Editing IPCC:AR6/Glossary (section)

== P ==

<div class="glossary-entry">
<div id="Pacific_Decadal_Oscillation"></div>
=== <span class="glossary-term">Pacific Decadal Oscillation</span> ===

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

<div class="glossary-longer-term">'''Full term:''' Pacific Decadal Oscillation (PDO)</div>

<div class="glossary-definition">'''Definition:''' The leading mode of variability obtained from decomposition in empirical orthogonal function of sea surface temperature over the North Pacific north of 20°N, and characterized by a strong decadal component. The positive phase of the PDO features a dipole of sea surface temperature anomalies in the North Pacific, with a cold lobe near the centre of the basin and extending westward along the Kuroshio, encircled by warmer conditions along the coast of North America and in the subtropics. A positive PDO is accompanied by an intensified Aleutian Low and an associated cyclonic circulation enhancement leading to teleconnections over the continents adjacent to the North Pacific. In the AR6 WGI report, the PDO is encapsulated within the definition and description of Pacific Decadal Variability (PDV). See also Section AIV.2.6 in Annex IV of the AR6 WGI report. From Wikipedia During a "warm", or "positive", phase, the west Pacific becomes cooler and part of the eastern ocean warms; during a "cool", or "negative", phase, the opposite pattern occurs.</div>
</div>

<div class="glossary-entry">
<div id="Pacific_Decadal_Variability"></div>
=== <span class="glossary-term">Pacific Decadal Variability</span> ===

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

<div class="glossary-longer-term">'''Full term:''' Pacific Decadal Variability (PDV)</div>

<div class="glossary-definition">'''Definition:''' Coupled decadal-to-inter-decadal variability of the atmospheric circulation and underlying ocean that is typically observed over the entire Pacific Basin beyond the El Niño–Southern Oscillation (ENSO) time scale. In the AR6 WGI report, PDV encapsulates the Pacific Decadal Oscillation (PDO), the South Pacific Decadal Oscillation (SPDO), tropical Pacific decadal variability (also called decadal ENSO), and the Inter-decadal Pacific Oscillation (IPO). Typically, the positive phase of the PDV is characterized by anomalously high sea surface temperatures in the central-eastern tropical Pacific that extend to the extratropical North and South Pacific along the American coasts, encircled to the west by cold sea surface anomalies in the mid-latitude North and South Pacific. The negative phase is accompanied by sea surface temperature anomalies of the opposite sign. Those sea surface temperature anomalies are linked to anomalies in atmospheric and oceanic circulation throughout the whole Pacific Basin. The PDV is associated with decadal modulations in the relative occurrence of El Niño and La Niña. See Section AIV.2.6 in Annex IV of the AR6 WGI report.</div>
</div>

<div class="glossary-entry">
<div id="Pacific-North_American_pattern"></div>
=== <span class="glossary-term">Pacific-North American pattern</span> ===

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

<div class="glossary-longer-term">'''Full term:''' Pacific-North American (PNA) pattern</div>

<div class="glossary-definition">'''Definition:''' An atmospheric large-scale wave pattern featuring a sequence of tropospheric high and low pressure anomalies stretching from the subtropical west Pacific to the east coast of North America.</div>
</div>

<div class="glossary-entry">
<div id="PalaeoceneEocene_Thermal_Maximum"></div>
=== <span class="glossary-term">Palaeocene–Eocene Thermal Maximum</span> ===

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

<div class="glossary-longer-term">'''Full term:''' Palaeocene–Eocene Thermal Maximum (PETM)</div>

