: Climate Science Denial and Game Changers for Survival, which he co-authored with Elizabeth Woodworth. He has published on climate change, biodiversity, and environmental health.

And more proof just arrived

1. James Hansen, the NASA scientist who warned the world about the dangers of global warming, has just published a new climate study that also supports disclosing the problems with the IPCC's current climate sensitivity numbers, which do not produce accurate predictions of climate consequences and timelines. Click here to see this very discouraging new 2023 climate study. It will be hard not to become very upset when you visit his new global heating temperature predictions, which are way beyond what we are told. Also, see his clear and scary comments on the false criticisms of his new study here.

2. As of 9.16.25, the climate sensitivity controversy has reached a new level with a recent study published claiming the real climate sensitivity is not 4.5 to 4.8 as in the new Hansen report, but actually 1.5. See our recent article on this here.

Special Climate Sensitivity Update to this original article

The single most critical climate change number is known as the climate sensitivity constant. Yet the IPCC, strongly influenced by the global fossil fuel cartel and fossil fuel-producing nations, has kept this all-important climate sensitivity constant artificially low despite continual protests by recognized climate scientists. 

According to a new 2023 peer-reviewed study, the correct climate sensitivity constant is 4.8 degrees Celsius, not the 3 degrees Celsius constant used by the IPCC over the last decades in almost ALL foundational climate change calculations.

The nearly 60% difference in the correct climate sensitivity constant compared to the IPCC's incorrect constant is not a minor or low-impact matter for your future.

The confirming 2023 study that disclosed this massive climate sensitivity error is called Global Warming in the Pipeline. It is by James Hansen et al. (James Hansen is the renowned climate scientist who, while at NASA in the 1980s, was primarily responsible for bringing the climate change emergency globally into the public mind.)

This newly corrected 4.8 degrees Celsius climate sensitivity constant powerfully indicates that climate consequences will be sooner and more severe than what our governments and the media are telling us.

It also means that the fossil fuel reduction amounts our governments have agreed to for reducing climate change (and which you frequently hear in the media) are also grossly underestimated by as much as 60%. 

This corrected 4.8 degrees Celsius climate sensitivity constant also suggests that we are already in the worst-case climate change scenario that honest climate researchers have been warning about, and for which humanity is not even remotely prepared. 

The worst outcome of having the climate sensitivity constant not being 3 degrees Celsius but 4.8 degrees Celsius (about 60% greater) is that almost all of the climate calculations provided by the IPCC upon which governments, media, and the whole world depend for accurate climate consequence severity estimates, consequence arrival timeframes, and the correct global fossil fuel reduction amounts are wildly not correct!

This new and corrected climate sensitivity constant of 4.8 degrees Celsius means that our worst fears have not only been confirmed, but also that they have been substantiated. It also means that when you include all additional factors listed below in reasons 1-5, almost all of the IPCC's climate change consequence severity and timeframe predictions, as well as their fossil fuel reduction amounts, are not just slightly incorrect.

The IPCC does not adequately assess global climate change for risk

The IPCC's 2021 Sixth Assessment climate sensitivity is fatally flawed, rendering the entire assessment flawed for policymaking purposes. 

Climate sensitivity is the fundamental metric used in climate change computer modeling. It determines by how much and how fast the global average (land-ocean) temperature will increase over the coming many centuries in response to an increased atmospheric concentration of carbon dioxide. 

Originally, in the 1980s, this climate sensitivity was chosen as a single fixed metric, representing a 3°C increase (from the pre-industrial period) if atmospheric carbon dioxide doubled, despite models consistently providing a wide range for climate sensitivity. Furthermore, the conclusion of a 2004 IPCC workshop on climate was that “sensitivity cannot be only one global number.”

Before I complain about the IPCC’s bad sense of science, I must say that the most important and truthful statements on climate change ever were made by the IPCC Chair at the last two UN climate conferences. 

At the opening of the UN Madrid COP25 (2 Dec 2019), IPCC Chair Hoesung Lee said: 

“Let me start by reminding you that our assessments show that climate stabilization implies that greenhouse gas emissions must start to peak from next year.” Global emissions had to be in decline by 2020!

