Recent Hunga Tonga Developments Part 1 - The APARC Report
These are the organisations who have collaborated in order to publish a very long and detailed report on Hunga Tonga under the acronym APARC (Atmospheric Processes and their Role in Climate):
Charles Rotter has published a very good, critical article on this voluminous report at Wattsupwiththat, which is recommended reading for anyone interested in Hunga Tonga. He opens:
When the Hunga Tonga–Hunga Haʻapai volcano erupted in January 2022, it immediately posed a problem—not merely scientific, but institutional. The eruption was the most explosive in the satellite era, injected an unprecedented quantity of water vapor into the stratosphere, and did so with a chemical signature unlike the canonical climate-cooling eruptions of the late twentieth century. It was followed, inconveniently, by a pronounced surge in global surface temperatures. The timing alone guaranteed scrutiny. What mattered was how that scrutiny would be framed.
As it happens, and as I have exhaustively documented since August 2023, that scrutiny was framed in terms of minimising or outright dismissing any possible connection between the eruption and the extraordinary jump in global mean surface temperature which began in June 2023 and started in the oceans in spring of 2023. Blaming the sudden increase on El Nino (which was only just beginning to develop in June 2023) was the preferred establishment option; climate scientists were extraordinarily reluctant to admit that there might be a new kid on the block as regards interannual global warming. The new APARC report, which reads more like an IPCC science based assessment report with its numerous chapters and long list of lead and supporting authors, represents what the establishment I am sure hope will be the ‘final word’ on Hunga Tonga - and those final words are:
The record-high global surface temperatures in 2023/2024 were not due to the Hunga eruption.
This singular statement should be final blow to all Hunga Tonga believing climate change deniers like myself who have argued for a significant role for Hunga Tonga in the 2023/24 warming. Not so, says the climate establishment, in an ‘authoritative 382 page report; volcanoes cool the planet, they do not warm the planet (unless there are lots of volcanoes and they are chucking out loads of CO2 and causing the Paleocene-Eocene Thermal Maximum, which the current anthropogenic release of CO2 is entirely analogous to, of course - but that’s another story). Charles Rotter says:
The resulting assessment report is vast, meticulous, and technically competent. It documents the eruption and its atmospheric aftermath in extraordinary detail, particularly in its observational chapters. Satellite measurements are cross-validated, transport pathways mapped, and instrumental uncertainties repeatedly acknowledged. The early sections read as careful empirical science, and much of the observational synthesis is genuinely valuable.
But the report is not merely descriptive. From its opening highlights onward, it signals a specific destination.
“The record-high global surface temperatures in 2023/2024 were not due to the Hunga eruption.”
That sentence appears in the Highlights section, not buried in the discussion, and not framed as provisional. It is one of the few categorical statements in the entire summary. Its placement matters. In a scientific inquiry, conclusions typically emerge from analysis. In this document, the conclusion precedes it.
The report then devotes hundreds of pages to ensuring that this statement remains unthreatened.
Quite. The intention of the report, I suggest, was not to investigate, genuinely and with an open mind, the possibility that Hunga Tonga may have caused the 2023/24 “global boiling” episode, it was to quash once and for all any mention that it might have, thus consigning such speculation to the realms of ‘settled science’ denial. The tactic is very familiar. After APARC, if you’re claiming that Hunga Tonga caused the 2023/24 warming spike, you are a climate change denying conspiracy theorist suffering from an incurable case of Dunning-Kruger syndrome. Rotter again:
The length of the report is not incidental. A short paper declaring Hunga irrelevant would have invited skepticism. Only a document of this scale—dense with data, models, intercomparisons, and caveats—could plausibly declare the case closed without appearing dismissive. The volume itself functions rhetorically, conveying finality through exhaustion.
None of this requires accusing the authors of misconduct. The report is careful, internally consistent, and often admirably cautious. But caution is not evenly distributed. Skepticism is applied asymmetrically. One explanation is forced to clear a high evidentiary bar; others pass unchallenged.
In that sense, the document reads less like an open scientific inquiry and more like a legal brief. Evidence is marshalled, counterarguments anticipated, uncertainties catalogued, and a verdict delivered early, then defended at length. The goal is not discovery, but closure.
