RCP8.5 Has Been Dropped: What It Means — and What It Doesn’t

“The United Nations TOP Climate Committee just admitted that its own projections (RCP8.5) were WRONG! WRONG! WRONG!” – US President, Donald J. Trump, May 16, 2026 - https://truthsocial.com/@realDonaldTrump/posts/116586488927495029

The developers of the greenhouse gas emissions scenarios for the IPCC’s next assessment report (AR7) have officially dropped RCP8.5 – the high-emissions pathway long treated as a de facto “business-as-usual” case (Van Vuuren et al. 2026).

We at CERES were among the first to criticize the use of RCP8.5 in the peer-reviewed literature (Connolly et al. 2020) and welcome this decision. But, while President Trump’s description of RCP8.5 as “WRONG! WRONG! WRONG!” has a kernel of truth beneath the hyperbole, the real story is more nuanced – less dramatic, but scientifically important.

Dropping RCP8.5 is a good step in the right direction. However, the IPCC still look to be set to continue their overreliance on computer model projections that are highly sensitive to changes in greenhouse gas concentrations. So, while their “business-as-usual” projections will probably be a bit less “hot” than before, unfortunately they still look set to be producing more “alarm-as-usual”.

In this essay, we discuss what RCP8.5 actually was, why it was problematic from the start, and what this change does – and does not – mean.

What exactly is RCP8.5 and why was it so significant?

According to current climate computer models, the main driver of past and future climate change is the concentration of “greenhouse gases” in the atmosphere.

Most of these greenhouse gases are naturally-occurring. However, many key human activities (energy usage, agriculture, etc.) also are associated with greenhouse gas emissions. For this reason, the UN and others – especially the computer modellers – have been insisting for decades that humans should be causing “anthropogenic global warming” (AGW) from our greenhouse gas emissions. [“anthropogenic” = is a more ‘sciencey’-sounding word for human-caused].

In fact, as Dr. Roger Pielke Jr. pointed out in a key 2005 paper (R. A. Pielke 2005), through their “Framework Convention on Climate Change” (UN FCCC), the UN has – at each of their annual UN Conference of the Parties (COP) meetings – been effectively defining all “climate change” as human-caused by definition for more than 30 years. These COP meetings are the annual UN gatherings where politicians and NGOs gather from around the world in a chosen city to discuss climate change policies.

This brings us to the so-called RCP scenarios – “Representative Concentration Pathways” (Meinshausen et al. 2011). For the IPCC’s 5^th Assessment Report, the computer modellers had been given a choice of 4 different “projections” for what greenhouse gas emissions (and concentrations) might be over the coming centuries. Each scenario was given a number which represented the theoretical extra “radiative forcing” that greenhouse effect models said the extra greenhouse gases would have by the end of the 21^st century – in units of Watts per square meter: 8.5, 6.0, 4.5 or 2.6.

In section 5.3 of Connolly et al. (2020), we discuss what scientific merit these theoretical “radiative forcing” calculations have for understanding the climate. But, within the climate modelling community, the size of this final theoretical value is the primary determinant of how much “global warming” would occur. So, the various scenarios were named based on that number: RCP8.5, RCP6.0, RCP4.5 and RCP2.6.

When you looked in detail at the emissions scenarios, RCP6.0, RCP4.5 and RCP2.6 all implied that there were major policy interventions to reduce greenhouse gas emissions during the 21^st century. In contrast, RCP8.5 was the only scenario that didn’t assume major interventions.

Perhaps for this reason, the climate modellers began relying on the RCP8.5 scenario as the “business-as-usual” scenario. This meant that thousands of papers describing simulations of “the climate changes that will happen if we don’t do something urgently” ended up being published based on this RCP8.5 scenario – i.e., the one that has now been dropped.

Why was RCP8.5 unrealistic from the beginning and why has it been officially dropped?

When we wrote our paper in 2020, we noted that a few others had criticised the use of RCP8.5 as “BAU”. Ritchie and Dowlatabadi (2017b, 2017a) dug into the economics of the scenario and discovered the RCP8.5 assumed that societies would dramatically increase the use of coal over the next century – so much so that the scenario suggested that coal usage would burn more than 5 times the known reserves of coal!

