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Glossary of terms

This page provides a glossary of words, terms and acronyms used throughout the website. To find the required term, use the A-Z listing below or search using your browser's page search (usually CTRL+F, or Command+F on a Mac).




Adjustment in natural or human systems in response to actual or expected climatic stimuli or their effects, which moderates harm or exploits beneficial opportunities.

Adaptive Capacity

The ability of a system to adjust to climate change (including climate variability and extremes), to moderate potential damages, to take advantage of opportunities, or to cope with the consequences.



The baseline (or reference) is any datum against which change is measured. It might be a "current baseline", in which case it represents observable, present-day conditions. It might also be a "future baseline", which is a projected future set of conditions excluding the driving factor of interest. Alternative interpretations of the reference conditions can give rise to multiple baselines.


The variability among living organisms from terrestrial, marine and other ecosystems. Biodiversity includes variability at the genetic, species and ecosystem levels.


Carbon Cycle

The term used to describe the flow of carbon (in various forms, e.g., as carbon dioxide (CO2)) through the atmosphere, ocean, terrestrial and marine biosphere and lithosphere.

Carbon Dioxide Capture and Storage

A process in which a relatively pure stream of carbon dioxide (CO2) from industrial and energy-related sources is separated (captured), conditioned, compressed and transported to a storage location for long-term isolation from the atmosphere.


Climate in a narrow sense is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization. The relevant quantities are most often surface variables such as temperature, precipitation and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.

Climate Change

Refers to a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). Climate change may be due to natural processes or external forcing, or to persistent anthropogenic changes in the composition of the atmosphere or in land-use.

Climate Model

A numerical representation of the climate system based on the physical, chemical and biological properties of its components, their interactions and feedback processes and accounting for some of its known properties. Climate models are applied as a research tool to study and simulate the climate and for operational purposes, including monthly, seasonal and interannual climate predictions.

Climate Projection

A climate projection is the simulated response of the climate system to a scenario of future emission or concentration of greenhouse gases (GHGs) and aerosols, generally derived using climate models.



The process of reducing coarse spatial scale model output to a finer scale. For Ireland, downscaling of GCMs to regional scale has been achieved using two approaches: Statistical downscaling of the outputs of a GCM and Dynamic downscaling which fits outputs from GCM into a regional climate model (RCM).


A period of abnormally dry weather long enough to cause a serious hydrological imbalance.

Dynamical Downscaling

Dynamical downscaling fits outputs from GCMs into a Regional Climate Model (RCM). The RCM is similar to a GCM but its spatial extent is limited to a portion of the globe. As a result, RCM can be nested within a GCM and simulate the effects of climate change at sub-GCM grid squares. Importantly, RCMs can include highly resolved geographic information such as complex topography and coastlines. This allows for an improved climatic simulation for more limited spatial areas, (e.g. at a regional level), than would be provided for by GCMs.



An ecosystem is a functional unit consisting of living organisms, their non-living environment and the interactions within and between them. Ecosystem boundaries can change over time. Ecosystems are nested within other ecosystems and their scale can range from very small to the entire biosphere.

Ecosystem Services

Ecological processes or functions having monetary or non-monetary value to individuals or society at large. These are frequently classified as (1) supporting services such as productivity or biodiversity maintenance, (2) provisioning services such as food, fibre or fish, (3) regulating services such as climate regulation or carbon sequestration and (4) cultural services such as tourism or spiritual and aesthetic appreciation.

Emission Scenario

A plausible representation of the future development of emissions of substances that are potentially radiatively active (e.g., greenhouse gases (GHGs), aerosols) based on a coherent and internally consistent set of assumptions about driving forces (such as demographic and socio-economic development, technological change, energy and land use) and their key relationships. Concentration scenarios, derived from emission scenarios, are used as input to a climate model to compute climate projections.

Energy Security

The goal of a given country, or the global community as a whole, to maintain an adequate, stable and predictable energy supply. Measures encompass safeguarding the sufficiency of energy resources to meet national energy demand at competitive and stable prices and the resilience of the energy supply; enabling development and deployment of technologies; building sufficient infrastructure to generate, store and transmit energy supplies and ensuring enforceable contracts of delivery.


A set of simulations (each one an ensemble member) made by either adjusting parameters within plausible limits of the model, or starting the model from different initial conditions. While many parameters are constrained by observations, some are subject to considerable uncertainty. The best way to investigate uncertainty is to run an ensemble experiment in which each relevant parameter combination is investigated. This is known as perturbed physics ensemble.


