C
Glossary and Acronyms


AAO

Antarctic Oscillation

Abrupt climate change

An abrupt climate change occurs when the climate system is forced to cross some threshold, triggering a transition to a new state at a rate determined by the climate system itself and faster than the cause. (NRC, 2002)

ACE 1 and 2

Aerosol Characterization Experiments

ACRIM

Active Cavity Radiometer Irradiance Monitor

Aerosol

A colloidal system in which the dispersed phase is composed of either solid or liquid particles and in which the dispersion medium is some gas, usually air. There is no clear-cut upper limit to the size of particles composing the dispersed phase in an aerosol, but as in all other colloidal systems, it is rather commonly set at 1 μm. Haze, most smokes, and some fogs and clouds may thus be regarded as aerosols. However, it is not good usage to apply the term to ordinary clouds with drops so large as to rule out the usual concept of colloidal stability. It is also poor usage to apply the term to the dispersed particles alone; an aerosol is a system of dispersed phase and dispersing medium taken together. (American Meteorological Society [AMS])

AIM

Asia-Pacific Integrated Model

Albedo

The ratio of reflected flux density to incident flux density, referenced to some surface. Albedos commonly tend to be broadband ratios, usually referring either to the entire spectrum of solar radiation or to just



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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties C Glossary and Acronyms AAO Antarctic Oscillation Abrupt climate change An abrupt climate change occurs when the climate system is forced to cross some threshold, triggering a transition to a new state at a rate determined by the climate system itself and faster than the cause. (NRC, 2002) ACE 1 and 2 Aerosol Characterization Experiments ACRIM Active Cavity Radiometer Irradiance Monitor Aerosol A colloidal system in which the dispersed phase is composed of either solid or liquid particles and in which the dispersion medium is some gas, usually air. There is no clear-cut upper limit to the size of particles composing the dispersed phase in an aerosol, but as in all other colloidal systems, it is rather commonly set at 1 μm. Haze, most smokes, and some fogs and clouds may thus be regarded as aerosols. However, it is not good usage to apply the term to ordinary clouds with drops so large as to rule out the usual concept of colloidal stability. It is also poor usage to apply the term to the dispersed particles alone; an aerosol is a system of dispersed phase and dispersing medium taken together. (American Meteorological Society [AMS]) AIM Asia-Pacific Integrated Model Albedo The ratio of reflected flux density to incident flux density, referenced to some surface. Albedos commonly tend to be broadband ratios, usually referring either to the entire spectrum of solar radiation or to just

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties the visible portion. More precise work requires the use of spectral albedos, referenced to specific wavelengths. Visible albedos of natural surfaces range from low values of 0.04 for calm, deep water and overhead Sun, to 0.8 for fresh snow or thick clouds. Many surfaces show an increase in albedo with increasing solar zenith angle. (AMS) ALE Atmospheric Lifetime Experiment AMIP Atmospheric Model Intercomparison Project Amphiphilic Of, relating to, or being a compound (as a surfactant) consisting of molecules having a polar, water-soluble group attached to a water-insoluble hydrocarbon chain; also: being a molecule of such a compound. AO Arctic Oscillation AOGCM Atmosphere-Ocean General Circulation Model ARGO A global array that will eventually include approximately 3000 free-drifting profiling floats that measure the temperature and salinity of the upper 2000 m of the ocean. ARM Atmospheric Radiation Measurement ASF Model Atmospheric Stabilization Framework Model A-Train A planned satellite formation consisting of two of the major EOS missions, three Earth System Science Pathfinder missions, and a French Centre National d’Etudes Spatiales (CNES) mission flying along the same orbit track and separated by only a few minutes. AVHRR Advanced Very High Resolution Radiometer Black carbon (BC) Light-absorbing carbonaceous aerosol, including elemental carbon and low-volatility organic compounds. BLAG (Berner/Lasaga/Garrels) hypothesis Variations in seafloor spreading rates lead to variations in volcanic outgassing and, thus, atmospheric CO2 concentrations. Bowen ratio The ratio of sensible to latent heat fluxes from the Earth’s surface up into the atmosphere. Typical values are 5 over semiarid regions, 0.5 over grasslands and forests, 0.2 over irrigated orchards or grass, 0.1 over the sea, and negative in some advective situations such as over oases where sensible heat flux can be downward while latent heat flux is upward. (AMS) BSRN Baseline Surface Radiation Network