At the opening of the UN Glasgow COP26  (31 October 2021), he said:

“It is now unequivocal that human influence is causing climate change, making extreme events more frequent and more severe. Global warming of 1.5°C and 2°C will be exceeded during this century unless immediate, rapid, and large-scale reductions in greenhouse gas emissions, especially of carbon dioxide and methane, occur in the near future.” Global emissions must be in decline now for any chance of limiting the catastrophic 2 °C rise. 

This was completely ignored by all concerned, who, to this day, claim that global warming can be limited to 1.5°C. This is an absurd, misleading falsehood. As the 2018 IPCC 1.5°C Report and the 2021 6th Assessment Working Group 1 report stated, the current emissions scenario puts the world on track to reach 1.5°C around 2030. This is now absolutely unavoidable.

However, both of these important climate science statements went completely unreported, despite the IPCC issuing them as media releases. 

Computer models designed by experts are used to estimate how the global climate, oceans, and land regions will change due to emissions of greenhouse gases (GHGs) that contribute to global warming. At every stage of the projections, from an increase in atmospheric CO2 to global surface warming and to the melting of Arctic sea ice (for example), the computer models project a very wide range of results. 

There are, therefore, fatal fundamental flaws in the IPCC 2021 sixth assessment (AR6) climate change science. Not only has the IPCC rejected risk, but it has also arrived at a climate sensitivity number lower than the latest models. 

There is nothing in climate science more important than the climate sensitivity because it is the metric used to calculate how much the average surface temperature warms for any given atmospheric concentration of CO2. 

As applied in climate change assessments, climate sensitivity has traditionally been represented by a single, virtually unchanging global average temperature increase, estimated from a doubling of atmospheric carbon dioxide. It is defined as the ultra-long-term equilibrium climate sensitivity (ES), which takes many hundreds of years. 

The metric is derived by computer modeling the increase in long-term equilibrium global surface temperature resulting from a doubling of atmospheric CO2. The computer models' results show a very wide range of temperature increases. The 2014 IPCC Fifth Assessment Report has a “likely” range of climate sensitivity of up to 4.5°C, but the IPCC assigned a fixed value of 3°C for policymaking purposes. The 2021 Sixth Assessment Report provided a likely upper range of 5°C, but the IPCC still offered only a single fixed value of 3°C for policymaking purposes. For risk, this is obviously the wrong choice. The right number for policymaking is the top of the “likely range” (IPCC). This was 4.5°C in 2014 and, with new models, 5°C in 2021. 

There is another reason why climate sensitivity must be at least 4.5°C, if not 5°C. Applying a single 3°C increase to project a temperature increase also yields a very wide range, which becomes even wider over time as the temperature increases further. Under the worst-case scenario (which the world is on, by the way), at 2050 the IPCC gives a temperature increase of 2.4°C, but the IPCC says the “likely range” is up to 3°C, and by 2100 the range increases to 5.7°C — while the IPCC gives 4.4°C for policymaking. In the best-case scenario for 2050, the IPCC gives 1.6°C, but the likely upper range is 2°C. 

The IPCC takes the median of this range, but the best model projection could be the one projecting the highest. A single fixed temperature increase has long been flawed for future projections, and the AR6 exacerbates this issue. It was originally used as a fixed standard to compare the different climate models developed by different climate centers. The IPCC’s climate sensitivity does not account for increased concentrations of the other main greenhouse gases, methane and nitrous oxide, which the scientists assume make no difference. 

The IPCC does not include in its climate sensitivity the extra warming from large planetary sources of amplifying feedbacks, nor the damage that warming does to forests, which reduces their capacity as a carbon sink, nor the reduced ocean carbon sink resulting from ocean heating. 

The new models (called CMIP6) projected much higher sensitivities, which were largely due to improved representations of cloud feedback as temperatures increase.  

In fact, there have always been some individual model results of sensitivity far higher than the 3°C used by the IPCC. 

Going back to the fifth assessment in 2014, some models, by studying actual cloud changes closely, had arrived at values much higher than 3°C, with upper limits higher still. Four out of ten models had an upper limit that was double the 3°C mean used. These upper ranges were so significantly higher than 3°C that applying a sensitivity higher than 3°C became imperative. 

