O
- Occupational Safety and Health AdministrationUnited States federal regulatory agency
- Ocean acidification in the Great Barrier ReefThreat to the reef which harms corals
- Ocean Wind 1Cancelled wind energy project off New Jersey coast
- Oceana (conservation organization)Nonprofit ocean conservation organization
- Octabromodiphenyl etherChemical compound
- Odyssey (tanker)Oil tanker that sank in the North Atlantic
- Official Journal of the European UnionOfficial gazette of the European Union
- Offshore oil spill prevention and responseDisaster management study and practice
- Oil spillRelease of petroleum into the environment
- Oil–water separatorDevice to separate oil and water
- Ok Tedi MineCopper and gold mine in Papua New Guinea
- One-Dimensional Man1964 book by Herbert Marcuse
- Online youth radicalizationOnline youth radicalization is the action in which a young individual or a group of people
- Onsite sewage facilityWastewater systems to treat effluent on the same property that produces the wastewater
- Open defecationHumans defecating outside rather than into a toilet
- Open space reserveConserved land or water
- OpenAustralia FoundationThe OpenAustralia Foundation (OAF) is a non-profit organisation aimed at improving governm
- Operation Buster–JangleSeries of 1950s US nuclear tests
- Operation JulinOperation Julin was a group of 7 nuclear tests conducted by the United States in 1991–1992
- Operation National SwordThe Operation National Sword (ONS) was a policy initiative launched in 2017 by the governm
- Operation Ranch Hand1962–1971 US herbicidal warfare operation in the Vietnam War
- Operation Sea-SpraySecret biological warfare test by the US military
- Operation Tumbler–SnapperSeries of 1950s US nuclear tests
- Oregon Department of Environmental QualityThe Oregon Department of Environmental Quality (DEQ) is the chief regulatory agency of the
- Oregon Environmental CouncilThe Oregon Environmental Council (OEC) is an environmental advocacy group based in Portlan
- Organic cottonCotton grown organically from non-GM plants
- Organic horticultureOrganic horticulture is the science and art of growing fruits, vegetables, flowers, or orn
- Organisation for the Prohibition of Chemical WeaponsIntergovernmental organisation
- Organisation Internationale des Constructeurs d'AutomobilesInternational trade association
- Other effective area-based conservation measuresSpecific areas designated to conserve biodiversity
- Ottawa River (Lake Erie)The Ottawa River, also known as Ottawa Creek, is a short river, approximately 20 miles (32
- Ottawa Treaty1997 anti-personnel landmine ban treaty
- OverconsumptionResource use exceeding carrying capacity
- OverproductionExcess of supply over demand of products being offered to an economic market
- Overshoot (population)Phenomenon in which populations temporarily exceed carrying capacity of environment
- OxamylChemical compound