<div class="glossary-definition">'''Definition:''' The PETM is a transient event that occurred between 55.9 and 55.7 million years ago. Continental positions at this time were somewhat different to present due to tectonic plate movements. Geological data indicate that the PETM was characterised by a warming (global mean surface temperature rose to about 4°C–7 °C warmer than the preceding mean state), and an increase in atmospheric CO2 (from about 900 to about 2000 ppmv). In addition, ocean pH and oxygen content decreased; many deep-sea species went extinct and tropical coral reefs diminished.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Climate during periods prior to the development of measuring instruments, including historic and geologic time, for which only proxy climate records are available.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' A worldwide outbreak of a disease in humans in numbers clearly in excess of normal (WHO, 2020).</div>
</div>

<div class="glossary-entry">
<div id="Pareto_optimum"></div>
=== <span class="glossary-term">Pareto optimum</span> ===

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

<div class="glossary-definition">'''Definition:''' A state in which no one’s welfare can be increased without reducing someone one’s welfare. Wikipedia</div>
</div>

<div class="glossary-entry">
<div id="Participatory_governance"></div>
=== <span class="glossary-term">Participatory governance</span> ===

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

<div class="glossary-definition">'''Definition:''' A governance system that enables direct public engagement in decision-making using a variety of techniques, for example, referenda, community deliberation, citizen juries or participatory budgeting. The approach can be applied in formal and informal institutional contexts from national to local, but is usually associated with devolved decision making (Fung and Wright, 2003; Sarmiento and Tilly, 2018).</div>
</div>

<div class="glossary-entry">
<div id="Particulate_matter"></div>
=== <span class="glossary-term">Particulate matter</span> ===

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

<div class="glossary-longer-term">'''Full term:''' Particulate matter (PM)</div>

<div class="glossary-definition">'''Definition:''' Atmospheric aerosols involved in air pollution issues. Of greatest concern for health are particles of aerodynamic diameter less than or equal to 10 micrometers, usually designated as PM 10 and particles of diameter less than or equal to 2.5 micrometers, usually designated as PM 2.5.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Area covered with grass or other plants used or suitable for grazing of livestock; grassland.</div>
</div>

<div class="glossary-entry">
<div id="Path_dependence"></div>
=== <span class="glossary-term">Path dependence</span> ===

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

<div class="glossary-definition">'''Definition:''' The generic situation where decisions, events, or outcomes at one point in time constrain adaptation, mitigation or other actions or options at a later point in time.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' The temporal evolution of natural and/or human systems towards a future state. Pathway concepts range from sets of quantitative and qualitative scenarios or narratives of potential futures to solution-oriented decision-making processes to achieve desirable societal goals. Pathway approaches typically focus on biophysical, techno-economic, and/or socio-behavioural trajectories and involve various dynamics, goals, and actors across different scales.</div>
</div>

<div class="glossary-entry">
<div id="Pattern_scaling"></div>
=== <span class="glossary-term">Pattern scaling</span> ===

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

<div class="glossary-definition">'''Definition:''' Techniques used to represent the spatial variations in climate at a given increase in global mean surface air temperature (GSAT) are referred to as ‘pattern scaling’.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Soft, porous or compressed, sedentary deposit of which a substantial portion is partly decomposed plant material with high water content in the natural state (up to about 90%).</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Peatlands are wetland ecosystems where soils are dominated by peat. In peatlands, net primary production exceeds organic matter decomposition as a result of waterlogged conditions, which leads to the accumulation of peat.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' The pelagic zone consists of the entire water column of the open ocean. It is subdivided into the epipelagic zone (<200 m, the uppermost part of the ocean that receives enough sunlight to allow photosynthesis), the mesopelagic zone (200–1000 m depth) and the bathypelagic zone (>1000 m depth). The term ‘pelagic’ can also refer to organisms that live in the pelagic zone.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Organisms large and small living in the pelagic zones. Includes plankton (small) and nekton (free swimming, large). See Benthos.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' A partition value in a population distribution that a given percentage of the data values are below or equal to. The 50th percentile corresponds to the median of the population. Percentiles are often used to estimate the extremes of a distribution. For example, the 90th (10th) percentile may be used to refer to the threshold for the upper (lower) extremes.</div>
</div>