To conclude, the IPCC has compromised the sixth assessment’s most crucial number, rendering it fatally flawed in a manner that exposes the future to climate catastrophe, benefiting no one except the fossil fuel industry. It is basic to risk assessment that the higher number — not the single median number — be applied for future projections. The difference between a climate sensitivity of 3°C against 4.5°C is life and death for our future and all life. (End of Peter Carter's article.)

The following illustrations demonstrate the IPCC's climate sensitivities and the significantly higher climate sensitivities proposed by other qualified climate scientists or climate research organizations.

Despite far higher climate sensitivities being the more appropriate sensitivity choice, once again in their newest, just-released 2021 report, the IPCC uses the lower 3 °C climate sensitivity estimate to appease its supporters in the fossil fuel industry.

What does this climate sensitivity error crisis mean in terms of real climate change consequences and timetables? The tales of two climate change futures very different from each other.

Future one:

Currently, many climate change factors are significantly ahead of the worst-case scenario predictions in the IPCC's AR6 report. Having those many climate factors worse than the IPCC's AR6 report does not even include the climate sensitivity error discussed above.

If we plug what we honestly feel at Job One is the far more likely real climate sensitivity amount of 4.5 from the James Hansen study and adjust the AR6 worst-case scenario predictions, the real and likely climate change future looks like the following. You will not hear this discussed by governments or the media because it would rightly panic the general population, and rightly so.

Calm yourself. As an informed climate change individual, this could be unpleasant.

Here is an AI-created transparent, physics-consistent stress-test that substitutes ECS = 4.5 °C (vs. the IPCC's AR6’s central ECS of 3.0 °C) and shows how temperatures, timelines, and headline consequences would shift under SSP5-8.5.

If Hansen is right, humanity is facing a climate change nightmare, far faster than anyone is saying and far faster than even the wealthiest countries are prepared for. If Hansen is right, this is a very serious climate change consequence and timeline problem for you right now, even without considering what it will do to your children's or grandchildren's future.

(Please note that the Un IPCC in AR6 uses 3 for its ECS calculations.) 

AI used two complementary scalings:

• • Proportional (upper-bound) for late-century/equilibrium-like outcomes: warming scales ~linearly with ECS → multiply by 4.5/3 = 1.5×.

  • Transient-aware for near/mid-century (ocean heat uptake dampens the immediate effect): scale by (ECS_new/ECS_AR6)^β with β≈0.7 (near-term) and β≈0.8 (mid-century).

  • Timing: if warming is higher at each date, milestones arrive sooner. A simple, conservative rule is ~33% earlier(because 1/1.5 ≈ 0.67) measured from a ~2020 baseline.

Think of this as a careful what-if overlay on AR6 SSP5-8.5, not an official IPCC output.

1) Temperatures (SSP5-8.5) with ECS = 4.5 °C

2) Timing shift rule of thumb

For “by YEAR” statements in AR6 SSP5-8.5, bring the year ~33% earlier relative to ~2020:

• • 2050 → ~2040

  • 2080 → ~2060

  • 2090 → ~2067

  • 2100 → ~2073

3) Consequences & new time frames (derived from AR6 SSP5-8.5, adjusted)

How to read these results

• • Temperatures: The table provides explicit recalculated warming projections for the near/mid/late-century under an ECS of 4.5.

  • Timelines: apply the ~33% earlier rule to AR6’s benchmark years (from a 2020 baseline).

  • Impacts: most scale nonlinearly with warming and exposure; the table indicates earlier arrival of AR6’s mid/late-century risk bands plus higher intensity at the exact dates.

To further illustrate the importance of this science controversy, consider the predictions made using the ECS of 1.5 from the study contesting Hansen's work.

The predictions are so different that every government in the world could, in one way or another, significantly reduce its fossil fuel reduction programs and drill baby drill for a long time if the second study is correct.

Future two:

Here is the same AI transparent, “swap-the-ECS” stress test this time with ECS = 1.5 °C in place of AR6’s central 3.0—so you can compare directly to the ECS = 4.5 °C version above. It’s a heuristic overlay on AR6 SSP5-8.5 (not an official re-run of the IPCC models).

How I rescale

• Temperature: scale AR6 best estimates by the ECS ratio. For near/mid-century (ocean heat uptake matters), I use a transient-aware exponent:

  • Near-term β≈0.7, mid-century β≈0.8; late-century ~equilibrium → linear.

  • Ratio r = ECS_new / ECS_AR6. Here r = 1.5/3.0 = 0.5.