They warned that this was ludicrous – but since they were writing in academic journals, the exact language they used was a lot milder:

“Accounting for this bias indicates RCP8.5 and other ‘business-as-usual scenarios’ consistent with high CO2 forcing from vast future coal combustion are exceptionally unlikely.” (Ritchie and Dowlatabadi 2017b).

Prof. Ritchie was joined in his criticism by others, including Prof. Pielke Jr. (who we met earlier), e.g., (R. A. Jr. Pielke and Ritchie 2021; Burgess et al. 2020).

Meanwhile, the scenario was also criticised from a completely different angle: Hausfather and Peters (2020) argued that the scenario was unrealistic because they believed governments were transitioning to lower emissions policies. They therefore insisted that “business-as-usual” should consider the recent trends in policies to be “business-as-usual”.

Ultimately, the recent decision to drop RCP8.5 from the next report seems to have taken Hausfather & Peter’s arguments as their primary justification:

“the CMIP6 high emission levels (quantified by SSP5-8.5) have become implausible, based on trends in the costs of renewables, the emergence of climate policy and recent emission trends” – Van Vuuren et al. (2026)

Although, they did also cite Ritchie & Dowlatabadi’s criticisms as a key factor in their decision.

However, our criticism of RCP8.5 in Connolly et al. (2020) came from a different angle…

What was our goal in Connolly et al. (2020)?

After the 2015 COP meeting in Paris, France, a highly influential agreement was signed called the Paris Agreement. All of the nations agreed to,

“[hold] the increase in the global average temperature to well below 2 °C above preindustrial levels and pursuing efforts to limit the temperature increase to 1.5 °C above preindustrial levels” – UN Paris Agreement (UNFCCC 2016)

Parsing this convoluted statement and what it means was the main theme of our Connolly et al. (2020) paper. Essentially, they seemed to be saying that governments around the world would have to collectively implement major policy changes to keep global warming “below 2 °C above preindustrial levels”. But what did that mean?

What policies did they need to implement? How much “global warming” would be expected without these policies? What did they mean by “pre-industrial levels” – there have been many warm and cold periods over the millennia – which one did they consider “pre-industrial”?

We realised that this widely-promoted “agreement” didn’t mean anything unless you had some sort of answer for those questions.

So, for Connolly et al. (2020), we decided to try and answer a fundamental question that the Paris Agreement needed answered before the agreement could mean anything other than waffle:

“How much human-caused global warming should we expect with Business-As-Usual (BAU) climate policies?”

If we don’t know the answer to that, then how could policymakers figure out what to do to meet their nebulous “goal”.

When we tried to answer that question, we realised that the answer actually depends on four sub-questions:

1. How much greenhouse gases will we emit if we continue current trends?

2. How much of those emissions will remain in the atmosphere?

3. How much of the warming already observed is caused by humans?

4. How strongly do greenhouse gases warm the planet?

In our paper – very long, but methodical and systematic – we went through each of these questions, step-by-step. For each step, we surveyed the scientific literature to identify the different perspectives out there, looked at the available data, considered the various assumptions that could be made. We then compiled a best-estimate of what we could expect if trends continued “business-as-usual”, i.e., based on current trends.

We warned however that this was a multi-disciplinary problem,

“With each of these questions, there is considerable debate in the scientific literature. However, the relevant literature for each subject comes from quite different academic disciplines. The first question is typically addressed by economists, political scientists, environmental governance researchers, etc. The second question is mostly the realm of biologists, ecologists, geochemists, oceanographers, etc. The third and fourth questions are both climate science problems, but even within these topics, there are separate bodies of literature from, e.g., computer modelling research groups, groups evaluating climate records, statisticians evaluating results from a meta-analysis perspective, etc.

[…] However, we suggest that unless the scientific debate over all four of these questions are simultaneously considered, it is unlikely that truly satisfactory answers will be achieved to the over-arching question, “How much human-caused global warming should we expect with Business-As-Usual (BAU) climate policies?” – Connolly et al. (2020), p3.

Q1. How much greenhouse gases will we emit if we continue current trends?

We saw above that much of the debate over RCP8.5 has focused on how policies might or might not change in the future. But, in our opinion, this goes against the very definition of “business-as-usual”. Instead, we reasoned, why don’t we simply define “business-as-usual” emissions as if the emissions were to continue business-as-usual?

