An impact or airburst event initiated the freshwater or atmospheric perturbation that triggered the Atlantic circulation disruption behind the Younger Dryas cooling.

Physically conceivable, evidentially idle: known deglacial processes suffice for the AMOC disruption, no causal chain from a cosmic event to the ocean has been demonstrated, and a 2026 volcanic-forcing study now offers a rival trigger with source-discriminating geochemistry.

The claim that an impact initiated the AMOC disruption is weakly supported. The ocean circulation collapse is broadly accepted, but routing of glacial meltwater and sea-ice feedbacks provide robust, unassisted mechanisms for this disruption. The strongest opposing consideration is the recent identification of volcanic geochemical signatures at the boundary, which offers a competing and geochemically supported exotic trigger for the cooling, rendering the cosmic trigger physically conceivable but evidentially unnecessary.

It is physically conceivable that an impact or airburst could perturb freshwater routing, ice‑sheet stability, or atmospheric properties in a way that triggers the AMOC weakening behind the Younger Dryas (YDIH‑C013), and the proposed Taurid‑debris scenario offers a possible delivery mechanism (YDIH‑C012). However, there is no direct evidence that such an extraterrestrial perturbation occurred at the relevant time, and deglacial meltwater and sea‑ice feedbacks — now joined by a volcanic forcing candidate with its own geochemical support (YDIH‑E029) — already provide plausible triggers. The strongest opposing consideration is that the climate record itself does not show any distinctive signature that uniquely demands an impact‑initiated trigger over these terrestrial mechanisms.

Atlantic overturning weakening is well supported and can be initiated by meltwater routing, sea-ice feedbacks, and possibly volcanism without an impact; the 2026 Page-Ladson study offers a rival exotic trigger with actual source-discriminating geochemistry. No direct causal chain from a cosmic event to the ocean has been demonstrated in the evidence records. The strongest opposing consideration is that an impact-initiated ice-sheet destabilization remains physically conceivable and an unresolved trigger does not automatically privilege ordinary candidates. A trigger that known processes render unnecessary must still earn its place with positive evidence that has not survived scrutiny.

Physically conceivable but evidentially idle in this file: the AMOC weakening it must initiate is well supported (C013), and nothing in the climate record discriminates an impact initiator from meltwater routing, sea-ice feedbacks, or the 2026 volcanic-forcing candidate — which, unlike the impact trigger, arrived with source-discriminating geochemistry attached. The claim's truth therefore rides almost entirely on the boundary layer (C011), which is weak. Strongest opposing consideration: "known processes suffice" is itself a plausibility judgment — the AMOC initiation sequence is not resolved at decadal precision and the trigger slot is genuinely open — so an impact-initiated trigger is unevidenced rather than excludable, and this verdict leans partly on priors rather than on the provided records.

No evidence record demonstrates any causal chain from a cosmic event to the overturning circulation; the claim is physically conceivable but evidentially idle. Known deglacial processes plus, on the 2026 Page-Ladson result, a volcanic candidate with actual source-discriminating geochemistry behind it can initiate the circulation change without anything from the sky. The strongest opposing consideration is that the initiating trigger is genuinely unresolved, and "known processes suffice" is a plausibility judgment rather than a demonstration — an open question does not privilege the conventional candidates either. But an unnecessary trigger must supply positive evidence, and none survives.

Known deglacial processes suffice for the AMOC disruption (YDIH-E028), no causal chain from a cosmic event to the ocean has been demonstrated, and Page-Ladson (YDIH-E029) offers a rival volcanic trigger with actual source-discriminating geochemistry behind it.

AMOC weakening is well supported but its initiator is open, and known deglacial freshwater routing suffices (YDIH-E028); no causal chain from airburst to circulation disruption has been demonstrated. Page-Ladson (YDIH-E029) supplies a rival exotic trigger with source-discriminating geochemistry behind it, though it is a single very recent study.

AMOC weakening is well supported but its initiator is open, and known deglacial freshwater routing suffices (YDIH-E028); no causal chain from airburst to circulation change has been demonstrated. Page-Ladson (YDIH-E029) supplies a rival exotic trigger that at least carries source-discriminating geochemistry, though it is a single recent study needing replication.

AMOC weakening is well supported but its initiator is open, and known deglacial freshwater routing suffices (YDIH-E028); no causal chain from airburst to ocean circulation has been demonstrated. Page-Ladson (YDIH-E029) supplies a rival exotic trigger that at least carries source-discriminating geochemistry.

