Global warming, climate change, all these things are just a dream come true for politicians. I deal with evidence and not with frightening computer models because the seeker after truth does not put his faith in any consensus. The road to the truth is long and hard, but this is the road we must follow. People who describe the unprecedented comfort and ease of modern life as a climate disaster, in my opinion have no idea what a real problem is.
More observational evidence emerges showing CO2’s effects are too small to drive climate.
The oft-cited Feldman et al. (2015) paper proposes to isolate the CO2 impact by only considering a “clear-sky” atmosphere at two sites: the North Slope of Alaska and the Southern Great Plains (USA). In other words, that study can only claim to assess what occurs in an imaginary atmosphere where clouds do not exist – even though clouds are present about 60-70% of the time in the real-world atmosphere.
Results indicated that CO2 enhances the downwelling longwave radiative forcing (DLRF) trend, the greenhouse effect, by just 0.2 W/m² per decade (accompanying a 22 ppm CO2 increase from 2000 to 2010).
But a 2025 paper quietly published in Nature also assessed the contributors to the DLRF trend from 1996-2018 at the Southern Great Plains, even extending their measurements to all land surfaces across the globe from 60°S to 60°N.
But instead of employing only a simulated atmosphere where clouds do not exist, Liu and colleagues provided the all-sky values. So, unlike the Feldman paper, they employed the real-world atmosphere which have clouds contributing to (and dominating) the DLRF trend.
They found observed trends in downwelling longwave show the cloud DLRF contribution actually serves to reduce the greenhouse effect impact by -0.77 to -1.77 W/m² per decade.
Since the CO2 contribution enhances the trend by only 0.2 W/m² per decade, clouds therefore have been observed to easily outclass and even nullify (net) the effect of CO2 increases.
The tiny “finger printed” (FP) decadal effect of CO2 in a real-world, all-sky atmosphere is illustrated (red bar) in the DLRF trend (W/m² per decade) graph. Notice how insignificant the CO2 contribution is compared to the effect of clouds (gray bar).
Perhaps this is why Feldman and colleagues chose to use an imaginary-world, clear-sky-only atmosphere instead of a real-world, all-sky atmosphere.
RCP8.5 was designed as a high-end (roughly 90th percentile) exploratory scenario, not a central “business-as-usual” projection. Its divergence from observed trends stems primarily from unrealistic internal assumptions (especially massive coal expansion), evident well before major post-2015 policy accelerations or renewables cost drops fully took effect.
RCP8.5 was never a plausible “business-as-usual” (BAU) or no-policy baseline; it was a high-end exploratory scenario from the start, and evidence shows it was already diverging from reality based on its own assumptions, not primarily due to later climate policies.
RCP8.5 (developed around 2011) was designed as one of four Representative Concentration Pathways for climate modeling. It leads to ~8.5 W/m² radiative forcing by 2100, corresponding to high GHG concentrations and roughly 4–5°C warming (with a wide range).
RCP8.5 was designed as a high-end (roughly 90th percentile) exploratory scenario, not a central “business-as-usual” projection. Its divergence from observed trends stems primarily from unrealistic internal assumptions (especially massive coal expansion), evident well before major post-2015 policy accelerations or renewables cost drops fully took effect.
Recent developments (as of 2026) reinforce this: the CMIP7 ScenarioMIP framework for IPCC AR7 has effectively retired RCP8.5/SSP5-8.5 as a core scenario. The new “High” scenario sits lower (around RCP6-7 range), acknowledging that extreme high-end paths have become implausible based on renewables trends, emission data, and socioeconomics—not solely policy “success.”
No, RCP8.5 did not become implausible because of climate policy. Today, I explain why. The Honest Broker has the story.
In the past several weeks prominent climate researchers have defended RCP8.5 as a scenario that a decade ago plausibly described where the world was headed, but thanks to their warnings, the world’s policy makers responded with implementation of climate policies that have now made RCP8.5 implausible.
The implication of these claims is that the world was once headed for ~4.8C temperature increase by 2100 and now it is ~2.7C — a huge decrease.
For example:
Detlef van Vuuren,1 lead author of the ScenarioMIP paper released last month, explained to The Australian that RCP8.5 had,
“become implausible, based on trends in the costs of renewables, the emergence of climate policy and recent emission trends.”
Zeke Hausfather, a climate scientist at Stripe and a frequent, friendly intellectual sparring partner of mine, also framed RCP8.5 as once plausible but now implausible due to climate policy successes:
“[I]t is incontrovertible that rapid cost declines, investment in, and deployment of clean energy technologies in the past 15 years have changed the plausible scenarios for fossil fuel use later in this century. These new scenarios reflect this success.”2
Robert Vautard, Co-Chair of IPCC Working Group I for AR7, also framed the retirement of RCP8.5 as the result of successful climate policies:
“Previous “high scenarios” started in 2015 and assumed no climate policies, but there ARE now many climate policies in many countries, developed in particular with the Paris Agreement signed in 2016 (sic), and before. . . it shows that climate mitigation policies do consistently reduce global warming.”
Each of these framings rests on a common logic: RCP8.5 once described a plausible trajectory; subsequent policy progress and technology cost trends moved the world away from it; therefore the scenario became implausible.3
This story, were it true, would be incredibly convenient for the climate science community. Rather than introducing a flawed scenario to the world that dominated climate science and policy for more than a decade — and then stubbornly defending it — this retelling characterizes the climate science community as near-infallible and heroic.