Over-enrichment of water by nutrients such as nitrogen and phosphorus. It is one of the leading causes of water quality impairment. The two most acute symptoms of eutrophication are hypoxia (or oxygen depletion) and harmful algal blooms.


The presence of people; livelihoods; species or ecosystems; environmental functions, services, and resources; infrastructure; or economic, social, or cultural assets in places and settings that could be adversely affected.

Exposure Unit

Represents the system considered to be at risk, can be defined by geographical extent, location, and distribution of a variety of population of receptors at risk.

External Forcing

External forcing refers to a forcing agent outside the climate system causing a change in the climate system. Volcanic eruptions, solar variations and anthropogenic changes in the composition of the atmosphere and land-use change are external forcings.

Extreme Weather Event

An extreme weather event is an event that is rare at a particular place and time of year. Definitions of rare vary, but an extreme weather event would normally be as rare as or rarer than the 10th or 90th percentile of a probability density function estimated from observations.



The overflowing of the normal confines of a stream or other body of water, or the accumulation of water over areas not normally submerged. Floods include river (fluvial) floods, flash floods, urban floods, pluvial floods, sewer floods, coastal floods and glacial lake outburst floods.



Geoengineering refers to a broad set of methods and technologies that aim to deliberately alter the climate system in order to alleviate the impacts of climate change. Most, but not all, methods seek to either (1) reduce the amount of absorbed solar energy in the climate system (Solar Radiation Management) or (2) increase net carbon sinks from the atmosphere at a scale sufficiently large to alter climate (Carbon Dioxide Removal).

Global Circulation Model (GCM)

A General Circulation Model (GCM), commonly referred to as a global climate model, is a mathematical representation of the general circulation of the planet's atmosphere or oceans based on mathematic equations to represent physical processes. These equations are the basis for computer programs commonly used to simulate the Earth's atmosphere or oceans. GCMs are widely used in weather forecasting and climate modelling.

Global Warming

Global warming refers to the gradual increase, observed or projected, in global surface temperature, as one of the consequences of radiative forcing caused by anthropogenic emissions.



The potential occurrence of a natural or human-induced physical event or trend that may cause loss of life, injury, or other health impacts, as well as damage and loss to property, infrastructure, livelihoods, service provision, ecosystems and environmental resources.

Heat Wave

A period of abnormally and uncomfortably hot weather.

Hydrological Cycle

The cycle in which water evaporates from the oceans and the land surface, is carried over the Earth in atmospheric circulation as water vapour, condenses to form clouds, precipitates over ocean and land as rain or snow, which on land can be intercepted by trees and vegetation, provides runoff on the land surface, infiltrates into soils, recharges groundwater, discharges into streams and ultimately flows out into the oceans, from which it will eventually evaporate again. The various systems involved in the hydrological cycle are usually referred to as hydrological systems.



The effects of climate change on natural and human systems. Depending on the consideration of adaptation, one can distinguish between potential and residual impacts. Potential impacts are all impacts that may occur given a projected climate, without considering adaptation. Residual impacts are the impacts that would occur after adaptation.

Industrial Revolution

A period of rapid industrial growth with far-reaching social and economic consequences, beginning in Britain during the second half of the 18th century and spreading to Europe and later to other countries including the United States. The invention of the steam engine was an important trigger of this development. The industrial revolution marks the beginning of a strong increase in the use of fossil fuels and emission of, in particular, fossil carbon dioxide (CO2).

Integrated Coastal Zone Management (ICZM)

An integrated approach for sustainably managing coastal areas, taking into account all coastal habitats and uses.


A perturbed state of a dynamical system is defined as irreversible on a given timescale, if the recovery timescale from this state due to natural processes is substantially longer than the time it takes for the system to reach this perturbed state.


Kyoto Protocol

Internationally legally binding agreement adopted under the UN Framework Convention on Climate Change at Kyoto in 1997 and ratified in 2005. The agreement aims to reduce the emissions of greenhouse gases.


Land Use

Land use refers to the total of arrangements, activities and inputs undertaken in a certain land cover type (a set of human actions). The term land use is also used in the sense of the social and economic purposes for which land is managed (e.g., grazing, timber extraction and conservation). In urban settlements it is related to land uses within cities and their hinterlands. Urban land use has implications on city management, structure and form and thus on energy demand, greenhouse gas (GHG) emissions and mobility, among other aspects.

Low Regrets Policy

A policy that would generate net social and/or economic benefits under current climate and a range of future climate change scenarios.



Action or investment that increase vulnerability to the impacts of climate change rather than reducing them.


An anthropogenic intervention to reduce the anthropogenic forcing of the climate system; it includes strategies to reduce greenhouse gas sources and emissions and enhance greenhouse gas sinks.