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties CCN Cloud condensation nuclei CFC Chlorofluorocarbon Climate feedback An amplification or dampening of the climate response to a specific forcing due to changes in the atmosphere, oceans, land, or continental glaciers. Climate forcing An energy imbalance imposed on the climate system either externally or by human activities. Climate model A simplified mathematical representation of the Earth’s climate system. Climate response Change in the climate system resulting from a climate forcing. Climate sensitivity parameter or climate feedback parameter (λ) The equilibrium global mean temperature change (°C) for a 1 W m−2 TOA radiative forcing. λ is typically in the range of 0.3-1.4°C m2 W−1 in the current generation of GCMs. Climate sensitivity has played a central role in interpretation of model outputs, in evaluation of future climate changes expected from various scenarios, and it is closely linked to attribution of currently observed climate changes. An ongoing challenge to models and to climate projections has been to better define this key parameter and to understand the differences in computed values between various models. Climate system The system consisting of the atmosphere, hydrosphere, lithosphere, and biosphere, determining the Earth’s climate as the result of mutual interactions and responses to external influences (forcing). Physical, chemical, and biological processes are involved in interactions among the components of the climate system. (AMS) Coupled Model A class of analytical or numerical time-dependent models in which at least two different subsystems of Earth’s climate system are allowed to interact. These subsystems may include the atmosphere, hydrosphere, cryosphere, and biosphere. This term is most commonly used for models of the evolution and interaction of Earth’s atmosphere and ocean. Coupled (two-way) interaction between different subsystems can be contrasted with the class of models in which the evolution of subsystem A is affected by the present state of subsystem B, but changes in A do not feed back on the evolution of B itself. (AMS) CMDL Climate Monitoring and Diagnostics Laboratory Cryosphere That portion of the Earth where natural materials (water, soil, etc.) occur in frozen form. Generally limited to the polar latitudes and higher elevations. (AMS)

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties CSM Climate System Model CTM Chemical transport model Direct forcing Climate forcing that directly effects the radiative budget of the Earth’s climate system. For example, this perturbation may be due to a change in concentration of the radiatively active gases, a change in solar radiation reaching the Earth, or changes in surface albedo. Radiative forcing is reported in the climate change scientific literature as a change in energy flux at the tropopause, calculated in units of watts per square meter (W m−2); model calculations typically report values in which the stratosphere was allowed to adjust thermally to the forcing under an assumption of fixed stratospheric dynamics. DSCOVR Deep Space Climate Observatory DVI Dust veil index EBM Energy Balance Model ECHAM GCM based on European Centre for Medium-Range Weather Forecasting forecast models, modified and extended in Hamburg ECMWF European Centre for Medium-Range Weather Forecasts EDGAR Emissions Database for Global Atmospheric Research Efficacy The ratio of the climate sensitivity parameter λ for a given forcing agent to λ for a doubling of CO2 . The efficacy E is then used to define an effective forcing Fe = f E. ENSO El Niño/Southern Oscillation EOS Earth Observing System ERBE Earth Radiation Budget Experiment ERBS Earth Radiation Budget Satellite Evapotranspiration The combined processes, including physical evaporation and transpiration, through which water is transferred to the atmosphere from open water and ice surfaces, bare soil, and vegetation that make up the Earth’s surface. Over bare soils or the ocean, only physical evaporation occurs. FN Freezing nuclei GCM General circulation model GCR Galactic cosmic rays GDP Gross domestic product

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties General circulation model A time-dependent numerical model of the atmosphere. The governing equations are the conservation laws of physics expressed in finite-difference form, spectral form, or finite-element form. Evolution of the model circulation is computed by time integration of these equations starting from an initial condition. A GCM can be used for weather prediction or for climate studies. (AMS) Geological timescale Time as considered in terms of the history of the Earth. It is divided into geologic eras, periods, and epochs. Depending on the part of the geologic timescale, increments are as long as tens of millions of years or as short as hundreds of years. In general, geologic time is more finely divided closer to the present. (AMS) Global warming potential (GWP) An index describing the radiative characteristics of well-mixed greenhouse gases that represents the combined effect of the differing times these gases remain in the atmosphere and their relative effectiveness in absorbing outgoing infrared radiation. This index approximates the time-integrated warming effect of a unit mass of a given greenhouse gas in today’s atmosphere, relative to that of carbon dioxide. GPS Global positioning system Greenhouse gases Those gases, such as water vapor, carbon dioxide, ozone, methane, nitrous oxide, and chlorofluorocarbons, that are fairly transparent to the short wavelengths of solar radiation but efficient at absorbing the longer wavelengths of infrared radiation emitted by the Earth and atmosphere. Trapping of heat by these gases controls the Earth’s surface temperature, despite their presence in only trace concentrations in the atmosphere. Anthropogenic emissions are important additional sources for all except water vapor. Water vapor, the most important greenhouse gas, is thought to increase in concentration in response to increased concentrations of the other greenhouse gases as a result of feedbacks in the climate system. (AMS) GRIP/GISP Greenland Ice Core Project/Greenland Ice Sheet Project Holocene epoch The last 10,000 years of geologic time. Hygroscopicity The relative ability of a substance (as an aerosol) to adsorb water vapor from its surroundings and ultimately dissolve. (AMS) IGACO Intergrated Global Atmospheric Chemistry Observation System IIASA International Institute for Applied Systems Analysis IMAGE Integrated Model to Assess the Greenhouse Effect Indirect radiative forcing A climate forcing that creates a radiative imbal-