• Timing: shift milestone years measured from ~2020 by a factor 1/r.

  • With ECS=1.5 (r=0.5), milestones occur later by ~×2.

  • (Earlier, with ECS=4.5, milestones were ~33% earlier because 1/1.5≈0.67.)

1) Temperatures (SSP5-8.5) under different ECS assumptions

Interpretation: With ECS=1.5, warming is substantially lower at each date; with ECS=4.5 it’s higher.

2) Milestone timing (rule-of-thumb shifts from ~2020)

(Yes, with ECS=1.5 some late-century AR6 milestones slip beyond 2100.)

3) Consequences under ECS=1.5 vs ECS=4.5 (starting from AR6 SSP5-8.5)

HLHI = low-likelihood, high-impact.

Quick takeaways

• With ECS=1.5, SSP5-8.5 still forces hard, but 21st-century realized warming and impacts are markedly lower than AR6’s central case, and many “late-century” AR6 milestones arrive after 2100.

• With ECS=4.5, the opposite holds: higher temperatures sooner and earlier arrival of AR6’s late-century risk bands (often by the 2060s–2070s).

The radical differences between these two ECS calculations should disturb everyone in the climate change science movement due to the significant discrepancies in the outcomes.

Job One for Humanity Editor's Epilogue

The IPCC has fudged the most important number in the most recent sixth assessment, rendering it fatally flawed in a way that exposes the future to endless climate catastrophes, benefiting no one except the fossil fuel industry. It may be assumed that this massive additional source of climate calculation error was the result of the work of government policymakers who sit on the IPCC panel and have the power to approve the final assessment line by line before it is published. 

The question, of course, is how climate scientists could reject the possibility of climate sensitivity above 3°C when the models consistently yield results far higher than 3°C, and when avoiding global climate catastrophe depends on choosing the correct climate sensitivity with the highest and most accurate value. The answer to this question lies in the extraordinary, unique composition of the IPCC panel.

This panel consisted of government representatives who had to approve every line of the assessment before it could be published. This means that the big fossil fuel-producing or supporting governments have not permitted a climate sensitivity to exceed the first 1990 IPCC assessment of 3°C. 

What does this new error mean for your future, and who is most at risk using the IPCC's current climate data for their risk assessments and climate planning

The danger of this severe climate sensitivity calculation error, along with the numerous other IPCC errors (described further below), is that it will lead to a gross underestimation of climate consequences, timelines, and remedies. Yet, the world's governments, intelligence agencies, national reserve banks, the International Monetary Fund, the World Bank, trans-national global corporations, think tanks, risk assessment firms, hedge funds, investment bankers, and insurance companies all use and currently depend upon the IPCC's grossly underestimated summary reports for their climate change planning, strategies, projections, etc. 

This widespread use of the IPCC's seriously unreliable climate consequence predictions, timeframes, and remedial action information means:

1. These critical organizations (and the rest of us) are in for a massive series of unpredicted, expensive, and painful climate consequence shocks within our many economic, political, and social systems, and 

2. The world's foremost organizations have grossly underestimated the actual climate change threat levels, risks, and the timeframes of an already unfolding climate change-driven system collapse and extinction scenario.

3. Due to the ongoing climate sensitivity error, the IPCC's latest climate consequence predictions, timeframes, and remedial action information may be underestimated by as much as 60% or more. (This 60% does not include the effect of the other IPCC errors described further below.)   

Because the underestimation and other errors of the IPCC are so considerable and so extensive, and the foremost organizations we rely upon for stability are using that flawed climate information, humanity and global society are in for a painful, wild, and chaotic ride that will lead us well into mass human extinction and if not fixed soon, total extinction.

Here are more links explaining the decades-long history of the IPCC's many serious climate change calculation errors, making their reports too unreliable for the world's survival 

The immediate survival of humanity is at stake in the climate emergency. We can no longer rely upon the IPCC's climate calculations to create reliable risk assessments or for future climate change-related planning actions.

(Please note: In the links below, we are not attacking or criticizing any of the thousands of hard-working and honest volunteer scientists worldwide who submit their climate research to the IPCC. Instead, we call attention to the IPCC's administrative processes and politicized leadership. They are the ones who alter and contort the real climate science received by these scientists into 5-7 year climate summary reports. Before they are released, these 5-7 year summary reports must get the line-by-line sign-off of the IPCC's major funders, the fossil fuel producing nations, and the fossil fuel-dependent nations.)

