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To achieve the Paris Agreement’s goal of limiting the increase in global average temperatures to “well below 2 degrees Celsius,” and ideally 1.5 degrees Celsius, above pre-industrial levels, global greenhouse gas (“GHG”) emissions must reach net zero in the second half of the century. The global community is not currently on track to achieve net zero emissions. In fact, with the exception of a slight dip during the Covid-19 pandemic, emissions have risen steadily in recent years. This, together with the increasingly visible impacts of climate change, has prompted growing interest in the possibility of removing GHGs directly from the atmosphere. While GHG removal cannot substitute for rapid and deep emissions cuts, it could help to offset residual emissions from hard-to-abate sectors and potentially even reduce the total atmospheric GHG load by delivering net negative emissions.

To date, efforts to advance GHG removal have primarily focused on developing carbon dioxide removal (“CDR”) techniques, but another GHG removal approach — atmospheric methane removal (“AMR”) — is now also beginning to receive attention. One AMR technique is atmospheric oxidation enhancement (“AOE”), which aims to accelerate the natural oxidation process whereby hydroxyl and chlorine radicals react with atmospheric methane, converting it into carbon dioxide and other by-products. This process could deliver significant climate benefits because methane is a particularly potent GHG, trapping 86 times more heat in the Earth’s atmosphere than carbon dioxide in the first 20 years after it is released and 34 times more heat than carbon dioxide over 100 years (on a ton-for-ton basis). However, AOE is still in the very early stages of development, and significantly more research is required to fully evaluate its efficacy and impacts (both positive and negative).

This paper, Atmospheric Oxidation Enhancement: The Legal Framework, and the two accompanying case studies, explore the international and domestic (U.S.) laws governing methane removal via AOE. Parts 1 and 2 introduce the concept of AOE, explain proposed AOE techniques, and discuss the climate and non-climate benefits and risks that AOE may present. Part 3 then discusses key factors that will influence how AOE projects are regulated, both at the international level and domestically in the United States. With respect to the latter, Part 3 examines circumstances under which the United States may assert jurisdiction over AOE projects and introduces the different bodies of U.S. law — arising at the federal, tribal, state, and local levels — that might apply to such projects. The remainder of the paper then assesses the laws and regulations that might govern AOE projects: Part 4 identifies international agreements and rules of customary international law that might affect whether, when, where, and how AOE projects are conducted, and Part 5 explores applicable U.S. law that might apply to such projects, with a particular focus on federal environmental law.

The paper is accompanied by two case studies that highlight permitting, reporting, and other legal requirements that could impact two hypothetical AOE projects: one involving the dispersal of AOE aerosol from onshore towers located in coastal areas, and another conducted by adding iron-bearing additives to marine fuels used in ocean-going vessels.


Environmental Chemistry | Environmental Law | International Law | Law | Water Law