Climate Alarmists Want To Reinstate The RCP8.5 Model
Yesterday’s New York Times featured an op-ed by David Wallace-Wells and Zeke Hausfather — a journalist and a climate ‘scientist’, respectively — both well known for their commitment to climate advocacy
Normally, yet another apocalyptic op-ed would not be worth commenting on, as they are a dime a dozen.
However, yesterday’s op-ed shows how the new CMIP7 climate models — discussed in detail here at THB — can smuggle the implausibly extreme, retired RCP8.5 back into climate science and policy discussions.
According to Hausfather, an IPCC AR7 lead author, the IPCC AR7 will adopt this strategy as well.
Misuse of RCP8.5 started early and snowballed from there, because no one corrected correctable missteps early on. We should not fall for this again.
The op-ed starts well enough, asserting accurately:
[P]rojected future warming has fallen quite a bit, and a worst-case emissions scenario known as “RCP8.5” — in which coal use would roughly quintuple by 2100 — is being phased out as implausible.
The op-ed then takes a sharp turn. Wallace-Wells and Hausfather claim:
[A] new round of forecasts from the climate science community is pretty alarming.
There are no new “forecasts” from the “climate science community.” The IPCC has always carefully explained that it does not forecast the future — appropriately so. It produces projections conditional on scenarios.
Further, results of Earth System model research with such conditional projections incorporating the new scenarios are still a ways off. An assessment of the “climate science community” will have to await the IPCC AR7.
The “forecasts” cited in the op-ed to the “climate science community” are in fact produced for a blog post by Hausfather.1
Based on Hausfather’s “forecasts,” the authors warn ominously (emphasis added):
“[H]arrowing temperature increases remain unnervingly possible. It’s not just that by moving too slowly we’ve lost the opportunity to avoid disruptive climate change. The high-end warming sometimes described as a ‘worst-case scenario’ remains very much on the table, too.”
That last sentence is a not-so-subtle reference to the assumed climate outcomes that emerged from the retired RCP8.5.
How can RCP8.5 be “phased out” while its implications remain ”very much on the table”?
Below I show how RCP8.5 is being brought right back into the discussion of climate science and policy via a Trojan Horse that carries a misuse of scenario extensions.
Step 1: Move the goalposts
Wallace-Wells and Hausfather forecast an apocalyptic-sounding future, which they characterize with a 75 percent likelihood this century:
“At three degrees higher [Celsius temperature increase over 1850-1900], the world’s ice sheets would be committed to millenniums of retreat. The share of species on land facing a high risk of extinction could double.
“How likely is this future? According to conventional modeling of today’s policies and pathways, the odds are about even by 2100 — and three in four by 2150.“
However, the claim that “conventional modeling of today’s policies and pathways” extends to 2150 is simply false. The creators of the new CMIP7 scenarios extended them to 2500.
Still, they are explicit (and responsible) in disclosing that these extensions are not based on modeling of policies and pathways (emphases added):
“[T]he scenario extensions will consist of emission and concentration trajectories to 2500 AD that are decoupled from the outcomes of IAM [Integrated Assessment Model] simulations.
While IAMs are useful in generating the plausible evolution of greenhouse gas emissions in the shorter-term, beyond the end of this century the uncertainties that increasingly affect the socio-economic drivers of these trajectories end up limiting the usefulness of IAMs for scenario design.”
The scenario extensions were not created to produce plausible futures, much less “forecasts” of the future, but instead to “explore the long-term Earth System dynamics“. The exploratory use of the extensions is entirely appropriate from a scientific perspective.
However, such extensions are not created to represent plausible futures, and thus they provide no basis for forecasts or plausible projections of the future.
However, moving the goalposts to 2150 is necessary to revive RCP8.5.
Step 2: Use 2150 as the basis for alarming predictions
Having argued (incorrectly) that the “scientific community” has modeled policies and pathways to 2150, the op-ed next extends its forecasts to 2150, again based on Hausfather’s blog post:
“There is also a voluminous scientific literature about an even more hair-raising level of temperature rise — between four and five degrees Celsius of warming this century. This is the true climate doomsday stuff, with most effects growing exponentially worse and damages compounding, likely arriving faster than farms, cities, coastlines and ecosystems can properly adapt. Recent models tell us that current policies give us about a 25 percent shot at exceeding four degrees by 2150.”
The reference here is to the new CMIP7 MEDIUM scenario, which has an exploratory extension that adds about 1,300 gigatonnes of carbon dioxide emissions from 2100 to 2150.
In a companion blog post to the op-ed, Hausfather goes further:
There is also no guarantee that we will stay in a current policy world. While I hope that countries will strengthen climate action over time, as we’ve seen in the US its also possible to directly subsidize fossil fuels and put up barriers to clean energy deployment.
In a world of policy reversal and active support for fossil fuel burning (the CMIP7 “High” scenario), we could end up well above 3C by 2100, have a ~70 percent chance of >4C by 2150, and a 30 percent chance of over 5C.