Rather than speculating on complicated potential “scenarios” on “what if” and “what if not”, we said, why don’t we simply look at the trends in emissions over the past 50-70 years and assume that these trends would continue “business-as-usual”?

What happens when we compare this BAU emissions scenario (grey envelope with black dashed line in the graphs below) to the RCP scenarios? For simplicity, let’s just consider CO2 emissions (in the paper, we also consider the other two main anthropogenic greenhouse gases, i.e., CH4 and N2O).

As soon as we plotted the graph below, it was obvious that the RCP8.5 scenario was never “business-as usual”. Notice how the RCP8.5 scenario rapidly deviates above the actual BAU envelope and stays above it?

For us, RCP8.5 was clearly not a “business-as-usual” scenario. Nor were any of the other RCP scenarios offered to the modellers.

Bizarrely, the very first IPCC report had already developed in 1990 (36 years ago) as “Scenario A” a business-as-usual projection that matched remarkably well with our empirical fit that we developed 30 years later in our 2020 paper. See below:

Why didn’t the IPCC modellers simply stick to that 36 year old “Scenario A” as their “business-as-usual”? I don’t know. Cynics might suggest that it wasn’t giving results that were “hot enough” – maybe the computer models wanted to “spice up” their simulations with some extra “warming”? Or maybe, the older Scenario A just seemed too old-fashioned?

But, whatever the reason, the extra warming the RCP8.5 simulations added to the mix were like crack cocaine to the modellers. It was routinely treated as if the scenario were “business-as-usual”.

For the 6^th Assessment Report (AR6, 2021), the scenario groups tried to add in a bit more balance and introduced intermediate scenarios into the updated “SSP/RCP” scenarios, e.g., “SSP3-70 (Baseline)” with a 2100 Radiative Forcing of 7.0 instead of 8.5. But, they left the 8.5 scenario in as a second “baseline”: “SSP5-85 (Baseline)”. And, so, the 8.5 scenarios continued to dominate the computer model simulations of “business-as-usual”.

However, while much of the recent discussion about RCP8.5 has focused on what emissions we can expect if society continues business-as-usual, in our paper, we emphasised that this was just the first step. The next question is establishing how much of those emissions should we expect to remain in the atmosphere under business-as-usual…

Q2. How much of those emissions will remain in the atmosphere?

Almost continuous direct measurements of the average concentration of CO2 in the atmosphere have been carried out at Mauna Loa, Hawai’i since 1958. These measurements have shown a long-term increase from about 0.031% of the atmosphere in 1958 to about 0.043% today.

Since these are such tiny percentages, typically, people refer to CO2 concentrations in terms of parts per million by volume (“ppmv” or sometimes “ppm”). But, we’ve found that people have a better feeling of what the numbers mean when we use percentages. So, in the graph of the data below, we provide the values in ppmv on the left and the equivalent values in % on the right.

There have been several attempts to try and estimate how CO2 has changed in the atmosphere in the years before the Mauna Loa record. The IPCC and many others rely on the Antarctic ice core estimates. These imply that for the last few thousand years, CO2 only varied a tiny amount – between 0.027 and 0.029% - see the grey band in the figure above.

The fact that human-caused CO2 emissions have been increasing and CO2 concentrations have also been increasing has convinced many that we just need to focus on the emissions part. But, when you convert the annual human-caused (“anthropogenic”) emissions into the expected increase in CO2 concentrations, a problem arises.

As can be seen from the graph below, the actual change in CO2 concentrations (“observed change” in green) is much noisier and much less than the human-caused emissions (“anthropogenic emissions” in red)!

Within the scientific literature, the fraction of the emitted CO2 that remains in the atmosphere is known as the “airborne fraction”. This is simply the green line divided by the red line. It’s plotted below:

We can see that on average only about 44% (i.e., airborne fraction = 0.44) of the emitted CO2 remains in the atmosphere. But, the greenhouse effect theory is based on atmospheric concentrations, not emissions. So, if you want to predict how much human-caused global warming to expect under BAU, then you need to convert the expected emissions into the expected concentrations. Hence, you also need to estimate how the airborne fraction would change.

