Editing IPCC:AR6/Data/Glossary (section)

== O ==

<div class="glossary-entry">
<div id="Ocean"></div>
=== <span class="glossary-term">Ocean</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII</div>

<div class="glossary-definition">'''Definition:''' The interconnected body of saline water that covers 71% of the Earth’s surface, contains 97% of the Earth’s water and provides 99% of the Earth’s biologically habitable space. It includes the Arctic, Atlantic, Indian, Pacific and Southern Oceans, as well as their marginal seas and coastal waters.</div>
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<div class="glossary-entry">
<div id="Ocean_acidification"></div>
=== <span class="glossary-term">Ocean acidification</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII</div>

<div class="glossary-longer-term">'''Full term:''' Ocean acidification (OA)</div>

<div class="glossary-definition">'''Definition:''' A reduction in the pH of the ocean, accompanied by other chemical changes (primarily in the levels of carbonate and bicarbonate ions), over an extended period, typically decades or longer, which is caused primarily by uptake of carbon dioxide (CO2) from the atmosphere, but can also be caused by other chemical additions or subtractions from the ocean. Anthropogenic OA refers to the component of pH reduction that is caused by human activity (IPCC, 2011, p. 37).</div>
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<div class="glossary-entry">
<div id="Ocean_alkalinization_Ocean_alkalinity_enhancement"></div>
=== <span class="glossary-term">Ocean alkalinization/Ocean alkalinity enhancement</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGIII</div>

<div class="glossary-definition">'''Definition:''' A proposed carbon dioxide removal (CDR) method that involves deposition of alkaline minerals or their dissociation products at the ocean surface. This increases surface total alkalinity, and may thus increase ocean 2) carbon dioxide (CO uptake and ameliorate surface ocean acidification.</div>
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<div class="glossary-entry">
<div id="Ocean_carbon_cycle"></div>
=== <span class="glossary-term">Ocean carbon cycle</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' The ocean carbon cycle is the set of processes that exchange carbon between various pools within the ocean, as well as between the atmosphere, Earth’s interior, cryosphere, and the sea-floor.</div>
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<div class="glossary-entry">
<div id="Ocean_deoxygenation"></div>
=== <span class="glossary-term">Ocean deoxygenation</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII</div>

<div class="glossary-definition">'''Definition:''' The loss of oxygen in the ocean. It results from ocean warming, which reduces oxygen solubility and increases oxygen consumption and stratification, thereby reducing the mixing of oxygen into the ocean interior. Deoxygenation can also be exacerbated by the addition of excess nutrients in the coastal zone.</div>
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<div class="glossary-entry">
<div id="Ocean_dynamic_sea_level_change"></div>
=== <span class="glossary-term">Ocean dynamic sea level change</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' Change in mean sea level relative to the geoid associated with circulation and density-driven changes in the ocean. Ocean dynamic sea level change is regionally varying but by definition has a zero global mean and conventionally is inverse-barometer corrected (i.e., the effect of the hydrostatic depression of the sea surface by atmospheric pressure changes is removed). Changes in ocean currents occur due to variations in heating and cooling, variability in winds and changes in seasonally to annually averaged air temperature and humidity.</div>
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<div class="glossary-entry">
<div id="Ocean_fertilisation"></div>
=== <span class="glossary-term">Ocean fertilisation</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGIII</div>

<div class="glossary-definition">'''Definition:''' A proposed carbon dioxide removal (CDR) method that relies on the deliberate increase of nutrient supply to the near-surface ocean with the aim of sequestering additional CO2 from the atmosphere through biological production. Methods include direct addition of micro-nutrients or macro-nutrients. To be successful, the additional carbon needs to reach the deep ocean where it has the potential to be sequestered on climatically relevant time scales.</div>
</div>

<div class="glossary-entry">
<div id="Ocean_heat_uptake_efficiency"></div>
=== <span class="glossary-term">Ocean heat uptake efficiency</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' This is a measure (W m –2 °C –1) of the rate at which heat storage by the global ocean increases as global surface temperature rises. It is a useful parameter for climate change simulations in which the radiative forcing is changing monotonically, when it can be compared with the c limate feedback parameter to gauge the relative importance of radiative response and ocean heat uptake in determining the rate of climate change. It can be estimated from such an experiment as the ratio of the rate of increase of ocean heat content to the surface temperature change.</div>
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<div class="glossary-entry">
<div id="Ocean_stratification"></div>
=== <span class="glossary-term">Ocean stratification</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII</div>

<div class="glossary-definition">'''Definition:''' Process of forming of layers of ocean water with different properties such as salinity, density and temperature that act as barriers to water mixing. The strengthening of near-surface stratification generally results in warmer surface waters, decreased oxygen levels in deeper water and intensification of ocean acidification (OA) in the upper ocean.</div>
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<div class="glossary-entry">
<div id="Offset"></div>
=== <span class="glossary-term">Offset</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGIII</div>

<div class="glossary-longer-term">'''Full term:''' Offset (in climate policy)</div>