<div class="glossary-entry">
<div id="Peri-urban_areas"></div>
=== <span class="glossary-term">Peri-urban areas</span> ===

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

<div class="glossary-definition">'''Definition:''' Dynamic transition zones that have intense interaction between rural and urban economies, activities, households, and lifestyles. Neither fully rural or urban (Seto et al., 2010).</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Ground (soil or rock, and included ice and organic material) that remains at or below 0°C for at least two consecutive years (Harris et al., 1988). Note that permafrost is defined via temperature rather than ice content and, in some instances, may be ice-free.</div>
</div>

<div class="glossary-entry">
<div id="Permafrost_degradation"></div>
=== <span class="glossary-term">Permafrost degradation</span> ===

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

<div class="glossary-definition">'''Definition:''' Decrease in the thickness and/or areal extent of permafrost.</div>
</div>

<div class="glossary-entry">
<div id="Permafrost_thaw"></div>
=== <span class="glossary-term">Permafrost thaw</span> ===

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

<div class="glossary-definition">'''Definition:''' Progressive loss of ground ice in permafrost, usually due to input of heat. Thaw can occur over decades to centuries over the entire depth of permafrost ground, with impacts occurring while thaw progresses. During thaw, temperature fluctuations are subdued because energy is transferred by phase change between ice and water. After the transition from permafrost to non-permafrost, ground can be described as thawed.</div>
</div>

<div class="glossary-entry">
<div id="Perturbed_parameter_ensemble"></div>
=== <span class="glossary-term">Perturbed parameter ensemble</span> ===

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

<div class="glossary-definition">'''Definition:''' Parameter ensembles in which model parameters are varied in a systematic manner, aim to assess the uncertainty resulting from internal model specifications within a single model.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' The relationship between biological phenomena that recur periodically (e.g., development stages, migration) especially related to climate and seasonal changes.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' The production of carbohydrates in plants, algae and some bacteria using the energy of light. Carbon dioxide (CO 2) is used as the carbon source.</div>
</div>

<div class="glossary-entry">
<div id="Physical_climate_storyline"></div>
=== <span class="glossary-term">Physical climate storyline</span> ===

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

<div class="glossary-definition">'''Definition:''' A self-consistent and plausible unfolding of a physical trajectory of the climate system, or a weather or climate event, on time scales from hours to multiple decades (Shepherd et al., 2018). Through this, storylines explore, illustrate and communicate uncertainties in the climate system response to forcing and in internal variability.</div>
</div>

<div class="glossary-entry">
<div id="Planetary_health"></div>
=== <span class="glossary-term">Planetary health</span> ===

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

<div class="glossary-definition">'''Definition:''' A concept based on the understanding that human health and human civilisation depend on ecosystem health and the wise stewardship of ecosystems.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Free-floating organisms living in the upper layers of aquatic systems. Their distribution and migration are primarily determined by water currents. A distinction is made between phytoplankton, which depend on photosynthesis for their energy supply, and zooplankton, which feed on phytoplankton, other zooplankton and bacterioplankton.</div>
</div>

<div class="glossary-entry">
<div id="Planned_relocation"></div>
=== <span class="glossary-term">Planned relocation</span> ===

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

<div class="glossary-longer-term">'''Full term:''' Planned relocation (of humans)</div>

<div class="glossary-definition">'''Definition:''' A form of human mobility response in the face of sea level rise and related impacts. Planned relocation is typically initiated, supervised and implemented from national to local level and involves small communities and individual assets but may also involve large populations. Also termed resettlement, managed retreat or managed realignment.</div>
</div>

<div class="glossary-entry">
<div id="Plant_evaporative_stress"></div>
=== <span class="glossary-term">Plant evaporative stress</span> ===

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

<div class="glossary-definition">'''Definition:''' Plant evaporative stress in both crops and natural vegetation can result from the combination of a high atmospheric evaporative demand and limited available water to supply this demand by means of evapotranspiration, further enhancing agricultural and ecological drought.</div>
</div>