Click here to understand the long-term history of the IPCC underestimating the consequences, timeframes, and the needed global fossil fuel reduction targets by as much as 20-40% or more.

Click here to see precisely how the IPCC "cooked the books" and grossly skewed the current IPCC global fossil fuel reduction calculations by including unproven and non-existent "carbon sucking unicorn" technology into their projections. 

Click here to see the IPCC's Perfect Day problem with its computer climate modeling.

Click here to see the eleven key climate change tipping points that have been mostly excluded from the IPCC calculations on how much fossil fuel use we must reduce each year globally. 

Click here to see the four key reasons why the IPCC's 26 global climate conferences have failed to produce results or legitimate global fossil fuel reduction targets.

Click here to see the IPCC's huge atmospheric methane calculation problem.

Click here to see the latest 2022 IPCC climate change summary report on the critical climate sensitivity error. Due to this ongoing climate sensitivity error alone, the IPCC's latest climate consequence predictions, timeframes, and remedial action information may be underestimated by as much as 25% or more. (This 25% does not include the effect of the other IPCC errors described in the links just above.) 

Click here to view a new study revealing that the IPCC omits several crucial climate system factors from its computer climate models. Those missing factors result in incorrect and distorted outcomes. This February 2022 paper strongly refutes the absurd IPCC claim that the decline in Arctic sea ice melt is reversible. It is not reversible, and that is a monster problem for humanity's weather, seasonal climate, and future!

The decades of error, miscalculation, and polarization problems linked above also mean that the IPCC is an unreliable partner for truthful and accurate climate change information. Their climate consequence predictions, timeframes, and remedial action information are grossly underestimated by 30-60% and possibly more. 

Generally, if the IPCC currently predicts that a certain climate consequence will occur or that action must be taken within ten years, it is more likely to happen within 5-6 years. For example, if the IPCC states that we must reduce global fossil fuel use by 45% by 2030, the actual reduction will be 75% by 2025-2026. Start discounting everything coming out of the IPCC by 50% to compensate for all of their decades of errors, miscalculations, and polarization, and you will not be too far from the truth, which they are desperately trying to hide or disguise.

At the minimum, we hope that by the time you read this article and its documentation, you too will adopt the general rule of thumb that, whatever the IPCC tells you about the coming climate change consequences, timeframes, and remedies, will be underestimated by at least 20-40%! 

What can you do about the climate emergency?

Click here and select the action plan that is best for your situation and resources.

Here is more information from Wikipedia on this issue:

In preparation for the 2021 IPCC Sixth Assessment Report, a new generation of climate models was developed by scientific groups around the world.^[107][108] Across 27 global climate models, estimates of a higher climate sensitivity were produced. The values spanned 1.8 to 5.6 °C (3.2 to 10.1 °F) and exceeded 4.5 °C (8.1 °F) in 10 of them.^[109][110] The estimates for equilibrium climate sensitivity changed from 3.2 °C to 3.7 °C, and the estimates for the transient climate response changed from 1.8 °C to 2.0 °C.^[111] The cause of the increased ECS lies mainly in improved modelling of clouds. Temperature rises are now believed to cause sharper decreases in the number of low clouds, and fewer low clouds mean more sunlight is absorbed by the planet and less reflected to space.^{[111][109][112][113]}

Remaining deficiencies in the simulation of clouds may have led to overestimates,^[114] as models with the highest ECS values were not consistent with observed warming.^[115] A fifth of the models began to 'run hot', predicting that global warming would produce significantly higher temperatures than is considered plausible.^[116][117] According to these models, known as hot models, average global temperatures in the worst-case scenariowould rise by more than 5 °C above preindustrial levels by 2100,^[118] with a "catastrophic" impact on human society.^[119] In comparison, empirical observations combined with physics models indicate that the "very likely" range is between 2.3 and 4.7 °C. Models with a very high climate sensitivity are also known to be poor at reproducing known historical climate trends, such as warming over the 20th century or cooling during the last ice age.^[117] For these reasons the predictions of hot models are considered implausible, and have been given less weight by the IPCC in 2022.^[114]