The HIGH-2150 scenario does indeed result in outcomes eerily similar to RCP8.5.
The figure below shows why that is — HIGH-2150 has essentially identical cumulative CO2 emissions to RCP8.5 through 2100.
The figure below shows the emissions trajectory of the HIGH-2150 scenario — the IAM-modeled emissions to 2100 plus the specified extension from 2100 to 2150. Emissions increase steadily over the next 125 years and are still rising in 2150.
The CMIP7 scenario committee noted that some assumptions may not be feasible due to their “geophysical plausibility” (recall the Ritchie and Dowlatabadi 2017 critique of RCP8.5 — it holds here as well):
[So]me outlier scenarios challenge current estimates of geophysical feasibility
But CMIP7 also reminds us that the extensions are meant to be exploratory, not necessarily plausible.
See more here climatechangedispatch
Bold emphasis added
Header image: Wikipedia
About the author: Roger Pielke Jr. has been a professor at the University of Colorado since 2001. Previously, he was a staff scientist in the Environmental and Societal Impacts Group of the National Center for Atmospheric Research. He has degrees in mathematics, public policy, and political science, and is the author of numerous books.
Charles Higley
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They (most people) still do not understand the Lambert-Beers Law in which the effect dwindles as CO2 concentration increases and reaches a point where increases do nothing,, asymptotically). We are almost there now, in fact.
As you add drops of milk to clear water, a laser beam initially goes right through the water, but as the water becomes murky with milk addition, the opacity increases and eventually the beam cannot pass through the murky water. No matter how much more milk is added, it is still opaque to the laser beam.
However, as the region (upper tropical troposphere) of the atmosphere that is claimed to be warming Earth’s surface is about -17 deg C (and cooling a little, according to NASA) and the surface is about 15 deg C, any IR radiation sent downward by this region would be rejected as those energy levels (equivalent to -17 dec C) are already full.
The bottomline is that no gas at any concentration in the atmosphere can warm the surface. AGW is a huge joke and an entirely political scam to garner control of the world’s people through power and money.
We need more CO2, not less, as it is plant food and greening the planet.
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Australian Scientist
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I am an Australian physicist who first alerted the CSIRO to the now‑demonstrated fact that their public claims about carbon dioxide, methane and water vapour warming the global mean surface temperature have never been scientifically verified. This is important because it is only the surface temperature that is claimed to be affected. If these trace gases cannot warm the surface, then the issues commonly grouped under “climate change” cannot be shown to relate to climate at all.
There are well‑established natural explanations for observed variations in the global mean surface temperature — most plausibly changes in cosmic‑ray flux influencing cloud formation. My website, https://climate-change-theory.info, contains my published scientific papers, including my first peer‑reviewed paper from 2012.
Freedom of Information responses confirm that CSIRO has never attempted to verify the IPCC’s claim that water vapour, carbon dioxide and methane warm the surface. Their energy diagrams depict these trace gases — only about 0.3% of the atmosphere — radiating roughly twice as much energy to the surface as the Sun, and imply that radiation from colder atmospheric layers can heat the warmer surface. This contradicts fundamental physics: the tropospheric temperature gradient is formed by gravity, a fact known by physicists since the 1870s.
I am currently awaiting a decision from the Commonwealth Ombudsman regarding my submission that CSIRO has engaged in negligent misstatement. A key issue is a statement on the CSIRO website claiming that greenhouse gases are “trapping heat.” CSIRO states:
“The cumulative effect of these emissions is to trap increasing amounts of heat in the Earth’s atmosphere, known as radiative forcing.”
This directly contradicts both the IPCC and Raymond Pierrehumbert’s authoritative textbook Principles of Planetary Climate (2010). On page 188, radiative forcing is defined strictly as a change in net radiative flux at the tropopause, not as heat being trapped in the atmosphere.
The physical behaviour of greenhouse gases also contradicts the “heat‑trapping” metaphor. CO₂ molecules are warmed mainly through collisions with nitrogen, oxygen and argon. These bulk gases cannot radiate, so CO₂ and water vapour are the only means by which the troposphere cools to space. If greenhouse gases truly trapped heat:
the troposphere would warm at night rather than cool,
the retained heat would accumulate each night,
and each day would begin warmer than the last, indefinitely.
No atmospheric dataset shows this behaviour. The “heat‑trapping” claim is therefore scientifically inaccurate and inconsistent with radiative‑transfer physics.
Given the seriousness of this contradiction between CSIRO’s public statements and established climate physics, I ask that you consider raising this matter with the relevant Minister and request clarification from CSIRO.
https://climate-change-theory.info
https://ssrn.com/author=2627605
https://americanthinker.com/author/douglasjcotton
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Khari Griffin
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“Someone amazing could be waiting for you right now. 💕” ………………..> spoold.com/s/4HjhigIS
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