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

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

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

<div class="glossary-definition">'''Definition:''' Change in organismal trait values in response to an environmental cue and which does not require change in underlying DNA sequence.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' The Pleistocene Epoch is the earlier of two epochs in the Quaternary System, extending from 2.59 Ma to the beginning of the Holocene at approximately 11.7 ka.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' The Pliocene Epoch is the more recent of two epochs of the Neogene Period within the Cenozoic Era. It extends from 5.33 Ma to the beginning of the Pleistocene Epoch at 2.59 Ma. The Neogene Period precedes the current geological period, the Quaternary Period, which is one of several ice ages that have occurred during Earth’s geological history. It encompasses the mid-Pliocene warm period (MPWP), also known as the Piacenzian warm period, which occurred from approximately 3.3 to 3.0 Ma. The MPWP, in turn, encompasses the interglacial episode, marine isotope stage (MIS) KM5c, which peaked at 3.205 Ma, when orbital forcing was similar to modern (Haywood et al., 2016).</div>
</div>

<div class="glossary-entry">
<div id="Polar_amplification"></div>
=== <span class="glossary-term">Polar amplification</span> ===

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

<div class="glossary-definition">'''Definition:''' Polar amplification describes the phenomenon where surface temperature change at high latitudes exceeds the global average surface temperature change. The terms Arctic amplification or Antarctic amplification are used when describing the phenomenon occurring at one of the poles.</div>
</div>

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

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

<div class="glossary-longer-term">'''Full term:''' Policies (for climate change mitigation and adaptation)</div>

<div class="glossary-definition">'''Definition:''' Strategies that enable actions to be undertaken to accelerate adaptation and mitigation. Policies include those developed by national and subnational public agencies, and with the private sector. Policies for adaptation and mitigation often take the form of economic incentives, regulatory instruments, and decision-making and engagement processes.</div>
</div>

<div class="glossary-entry">
<div id="Political_economy"></div>
=== <span class="glossary-term">Political economy</span> ===

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

<div class="glossary-definition">'''Definition:''' The set of interlinked relationships between people, the State, society and markets as defined by law, politics, economics, customs and power that determine the outcome of trade and transactions and the distribution of wealth in a country or economy.</div>
</div>

<div class="glossary-entry">
<div id="Pollen_analysis"></div>
=== <span class="glossary-term">Pollen analysis</span> ===

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

<div class="glossary-definition">'''Definition:''' A technique of both relative dating and environmental reconstruction, consisting of the identification and counting of pollen types preserved in peat, lake sediments and other deposits.</div>
</div>

<div class="glossary-entry">
<div id="Polycentric_governance"></div>
=== <span class="glossary-term">Polycentric governance</span> ===

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

<div class="glossary-definition">'''Definition:''' Polycentric governance involves multiple centres of decision-making with overlapping jurisdictions. While the centres have some degree of autonomy, they also take each other into account, coordinating their actions and seeking to resolve conflicts (Carlisle and Gruby, 2017; Jordan et al., 2018; McGinnis and Ostrom, 2012).</div>
</div>

<div class="glossary-entry">
<div id="Pool,_carbon_and_nitrogen"></div>
=== <span class="glossary-term">Pool, carbon and nitrogen</span> ===

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

<div class="glossary-definition">'''Definition:''' A reservoir in the Earth System where elements, such as carbon and nitrogen, reside in various chemical forms for a period of time.</div>
</div>

<div class="glossary-entry">
<div id="Potential_evapotranspiration"></div>
=== <span class="glossary-term">Potential evapotranspiration</span> ===

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

<div class="glossary-definition">'''Definition:''' The potential rate of water loss from wet soils and from plant surfaces, without any limits imposed by the water supply.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' A complex concept with several definitions stemming from different schools of thought. It can refer to material circumstances (such as need, pattern of deprivation or limited resources), economic conditions (such as standard of living, inequality or economic position) and/or social relationships (such as social class, dependency, exclusion, lack of basic security or lack of entitlement).</div>
</div>

