Barry, ChristianCullity, Garrett2025-05-232025-05-231470-594XWOS:001404108900001ORCID:/0000-0003-4847-4304/work/187930026ORCID:/0000-0002-2800-7904/work/187932881http://www.scopus.com/inward/record.url?scp=85216125535&partnerID=8YFLogxKhttps://hdl.handle.net/1885/733751914States and other climate actors now commonly set ‘net zero’ targets – pledging that, by a certain date, they will put no more carbon into the atmosphere than they take out. However, there is controversy over what exactly should count as attaining such targets. The method of emissions accounting that states currently use – territorial emissions accounting – is often criticized as problematic, but a fully satisfactory explanation of the problem is needed. We argue that the key both to understanding the problem and to solving it is that there is a specific kind of cooperative contribution – a mereological contribution – that a national net zero commitment needs to make to global climate action in order to meet the standards that global citizens should hold states to. On this basis, we propose an alternative method – Contributory Value-Chain Accounting – showing how it can be qualified to reflect trade relationships between net-zero-aligned countries, and defending it against the objections that it involves double counting, is infeasible and too informationally demanding, and that it would send the wrong incentive signals.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors gratefully acknowledge the financial support from the Australian Research Council (grant number DP 230101335) and visiting fellowships at the Institute for Futures Studies, Stockholm, the Global Priorities Institute at the University of Oxford, and the Population Well-Being Initiative at the University of Texas at Austin.28enPublisher Copyright: © The Author(s) 2025.carbon leakageclimate ethicscollective actionemissions accountingethics of cooperating groupsgreenhouse gas emissionsnationally determined contributionsnet zero202510.1177/1470594X24131242585216125535