Achieving net-zero CO₂ emissions globally requires an annual removal of on the order of 7–9 Gt CO₂; but current CO₂ removal (CDR) measurement methodologies are not designed to quantify marine CDR (mCDR) at the megaton-to-gigaton scales required for climate relevance. This perspective presents a new methodology, the Atmospheric CO₂ Perimeter Flux (ACPF) method, an atmospheric-domain framework for the monitoring, reporting, and verification (MRV) of marine carbon dioxide removal. ACPF relies on a network of autonomous surface vehicles (ASVs) that monitor CO₂ concentration and wind vector in the well-mixed marine boundary layer (MBL) above the mCDR region. The sensors integrate net CO₂ mass flux in the MBL across the perimeter in tonnes per hour. Paired upwind and downwind ASVs track the sampled air mass, suppressing synoptic-scale CO₂ variability common to both ends of the transect. The difference between upwind and downwind CO2 values can be converted into XCO₂ difference values comparable to satellite retrievals. The framework constrains net surface exchange over the enclosed region without ocean-interior observations or a biological-pump model. Attributing that exchange to an intervention requires a baseline obtained by the same array, over the same region. The magnitude of the signal that ACPF must resolve is assessed against the surface CO₂ depletion implied by the post-Pinatubo atmospheric anomaly. The ACPF architecture applies to any bounded mCDR intervention that generates a measurable surface CO₂ depletion at the megaton-to-gigaton-per-year scale required by today’s net-zero commitments.