For our analysis, we decided that the most logical assumption to make is to assume that “business-as-usual” conditions means that the airborne fraction will also continue “business-as-usual” as it has since measurements began in 1958. However, when we analysed the RCP scenarios, we discovered that the RCP scenarios do NOT make that assumption – see graph below.

While all of the RCP scenarios start off with an airborne fraction similar to the historical average, several of them show major changes in airborne fraction during the 21^st century that are not “business-as-usual”, i.e., they deviate from the grey envelope above.

Significantly, we can see that RCP8.5 had baked in a long-term increase in the airborne fraction throughout the century. This meant that as well as projecting emissions far more than “business-as-usual”, the scenario also projects that the concentrations would increase even more than expected. Even for RCP6.0, the scenarios projected an increasing airborne fraction.

So, in the end, we found that our simple semi-empirical “business-as-usual” projections for future concentrations were much less than RCP8.5 – arguably much closer to RCP6.0 – see below.

So, yes, the RCP8.5 scenario should NEVER have been treated as “business-as-usual”. And, it’s good that they have finally dropped it from their new scenarios.

However, in our paper, we went further. The Paris Agreement was supposed to be specifically about limiting “global warming” to less than 2℃. But, the RCP scenarios just tell us what emissions and concentrations to expect under different scenarios. This doesn’t tell us what global temperature changes to expect. So, that led us onto our next question…

Q3. How much of the warming already observed is caused by humans?

The Paris Agreement said that nations would work to keep global warming “well below 2 °C above preindustrial levels”. But, what does “preindustrial levels” mean?

As Pielke Jr. (2005) had shown, the UN’s Framework Convention on Climate Change definition of “climate change” explicitly ignored any natural changes in the climate. But, paleoclimate studies using tree rings, lake sediments, and other “temperature proxies” have shown that the Earth has gone through different periods of global warming and global cooling over the past thousand years and earlier – long before the Industrial Revolution. So, defining “preindustrial levels” is very subjective – e.g., do you choose the end of the “Little Ice Age” in the 19^th century, or do you choose the Medieval Warm Period at the time of the Vikings?

Temperature proxy reconstructions are the subject of considerable ongoing scientific debate. But, we showed that regardless of whether you choose “the hockeystick graph” or you go with a reconstruction showing a warm Medieval Warm Period, the idea that there was a single constant “global temperature” for “preindustrial levels” is foolish – see below:

Essentially, the UN’s obsession to define all climate change as “human-caused” by definition was unscientific. If we want to get a scientific answer to our question, we need to consider the possibility that some or all of the global warming since the end of the Little Ice Age might have nothing to do with human-caused greenhouse gas emissions.

The Paris Agreement forgot to do that. So, this left the Agreement as utterly meaningless since they had forgotten to account for naturally-occurring global temperature changes. The Paris Agreement was supposed to be about policymakers implementing policies that could reduce the rates of human-caused global warming. But, by definition, we humans cannot influence the rates of natural global warming or global cooling. So, the poor phrasing of the Agreement meant that the success or failure of any potential policies could be completely undone by the forces of nature!

In our paper, we proposed a simple solution. We simply assume that the text in the Paris Agreement meant to say human-caused global warming, “well below 2 °C above preindustrial levels”. We then can just focus on any global warming that is due to increases in atmospheric greenhouse gas concentrations from human-caused emissions.

This gives us a relatively objective metric for defining “preindustrial levels” – instead of worrying about preindustrial global temperatures, we can look at preindustrial levels of greenhouse gas concentrations.

As we saw earlier, the Antarctic ice core estimates of preindustrial levels are very well defined, e.g., CO2 was within the range 0.027-0.029%. That said, as we discussed in our paper, the other published estimates that have been attempted (Greenland ice cores, the size of “stomatal pores” on the leaves of fossilized plants and compiling individual measurements made by scientists since the late-19^th century) all imply a much greater natural variability in CO2 concentrations. We suggested that these surprisingly different scientific findings should be explored with more of an open mind.

But, for our analysis, we explicitly assumed that the IPCC-preferred estimates, i.e., Antarctic ice core estimates, are accurate. Hence, the amount of “human-caused global warming” we would expect under business-as-usual depends on the increase of greenhouse gas concentrations above these Antarctic ice core estimates.