Most revealing is this statement:
“This report has aligned closely with… upcoming international assessments.”
I’m guessing that chief amongst those “upcoming international assessments” is the upcoming UN IPCC AR7 WG1 report. So my note that the APARC report closely resembles an IPCC report is not merely a passing observation; it looks like APARC was constructed by the same people, using the same methodological framework, such that it would align closely with the forthcoming AR7 which we may expect will finally unruffle the hitherto distinctly ruffled feathers of the climate industrial complex caused by the extraordinary geological/atmospheric events of January 2022 and the subsequent “global boiling” of 2023/24.
The science which forms the basis of APARC’s dismissal of Hunga Tonga as the cause of 2023/24 warming is surprisingly meagre, consisting essentially of just a couple of scientific papers written by Schoeberl, Dessler et al, summing up the estimated stratospheric radiative impacts of water vapour and aerosols released by Hunga Tonga and their expected impact upon surface temperatures. It is no coincidence that one of the two lead authors of Chapter 7 of the APARC report, which details the radiative impacts of Hunga Tonga aerosols and water vapour, is Mark Schoeberl who, along with Dessler and others, published the original study which concluded that Hunga Tonga did not have any significant impact upon surface temperatures in the southern hemisphere in 2022. They followed up that initial analysis with this paper published in 2024. Aside from completely neglecting mention of any contribution to surface temperatures which may have arisen due to changes in circulation caused by Hunga Tonga, the possibility remains that Schoeberl and Dessler underestimated the direct radiative water vapour forcing and/or overestimated the effects of aerosol forcing. More on that in the follow up to this post.
It’s been annoying but it doesn’t really matter that the establishment has dissembled and censored on Hunga Tonga from day one. Its unprecedented effects are slowly but surely dissipating as shown by the UAH global tropospheric temperature series: https://www.drroyspencer.com/wp-content/uploads/UAH_LT_1979_thru_December_2025_v6.1_20x9-scaled.jpg.
I look forward to the day, in maybe a few months, when they have to confront the inconvenient fact that global temperatures are back to where they were almost 30 years ago.
The climate change hoax is imploding in the face of unavoidable reality, with the helpful assistance of President Trump who has just withdrawn from the UN IPCC and the UN FCCC.
regarding "the possibility is very real that Schoeberl and Dessler underestimated the direct radiative water vapour forcing and/or overestimated the effects of aerosol forcing."
Yes indeed! he possibility is very real—and not trivial—that Schoeberl, Dessler, and related 2024–2025 studies (including the APARC/WCRP assessment) underestimated the direct radiative forcing from the ~10% stratospheric water vapor increase and/or overestimated the compensating cooling from the co-injected aerosols.
Key reasons this remains plausible:Aerosol microphysics in models is acknowledged as challenging (e.g., the APARC report itself notes divergences in simulated growth rates, sedimentation, and decay), introducing substantial uncertainty in the negative forcing estimate (~-0.4 to -0.8 W/m² from aerosols).
Water vapor forcing calculations lean on the same core physics as older papers (Forster & Shine, Solomon et al.), which consistently yield positive ~0.2–0.4 W/m² for equivalent perturbations—yet recent works apply reductions or offsets without equivalent sensitivity testing for vapor dominance scenarios.
The eruption's plume was unusually high and water-rich with relatively low sulfur (compared to Pinatubo-class events), so extrapolating aerosol cooling efficacy from canonical volcanic cases may overestimate reflection.
The 10percent increase from Hunga Tunga may be underestimated, with some indications of a 15% global increase for a time.
Observational separation of signals remains difficult amid high interannual variability (El Niño, albedo shifts), allowing room for the net forcing to swing toward mild-to-moderate warming if aerosol effects decay faster or vapor persistence/latitude distribution amplifies greenhouse trapping more than modeled.
Critics (like myself, ha) argue this uncertainty was not symmetrically explored, with the burden placed heavily on proving vapor-driven warming rather than disproving it. Thus, a net positive forcing contribution to the 2023–2024 spike—potentially rivaling or exceeding El Niño/albedo factors—remains a legitimate alternative hypothesis within the bounds of established radiative physics.