<div class="glossary-entry">
<div id="Poverty_eradication"></div>
=== <span class="glossary-term">Poverty eradication</span> ===

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

<div class="glossary-definition">'''Definition:''' A set of measures to end poverty in all its forms everywhere.</div>
</div>

<div class="glossary-entry">
<div id="Poverty_trap"></div>
=== <span class="glossary-term">Poverty trap</span> ===

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

<div class="glossary-definition">'''Definition:''' Poverty trap is understood differently across disciplines. In the social sciences, the concept, primarily employed at the individual, household or community level, describes a situation in which escaping poverty becomes impossible due to unproductive or inflexible resources. A poverty trap can also be seen as a critical minimum asset threshold, below which families are unable to successfully educate their children, build up their productive assets and get out of poverty. Extreme poverty is itself a poverty trap since poor persons lack the means to participate meaningfully in society. In economics, the term poverty trap is often used at national scales, referring to a self-perpetuating condition where an economy, caught in a vicious cycle, suffers from persistent underdevelopment (Matsuyama, 2008). Many proposed models of poverty traps are found in the literature.</div>
</div>

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

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

<div class="glossary-longer-term">'''Full term:''' Pre-industrial (period)</div>

<div class="glossary-definition">'''Definition:''' The multi-century period prior to the onset of large-scale industrial activity around 1750. The reference period 1850–1900 is used to approximate pre-industrial global mean surface temperature (GMST).</div>
</div>

<div class="glossary-entry">
<div id="Precipitable_water"></div>
=== <span class="glossary-term">Precipitable water</span> ===

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

<div class="glossary-definition">'''Definition:''' The total amount of atmospheric water vapour in a vertical column of unit cross-sectional area. It is commonly expressed in terms of the height of the water if completely condensed and collected in a vessel of the same unit cross section.</div>
</div>

<div class="glossary-entry">
<div id="Precipitation_deficit"></div>
=== <span class="glossary-term">Precipitation deficit</span> ===

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

<div class="glossary-definition">'''Definition:''' A period with an abnormal precipitation deficit is defined as a meteorological drought.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' Atmospheric compounds that are not greenhouse gases (GHGs) or aerosols, but that have an effect on GHG or aerosol concentrations by taking part in physical or chemical processes regulating their production or destruction rates.</div>
</div>

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

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

<div class="glossary-definition">'''Definition:''' The extent to which future states of a system may be predicted based on knowledge of current and past states of the system. Because knowledge of the climate system’s past and current states is generally imperfect, as are the models that utilize this knowledge to produce a climate prediction, and because the climate system is inherently non-linear and chaotic, predictability of the climate system is inherently limited. Even with arbitrarily accurate models and observations, there may still be limits to the predictability of such a non-linear system (AMS, 2021).</div>
</div>

<div class="glossary-entry">
<div id="Prediction_quality_skill"></div>
=== <span class="glossary-term">Prediction quality/skill</span> ===

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

<div class="glossary-definition">'''Definition:''' Measures of the success of a prediction against observationally based information. No single measure can summarize all aspects of forecast quality, and a suite of metrics is considered. Metrics will differ for forecasts given in deterministic and probabilistic form.</div>
</div>

<div class="glossary-entry">
<div id="Primary_energy"></div>
=== <span class="glossary-term">Primary energy</span> ===

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

<div class="glossary-definition">'''Definition:''' The energy that is embodied in resources as they exist in nature (e.g., coal, biomass uranium, solar radiation, wind, ocean currents) (Grubler et al. 2012). [Note: Primary energy is defined in several alternative ways. The method used in this report is the direct equivalent method, which counts one unit of secondary energy provided from non-combustible sources as one unit of primary energy. For more details on the methodology, see Section 7 in Working Group III Annex II.]</div>
</div>