Natural Climate Variability

Variations in climate due to natural processes either internal to the climate system or due to external factors.

Net Negative Emissions

A situation of net negative emissions is achieved when, as result of human activities, more greenhouse gases (GHGs) are sequestered or stored than are released into the atmosphere.


Ocean Acidification

Ocean acidification refers to a reduction in the pH of the ocean 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.


Proactive Planning

Thinking ahead and anticipating/planning for change or crisis.


A projection is 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 realized.


Reactive Planning

Reacting to change or crisis after the event.

Regional Climate Model (RCM)

A Regional Climate Model (RCM) is a climate model of higher resolution than a global climate model (GCM) and can be nested within a GCM to provide more detailed simulations for a particular location/area.

Representative Concentration Pathways (RCPs)

Scenarios that include time series of emissions and concentrations of the full suite of greenhouse gases (GHGs) and aerosols and chemically active gases, as well as land use/land cover (Moss et al., 2008). The word representative signifies that each RCP provides only one of many possible scenarios that would lead to the specific radiative forcing characteristics. RCPs usually refer to the portion of the concentration pathway extending up to 2100, for which Integrated Assessment Models produced corresponding emission scenarios.


The capacity of social, economic and environmental systems to cope with a hazardous event or trend or disturbance, responding or reorganizing in ways that maintain their essential function, identity and structure, while also maintaining the capacity for adaptation, learning and transformation.


The potential for adverse consequences where something of value is at stake and where the occurrence and degree of an outcome is uncertain. In the context of the assessment of climate impacts, the term risk is often used to refer to the potential for adverse consequences of a climate-related hazard, or of adaptation or mitigation responses to such a hazard, on lives, livelihoods, health and well-being, ecosystems and species, economic, social and cultural assets, services (including ecosystem services), and infrastructure. Risk results from the interaction of vulnerability (of the affected system), its exposure over time (to the hazard), as well as the (climate-related) hazard and the likelihood of its occurrence.

Risk Management

The plans, actions or policies to reduce the likelihood and/or consequences of risks or to respond to consequences.



A description of a plausible future state which is not associated with a prescribed likelihood.


The uptake (i.e., the addition of a substance of concern to a reservoir) of carbon containing substances, in particular carbon dioxide (CO2), in terrestrial or marine reservoirs.


Any process, activity or mechanism that removes a greenhouse gas (GHG), an aerosol or a precursor of a GHG or aerosol from the atmosphere.

Statistical Downscaling

The statistical downscaling approach converts GCM/global-scale outputs to regional scale conditions. This is achieved by calibrating past climate information from GCMs to past climate observations for a region. On this basis, a predictive model is developed which is trained to match, as closely as possible, climate observations and is then employed to assess how large-scale future climate changes might be manifest on a regional basis.

Storm Surge

The temporary increase, at a particular locality, in the height of the sea due to extreme meteorological conditions (low atmospheric pressure and/or strong winds). The storm surge is defined as being the excess above the level expected from the tidal variation alone at that time and place.


A dynamic process that guarantees the persistence of natural and human systems in an equitable manner.

Sustainable Development

Development that meets the needs of the present without compromising the ability of future generations to meet their own needs (WCED, 1987).


Thermal Expansion

In connection with sea level, this refers to the increase in volume (and decrease in density) that results from warming water. A warming of the ocean leads to an expansion of the ocean volume and hence an increase in sea level.

Time Scale

In the scope of Climate change adaptation, the time scale can be cathegorised as follow:

  • Short term: In the context of current planning timescales (e.g. 0-5 years);
  • Medium term: In the context of subsequent planning cycles (e.g. >5-15 years);
  • Long Term: In the context of strategic planning (>15 years).

Tipping Point

A level of change in system properties beyond which a system reorganizes, often abruptly, and does not return to the initial state even if the drivers of the change are abated. For the climate system, it refers to a critical threshold when global or regional climate changes from one stable state to another stable state. The tipping point event may be irreversible.



Uncertainty relates to a state of having limited knowledge which can result from a lack of information or over disagreement over what is known or even knowable. Uncertainty may arise from many sources, such as quantifiable errors in data, or uncertain projections of human behaviour. Uncertainty can be represented by quantitative measures or by qualitative statements.



The propensity or predisposition to be adversely affected. Vulnerability encompasses a variety of concepts and elements including sensitivity or susceptibility to harm and lack of capacity to cope and adapt.



Weather refers to the state of the atmosphere with regard to temperature, cloudiness, rainfall, wind, and other meteorological conditions.