Responsibility for Environmental Critical Transitions: Attributing the Approach in Place of the Crossing

Environmental harm following a critical transition presents a responsibility problem that ordinary causal doctrine handles badly. Many parties contributed forcing over decades; the transition occurred at a threshold whose crossing no party's contribution was sufficient to produce and which each party's contribution was necessary to; the harm manifested later; and the crossing itself was ordinarily not observed at the time. This paper proposes a relocation of the causal question. The method is conceptual and doctrinal. Its scope is deliberately narrow: the general difficulties of apportionment in distributed generative systems are treated in separate work and are not re-argued here, and the paper confines itself to what is specific to environmental transitions. The central claim is that causation of the crossing is not apportionable while causation of the approach is, and that responsibility should therefore attach to a party's contribution to the approach and not to its contribution to the transition. The ground is structural: at a threshold each contribution is necessary and none is sufficient, which is the configuration in which shares are undefined, whereas cumulative forcing toward the threshold is additive and admits shares by construction. Relocating the question to the approach makes the tractable quantity the object of the doctrine, and the paper argues this is what the leading proportional-contribution litigation has in substance already done, in affirming a principle of proportional liability for contribution to a global forcing while failing on the facts of the particular exposure. Three further results are developed. The relocation converts responsibility into a quantity over rates, which connects it to the differential treatment developed earlier in this series and makes the relevant evidence the record of a party's forcing over time. It supplies a determinate join to the supervisory duties treated in a companion paper, since a breach of an epistemic duty is evidence of a kind courts already receive and does not require the attribution the conduct-keyed regime was adopted to avoid. And it locates the discovery and limitation difficulty precisely, since a crossing established years after it occurred, by estimates a companion paper shows to be biased toward reporting stability, gives defendants an honest ignorance defence that the epistemic duties are the appropriate answer to. The paper surveys attribution science, the doctrines of necessity and sufficiency, proportional and market-share liability, and the climate litigation record.