<div class="glossary-entry">
<div id="Primary_production"></div>
=== <span class="glossary-term">Primary production</span> ===

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

<div class="glossary-definition">'''Definition:''' The synthesis of organic compounds by plants and microbes, on land or in the ocean, primarily by photosynthesis using light and 2) carbon dioxide (CO as sources of energy and carbon, respectively. It can also occur through chemosynthesis, using chemical energy, for example, in deep sea vents.</div>
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<div class="glossary-entry">
<div id="Private_costs"></div>
=== <span class="glossary-term">Private costs</span> ===

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

<div class="glossary-definition">'''Definition:''' Costs carried by individuals, companies or other private entities that undertake an action, whereas social costs include additionally the external costs on the environment and on society as a whole. Quantitative estimates of both private and social costs may be incomplete, because of difficulties in measuring all relevant effects.</div>
</div>

<div class="glossary-entry">
<div id="Probability_density_function"></div>
=== <span class="glossary-term">Probability density function</span> ===

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

<div class="glossary-longer-term">'''Full term:''' Probability density function (PDF)</div>

<div class="glossary-definition">'''Definition:''' A probability density function is a function that indicates the relative chances of occurrence of different outcomes of a variable. The function integrates to unity over the domain for which it is defined and has the property that the integral over a sub-domain equals the probability that the outcome of the variable lies within that sub-domain. For example, the probability that a temperature anomaly defined in a particular way is greater than zero is obtained from its PDF by integrating the PDF over all possible temperature anomalies greater than zero. Probability density functions that describe two or more variables simultaneously are similarly defined.</div>
</div>

<div class="glossary-entry">
<div id="Procedural_justice"></div>
=== <span class="glossary-term">Procedural justice</span> ===

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

<div class="glossary-definition">'''Definition:''' Justice in the way outcomes are brought about including who participates and is heard in the processes of decision-making.</div>
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<div class="glossary-entry">
<div id="Process-based_model"></div>
=== <span class="glossary-term">Process-based model</span> ===

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

<div class="glossary-definition">'''Definition:''' Theoretical concepts and computational methods that represent and simulate the behaviour of real-world systems derived from a set of functional components and their interactions with each other and the system environment, through physical and mechanistic processes occurring over time.</div>
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<div class="glossary-entry">
<div id="Production-based_emissions"></div>
=== <span class="glossary-term">Production-based emissions</span> ===

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

<div class="glossary-definition">'''Definition:''' Emissions released to the atmosphere for the production of goods and services by a certain entity (e.g., a person, firm, country, or region).</div>
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<div class="glossary-entry">
<div id="Projection"></div>
=== <span class="glossary-term">Projection</span> ===

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

<div class="glossary-definition">'''Definition:''' A potential future evolution of a quantity or set of quantities, often computed with the aid of a model. Unlike predictions, projections are conditional on assumptions concerning, for example, future socio-economic and technological developments that may or may not be realised.</div>
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<div class="glossary-entry">
<div id="Prosumers"></div>
=== <span class="glossary-term">Prosumers</span> ===

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

<div class="glossary-definition">'''Definition:''' A consumer that also produces energy and inputs energy to the system, for which it is an active agent in the energy system and market.</div>
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<div class="glossary-entry">
<div id="Proxy"></div>
=== <span class="glossary-term">Proxy</span> ===

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

<div class="glossary-definition">'''Definition:''' A proxy climate indicator is any biophysical property of materials formed during the past that is interpreted to represent some combination of climate-related variations back in time. Climate-related data derived in this way are referred to as proxy data, and time series of proxy data are proxy records. Examples of proxy types include pollen assemblages, tree ring widths, speleothem and coral geochemistry, and various data derived from marine sediments and glacier ice. Proxy data can be calibrated to provide quantitative climate information.</div>
</div>

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<div class="glossary-letter-section">