<div class="glossary-definition">'''Definition:''' The reduction, avoidance or removal of a unit of greenhouse gas (GHG) emissions by one entity, purchased by another entity to counterbalance a unit of GHG emissions by that other entity. Offsets are commonly subject to rules and environmental integrity criteria intended to ensure that offsets achieve their stated mitigation outcome. Relevant criteria include, but are not limited to, the avoidance of double counting and leakage, use of appropriate baselines, additionality, and permanence or measures to address impermanence.</div>
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<div class="glossary-entry">
<div id="Orbital_forcing"></div>
=== <span class="glossary-term">Orbital forcing</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' Orbital forcing is the influence of slow, systematic and predictable changes in orbital parameters (eccentricity, obliquity and precession of the equinox) on incoming solar radiation (insolation), especially its latitudinal and seasonal distribution. It is an external forcing and a key driver of glacial–interglacial cycles.</div>
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<div class="glossary-entry">
<div id="Organic_aerosol"></div>
=== <span class="glossary-term">Organic aerosol</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' Component of the aerosol that consists of organic compounds, mainly carbon, hydrogen, oxygen and lesser amounts of other elements.</div>
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<div class="glossary-entry">
<div id="Organic_farming"></div>
=== <span class="glossary-term">Organic farming</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGIII</div>

<div class="glossary-definition">'''Definition:''' An agricultural production system that aims to utilise natural processes and cycles to limit off-farm and notably synthetic inputs, while also aiming to enhance agroecosystems and society. Organic farming is often legally defined and governed by standards, typically guided by principles outlined by the International Federation of Organic Agriculture Movements (IFOAM – Organics International) (IFOAM – Organics International, 2014).</div>
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<div class="glossary-entry">
<div id="Outbreak"></div>
=== <span class="glossary-term">Outbreak</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGII</div>

<div class="glossary-definition">'''Definition:''' Often used synonymously with ‘epidemic’, usually to indicate localised as opposed to generalised epidemics (WHO, 2020).</div>
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<div class="glossary-entry">
<div id="Outgoing_longwave_radiation"></div>
=== <span class="glossary-term">Outgoing longwave radiation</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' Net outgoing radiation in the infrared part of the spectrum at the top of the atmosphere.</div>
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<div class="glossary-entry">
<div id="Outlet_glacier"></div>
=== <span class="glossary-term">Outlet glacier</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' A glacier, usually between rock walls, that is part of, and drains, an ice sheet.</div>
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<div class="glossary-entry">
<div id="Overshoot_pathways"></div>
=== <span class="glossary-term">Overshoot pathways</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGIII</div>

<div class="glossary-definition">'''Definition:''' Pathways that first exceed a specified concentration, forcing, or global warming level, and then return to or below that level again before the end of a specified period of time (e.g., before 2100). Sometimes the magnitude and likelihood of the overshoot are also characterised. The overshoot duration can vary from one pathway to the next, but in most overshoot pathways in the literature and referred to as overshoot pathways in the AR6, the overshoot occurs over a period of at least one decade and up to several decades.</div>
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<div class="glossary-entry">
<div id="Oxygen_minimum_zone"></div>
=== <span class="glossary-term">Oxygen minimum zone</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII</div>

<div class="glossary-longer-term">'''Full term:''' Oxygen minimum zone (OMZ)</div>

<div class="glossary-definition">'''Definition:''' The midwater layer (200–1000 m) in the open ocean in which oxygen saturation is the lowest in the ocean. The degree of oxygen depletion depends on the largely bacterial consumption of organic matter, and the distribution of the OMZs is influenced by large-scale ocean circulation. In coastal oceans, OMZs extend to the shelves and may also affect benthic ecosystems.</div>
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<div class="glossary-entry">
<div id="Ozone"></div>
=== <span class="glossary-term">Ozone</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII; WGIII</div>

<div class="glossary-longer-term">'''Full term:''' Ozone (O3)</div>

<div class="glossary-definition">'''Definition:''' The triatomic form of oxygen, and a gaseous atmospheric constituent. In the troposphere, O 3 is created both naturally and by photochemical reactions involving gases resulting from human activities (e.g., smog). Tropospheric O 3 acts as a greenhouse gas (GHG). In the stratosphere, O 3 is created by the interaction between solar ultraviolet radiation and molecular oxygen (O 2). Stratospheric O 3 plays a dominant role in the stratospheric radiative balance. Its concentration is highest in the ozone layer.</div>
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<div class="glossary-entry">
<div id="Ozone-depleting_substances"></div>
=== <span class="glossary-term">Ozone-depleting substances</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-longer-term">'''Full term:''' Ozone-depleting substances (ODSs)</div>

<div class="glossary-definition">'''Definition:''' Man-made gases that destroy 3) ozone (O once they reach the ozone layer in the stratosphere. Ozone-depleting substances include: chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrobromofluorocarbons (HBFCs), halons, methyl bromide, carbon tetrachloride and methyl chloroform. They are used as refrigerants in commercial, home and vehicle air conditioners and refrigerators, foam blowing agents, components in electrical equipment, industrial solvents, solvents for cleaning (including dry cleaning), aerosol spray propellants and fumigants.</div>
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<div class="glossary-entry">
<div id="Ozone_layer"></div>
=== <span class="glossary-term">Ozone layer</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' A layer of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet radiation. It contains high concentrations of 3) ozone (O in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 to 35 kilometres (9.3 to 21.7 miles) above Earth, although its thickness varies seasonally and geographically.</div>
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<div class="glossary-entry">
<div id="Ozonesonde"></div>
=== <span class="glossary-term">Ozonesonde</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' An ozonesonde is a radiosonde measuring 3) ozone (O concentrations. The radiosonde is usually carried on a weather balloon and transmits measured quantities by radio to a ground-based receiver.</div>
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<div class="glossary-letter-section">