AMOC weakening is well supported but its initiator is open, and known deglacial freshwater routing suffices (YDIH-E028); no causal chain from airburst to circulation collapse has been demonstrated. Page-Ladson (YDIH-E029) supplies a rival exotic trigger that at least carries source-discriminating geochemistry, though it is itself a single recent study.

AMOC weakening is well supported but its initiator remains open, and known deglacial freshwater routing suffices (YDIH-E028); no causal chain from airburst to circulation disruption has been demonstrated. Page-Ladson (YDIH-E029) supplies a rival exotic trigger backed by source-discriminating geochemistry, though it is a single very recent study.

Physically conceivable but evidentially idle: known deglacial processes — meltwater routing, sea-ice feedbacks, and possibly volcanism, for which independent geochemical evidence appeared in 2026 — can produce the circulation change without an impact, and no direct causal chain from a cosmic event to the ocean has been demonstrated.

Ice-core chronologies synchronize the Younger Dryas cooling onset approximately 45 years prior to the GISP2 platinum spike, proving that whatever produced the platinum post-dated the initiation of cooling. Furthermore, competing geochemical evidence from ice cores and sediment profiles links the climate onset to a preceding cluster of major volcanic eruptions and conventional freshwater routing into the North Atlantic. The strongest opposing consideration is theoretical modeling suggesting that massive low-density cometary airbursts over the Laurentide Ice Sheet could hypothetically induce major freshwater discharges into ocean basins.

The case's best single observation cannot carry the trigger role: independent re-datings place the GISP2 platinum spike ~45 years after Greenland cooling began, with Green et al. 2025 concluding it "occurred too late to be a causal mechanism of the YDE." Meanwhile a cluster of four major bipolar eruptions sits correctly timed before the onset (Abbott 2021), and AMOC weakening has terrestrial candidate initiators. The strongest opposing consideration is that the lag is shown only for the platinum spike, not for a hypothetical undetected impactor signature, and the volcanic trigger is itself an unconfirmed candidate.

The Greenland platinum peak, the strongest accepted candidate event marker, is placed by YDIH-E038 and YDIH-E039 about 45 years after the cooling began and therefore cannot identify its initiator. YDIH-E029 supplies site-specific volcanic source evidence, while YDIH-E041 documents a substantial volcanic cluster before the onset, although neither proves volcanic causation. The broader proxy chronology does not independently establish a correctly timed impact or airburst. The strongest opposing consideration is that an unobserved pre-onset impact distinct from the platinum-producing event could still have initiated a perturbation, a possibility the supplied records do not test directly.

AMOC weakening is the accepted proximate cooling mechanism, but the best-attested candidate impact marker (GISP2 platinum) arrives ~45 years after onset on the shared chronology, and source-discriminating geochemistry at multiple sites favors volcanic rather than extraterrestrial forcing. Strongest opposing consideration is the theoretical possibility of an earlier, unmarked airburst, yet no supporting proxy or crater exists.

No record demonstrates an impact-initiated freshwater or atmospheric perturbation. Firestone et al. proposed one (E005) without measuring it, and the atmospheric route via soot and impact winter inherits the failure of the burning claim (C007). The GISP2 platinum sits about 45 years after the cooling began on the same GICC05 timescale (C507): if it is the event's fallout, the event came too late, and if it is not, the remaining sedimentary window (12,835–12,735 cal BP, E020) also lies at or beyond the young edge of the independently dated onset of ~12,870 ± 30 (E021), though comparing archives at decadal precision is genuinely hard. A correctly timed volcanic forcing is measured in the same ice (C508), Page-Ladson offers a volcanic rival with source evidence (E029), and the AMOC mechanism (C013) needs nothing from the sky. Strongest opposing consideration: the lag excludes the Greenland platinum as trigger fallout, not an impact that left no platinum in Greenland, and the volcanic rival is itself a timed forcing rather than a demonstrated cause (E041).

Physically conceivable but evidentially idle. Known deglacial processes can produce the circulation change without an impact, and no impact marker is tied to the onset: the Greenland platinum, once the best candidate, arrives about 45 years after the cooling began (YDIH-C507). A cluster of large eruptions, by contrast, does sit at the onset in both hemispheres' ice (YDIH-C508) — a correctly timed rival forcing, though not a demonstrated cause. Not contradicted: nothing shows an impact did not occur at the onset; the claim simply has nothing physical at the right moment.