This story is not true. RCP8.5, and other extreme scenarios, were never plausible.
Scenario plausibility is determined by what theory and evidence supports at the time a scenario is created, not simply by whether the world eventually moved toward or away from the projections that emerge from that scenario.
That means that a scenario that deviates from how the world actually evolved was not necessarily retroactively implausible at the time it was created. A scenario built on assumptions inconsistent with available theory and evidence is implausible at construction, regardless of whether subsequent events confirm or contradict its projections.
“a coherent, internally consistent, and plausible description of a possible future state of the world.”
Scenarios are explicitly “not predictions.” But they must be consistent with theory and evidence.
Any projection built on scenario assumptions that contradict available theory and evidence is invalid from the start, regardless of what happens next. Further, scenarios are not predictions, and a family of scenarios does not describe a probability distribution of expected futures. Much wisdom on scenarios has been lost since IPCC SRES in 2000.
Below, I discuss three assumptions of RCP8.5 that made it implausible from the start (ignoring other implausible assumptions, like its incredible population growth rates):
Reliance on a flawed theory for the dramatic expansion of coal energy;
A corresponding rapid increase in coal-to-liquids, displacing petroleum;
A necessary slowdown in technological improvements in solar energy technology.
Let’s take a look at each.
First, RCP8.5 required burning coal at an implausible rate. Coal is the most carbon intensive fossil fuel, and huge amounts needed to be burned to reach the high forcing level that was assigned to the most extreme RCP scenario.
Recall that under the RCPs radiative forcing levels for 2100 were chosen first, and only later were integrated assessment modelers assigned the task of figuring out how those levels could be reached. RCP8.5 required implausible socio-economic assumptions to meet its preassigned design criteria. Unfortunately, the scenario develoipment community yet to learn that socio-economics should come first.
The figure above, from Ritchie and Dowlatabadi 2017 (RD17), shows that RCP8.5 assumed ~8x increase in primary energy generation from coal. In fact, the entire envelope of assumed future coal consumption across the RCP and SSP scenarios shows an increase in coal — based on a single theory, characterized by RD17 as a “return to coal.”
RD17 explain that the MESSAGE integrated assessment model that generated RCP8.5 applied no constraint from geological reality, and simply assumed that the massive amounts of coal it required would be available. The scenario extrapolated 2000s Chinese coal growth rates and assumed the physical resource base would accommodate whatever the consumption assumption required irrepective of real-world constraints.
The figure below shows that coal consumption as a proportion of the global energy mix started declining around 2013, while RCP8.5 had it steadily increasing. The reason for the divergence between reality and RCP8.5 was not climate policy, but rather a false assumption baked into the scenario from the start.
RCP8.5 — and indeed all of the RCP and SSP scenarios — had a single point of failure in its assumption of a return-to-coal. This assumption alone settles the question of plausibility. A scenario requiring five times proven coal reserves is not plausible by any standard.
In a new study scientists have acknowledged the modeled assumptions forecasting nature’s response to the presumed human-driven radiative forcing of ocean heat uptake, thermal expansion, and sea level rise rates do not align well with observations from recent decades.
Fundamental assumptions in projections of alarming, CO2-induced global warming in the coming decades are undermined by a new long-term energy budget analysis.
In a new study scientists have acknowledged the modeled assumptions forecasting nature’s response to the presumed human-driven radiative forcing of ocean heat uptake, thermal expansion, and sea level rise rates do not align well with observations from recent decades.
The apparent misalignment is especially pronounced during 2000-2020 (Fig. 2 in the image), as the assumed uptick in radiative forcing (which is said to be a consequence of rising human CO2 emissions) was not accompanied by a sharp increase in Earth’s energy imbalance (EEI). Instead, the assumed forcing values are 50% greater than EEI estimates during this period.
When the entire 1880-2020 period is considered, it is notable that the fraction of forcing that delivers heat energy to the Earth has been (much) smaller in recent decades than in the first half of the 20th century despite the assumed cause of the forcing (human CO2 emissions) being several times larger since about 1980.
Consider that from 1910 to 1945 human CO2 emissions remained relatively flat at ~1 GtC/year, but then emissions rose to ~6 GtC/year by 1990 and to nearly 10 GtC/year by the 2010s. Despite this dramatic increase in the assumed radiative forcing from CO2 emissions, the heat uptake (Fig. 1 and S6), thermal expansion (Fig. S17), and sea level rise rates (Fig. S17) were nearly as pronounced in 1910-1945 as they were from 1980-2010. In fact, there was a decline in the heat uptake, thermal expansion, and sea level rise rates from 1945 to 1975 despite the coincident sharp increase in CO2 emissions during this period.
“We find two distinct phases in the global energy budget. In 1880–1980, Earth’s energy imbalance closely followed the radiative forcing. After 1980, however, Earth’s energy imbalance increased at a slower rate than the forcing; in 2000–2020, the imbalance amounted to less than 50% of the forcing.”
Since nearly all projections of catastrophic global warming, ocean heat uptake, and thermal-expansion-driven sea level rise are rooted in the presupposition that dramatic increases in radiative forcing from rising CO2 emissions will lead to pronounced increases in the EEI, scientists are now indicating we may not sufficiently understand these processes and thus we need to consider further study.
“Because the global energy budget before and after 1980 implies very different global warming in the future, further studies are required to better understand the cause of this historical variation.”
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