But, we still had one more question to answer…

Q4. How strongly do greenhouse gases warm the planet?

The final question, but perhaps the most important and controversial – how much global warming should we expect for a given increase in greenhouse gases? This is typically discussed in terms of the so-called “climate sensitivity”, i.e., how much global warming should be expected for a doubling of carbon dioxide concentrations?

As we will see, while this sounds like a fairly basic property that we should know before we start debating over questions such as whether we should try to “limit global warming” to 1.5℃ or 2℃, to this day, scientists differ wildly over what value they think this “climate sensitivity” to CO2 is.

The debates began with the different computer modellers. In the late-1970s, climate computer modellers would try to model the effects of increasing carbon dioxide by running a simulation with current concentrations and then running another simulation that was identical except with double the concentration.

They would then compare the average global temperatures from both simulations. The extra warming in the doubled model world became known as the “equilibrium climate sensitivity” (ECS), but each computer model gave a different value. The differences were substantial. The influential 1979 “Charney Report” (Charney 1979) concluded that the ECS could be any value between 1.5℃ and 4.5℃.

That’s quite a wide range! The highest value predicted three times as much global warming as the lowest.

But, you are probably thinking, “well, that was 1979 – computers were very primitive and climate science was still a relatively young field – they have probably refined their estimates now…”. So, what did the IPCC’s 5^th Assessment Report (2013) say? They concluded that … the ECS was “likely” to between 1.5℃ and 4.5℃! The exact same range as in 1979. And that was the “likely” range. The IPCC conceded that the true value could potentially be either higher or lower!

Knutti et al. (2017) summarised the problem with the following chart showing the range of ECS estimates that have been published in the scientific literature:

Various estimates of the “equilibrium climate sensitivity” (ECS) climate sensitivity. Adapted from Figure 2 of Knutti et al. (2017)

Have a look at the chart yourself – which value (if any) is correct? If you’re feeling like a deep dive, you could also read through the references beside each estimate to see how they calculated their estimates.

Similar debates have been ongoing since the 1980s over an alternative measure of the climate sensitivity called the “Transient Climate Response” (TCR).

Hopefully you can see that if scientists are still disagreeing wildly over how “sensitive” global temperatures are to a doubling of CO2, then calculating “how much human-caused global warming” we should expect under business-as-usual is still up in the air.

So, for our final analysis, rather than trying to decide what the true ECS (or TCR) is, we considered a range of possible values. For each value, we calculated how much human-caused global warming we should expect under business-as-usual up to 2100.

Below are the results for the ECS values – see the paper for the equivalent projections for TCR.

A striking result is that if the ECS is greater than 4℃, then the Paris Agreement to keep human-caused global warming below 2℃ would be broken within 35-45 years if we continue business-as-usual. But, if the ECS is less than 2℃, then the Paris Agreement would be kept for the entire 21^st century even if we continue business-as-usual. Yet, the IPCC reports were saying that the “likely” range of potential values for ECS is even wider, i.e., anything from 1.5 to 4.5℃. We found similar results for TCR.

This led to our final conclusion:

“Therefore, the current Intergovernmental Panel on Climate Change (IPCC) “likely” range estimates for TCR of 1.0 to 2.5℃ and ECS of 1.5 to 4.5℃ have not yet established if human-caused global warming is a 21st century problem.”

Why dropping RCP8.5 is an important step, but not the end of the UN panicking about climate change?

So, in the end, what is the significance of RCP8.5 being dropped from the IPCC’s scenarios?

It is a good step in the right direction – despite Van Vuuren et al. (2026)’s claims that they dropped RCP8.5 because it “has become implausible”, as our analysis showed in 2020 – and as others have shown (Ritchie and Dowlatabadi 2017b, 2017a; Burgess et al. 2020; R. A. Jr. Pielke and Ritchie 2021) – RCP8.5 was never plausible as a “business-as-usual” scenario. Yet, because it was the only RCP scenario that didn’t explicitly include major “climate mitigation” policies for the 21^st century, it became by default the scenario used by the computer modelling groups to simulate “business-as-usual” climate changes.

However, unfortunately, we fear that this is only a small step in the right direction. The IPCC still looks set to be relying on the current climate computer models for their “climate change projections”. But, as we discuss in the paper, most of the highest estimates of the “climate sensitivity” come from the computer models. So, even using a more realistic “business-as-usual” emissions scenario, their models are still going to simulate dramatic “human-caused global warming”.

