Stratospheric cooling and accountable carbon dioxide removal

Abstract

The vertical temperature structure of the atmosphere provides a clear physical fingerprint of anthropogenic greenhouse-gas forcing: the troposphere is warming while the stratosphere is cooling. Recent satellite-based fingerprinting shows that the mid-to-upper stratosphere, approximately 25–50 km above Earth, cooled by about 1–2 °C from 1986 to 2022. This Short Communication uses this vertical fingerprint as an atmospheric entry point to the broader Earth-system challenge of accountable carbon storage. Sedimentary, paleoclimatic and biogeochemical records show that carbon reservoirs differ fundamentally in capacity, persistence, reversibility and feedback across timescales from years to millennia and beyond. These constraints motivate a conceptual atmosphere-to-reservoir framework for comparing carbon dioxide removal (CDR) pathways through five common accounting questions: the counterfactual, additional atmospheric CO₂ removal, full-chain emissions and leakage or displacement, storage location and persistence over a stated accounting horizon, and measurement variability and Earth-system feedbacks. Applied consistently, the framework distinguishes gross carbon transfer or measured stock change from verifiable net atmospheric removal across land-based, ocean-based and engineered CDR pathways. Stratospheric cooling is therefore not a project-level CDR metric, but a physical reminder that accountable CDR ultimately requires demonstrable atmospheric CO₂ removal and sufficiently durable storage.