Still, at least it is a step in the right direction.

References

• Burgess, Matthew G., Justin Ritchie, John Shapland, and Roger Pielke. 2020. “IPCC Baseline Scenarios Have Over-Projected CO2 Emissions and Economic Growth.” Environmental Research Letters 16 (1): 014016. https://doi.org/10.1088/1748-9326/abcdd2.

• Charney, Jule. 1979. Carbon Dioxide and Climate: A Scientific Assessment 1979. National Research Council. https://doi.org/10.17226/12181.

• Connolly, Ronan, Michael Connolly, Robert M. Carter, and Willie Soon. 2020. “How Much Human-Caused Global Warming Should We Expect with Business-As-Usual (BAU) Climate Policies? A Semi-Empirical Assessment.” Energies 13 (6): 1365. https://doi.org/10.3390/en13061365.

• Hausfather, Zeke, and Glen P. Peters. 2020. “Emissions – the ‘Business as Usual’ Story Is Misleading.” Nature 577 (7792): 7792. https://doi.org/10.1038/d41586-020-00177-3.

• Knutti, Reto, Maria A. A. Rugenstein, and Gabriele C. Hegerl. 2017. “Beyond Equilibrium Climate Sensitivity.” Nature Geoscience 10 (10): 727–36. https://doi.org/10.1038/ngeo3017.

• Meinshausen, Malte, S. J. Smith, K. Calvin, et al. 2011. “The RCP Greenhouse Gas Concentrations and Their Extensions from 1765 to 2300.” Climatic Change 109 (1): 1. https://doi.org/10.1007/s10584-011-0156-z.

• Pielke, Roger A. 2005. “Misdefining ‘Climate Change’: Consequences for Science and Action.” Environmental Science & Policy, Mitigation and Adaptation Strategies for Climate Change, vol. 8 (6): 548–61. https://doi.org/10.1016/j.envsci.2005.06.013.

• Pielke, Roger A. Jr., and Justin Ritchie. 2021. “How Climate Scenarios Lost Touch With Reality.” Issues in Science and Technology, July 26. https://issues.org/climate-change-scenarios-lost-touch-reality-pielke-ritchie/.

• Report of the Conference of the Parties on Its Twenty-First Session, Held in Paris from 30 November to 13 December 2015. Addendum. Part Two: Action Taken by the Conference of the Parties at Its Twenty-First Session. | UNFCCC (2016). https://unfccc.int/documents/9097.

• Ritchie, Justin, and Hadi Dowlatabadi. 2017a. “The 1000 GtC Coal Question: Are Cases of Vastly Expanded Future Coal Combustion Still Plausible?” Energy Economics 65 (June): 16–31. https://doi.org/10.1016/j.eneco.2017.04.015.

• Ritchie, Justin, and Hadi Dowlatabadi. 2017b. “Why Do Climate Change Scenarios Return to Coal?” Energy 140 (December): 1276–91. https://doi.org/10.1016/j.energy.2017.08.083.

• Van Vuuren, Detlef P., Brian C. O’Neill, Claudia Tebaldi, et al. 2026. “The Scenario Model Intercomparison Project for CMIP7 (ScenarioMIP-CMIP7).” Geoscientific Model Development 19 (7): 2627–56. https://doi.org/10.5194/gmd-19-2627-2026.

Further reading

• Hausfather, Peters & Foster. Substack, May 18, 2026. https://www.theclimatebrink.com/p/on-the-death-of-rcp85. They agree RCP8.5 should have been dropped but dispute Trump’s assertion that it was “wrong”. They argue that RCP8.5 was dropped because society has been reducing their emissions trajectory through green policies.

• Pielke Jr. Substack, May 18, 2026. https://rogerpielkejr.substack.com/p/no-rcp85-did-not-become-implausible. Pielke argues that RCP8.5 was never plausible from the beginning and it has nothing to do with recent policies.

• Connolly, Connolly & Soon. Apr 15, 2021. https://www.ceres-science.com/post/how-much-global-warming-should-we-expect-under-business-as-usual-policies. An earlier summary of our Connolly et al. (2020) paper.