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties ance by first altering climate system components (e.g., precipitation efficiency of clouds), which then almost immediately lead to changes in radiative fluxes. Examples include the effect of solar variability on stratospheric ozone and the modification of cloud properties by aerosols. INDOEX Indian Ocean Experiment Infrared radiation That portion of the electromagnetic spectrum lying between visible light and microwaves. The wavelength range is approximately between 720 and 1 μm. In meteorology, this range is often further divided into the solar infrared and terrestrial radiation, with the division occurring around 4 μm. Dominant absorbers of infrared radiation include the Earth’s surface, clouds, water vapor, and carbon dioxide. According to Kirchhoff’s law, these are also good emitters of infrared radiation. (AMS) IPAT The I = P × A × T framework hypothesizes that environmental impact (I) is determined by the interacting effects of population size (P), per capita consumption levels (A, for affluence), and finally the per capita pollution generated by the technology (T) used to satisfy the consumption levels. IPCC Intergovernmental Panel on Climate Change IR Infrared ISCCP International Satellite Cloud Climatology Project LAI Leaf area index Latent heat The specific enthalpy difference between two phases of a substance at the same temperature. The latent heat of vaporization is the water vapor-specific enthalpy minus the liquid water-specific enthalpy. When the temperature of a system of dry air and water vapor is lowered to the dewpoint and water vapor condenses, enthalpy released by the vapor heats the air vapor liquid system, reducing or eliminating the rate of temperature reduction. Similarly, when liquid water evaporates, the system must provide enthalpy to the vapor by cooling. The latent heat of fusion is the specific enthalpy of water minus that of ice, and the latent heat of sublimation is the specific enthalpy of water vapor minus that of ice. (AMS) LBA Large-scale Biosphere-Atmosphere Experiment in Amazonia LIP Large igneous province Longwave radiation In meteorology, a term used loosely to distinguish radiation at wavelengths longer than about 4 μ, usually of terrestrial origin, from that at shorter wavelengths (shortwave radiation), usually of solar origin. (AMS)

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties MARIA Multiregional Approach Resource and Industry Allocation MESSAGE Model for Energy Supply Strategy Alternatives and General Environmental Impact MiniCAM Mini Climate Assessment Model MODIS Moderate Resolution Imaging Spectroradiometer MSU Microwave Sounding Unit MWR Microwave Radiometer NACP North American Carbon Program NAM Northern Annular Mode NAO North Atlantic Oscillation NASA GISS National Aeronautics and Space Administration Goddard Institute for Space Studies NCEP National Centers for Environmental Prediction NIST National Institute of Standards and Technology NMVOC Non-methane volatile organic compounds Nonradiative forcing A climate forcing that creates an energy imbalance that does not immediately involve radiation. An example is the increasing flux resulting from agricultural irrigation. NPOESS National Polar-orbiting Operational Environmental Satellite System NRC National Research Council NWP Numerical Weather Prediction OCO Orbiting Carbon Observatory OECD Organization for Economic Cooperation and Development Optical depth The optical thickness measured vertically above some given altitude. Optical depth is dimensionless and may be used to specify many different radiative characteristics of the atmosphere. (AMS) PBL Planetary boundary layer PCM Parallel Climate Model PETM Paleocene-Eocene Thermal Maximum POLDER Polarization and Directionality of the Earth’s Reflectances

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties Projections of climate change An estimate of future climate, typically produced by a climate model, in response to estimates of future natural and anthropogenic forcings. Note that most projections consider only a subset of possible forcings. Proxy data Data gathered from natural recorders of climate variability (e.g., tree rings, ice cores, fossil pollen, ocean sediments, coral and historical data). By analyzing records taken from these and other proxy sources, scientists can extend understanding of climate far beyond the 140-year instrumental record. PSC Polar stratospheric cloud QBO Quasi-Biennial Oscillation Radiative forcing See direct radiative forcing; indirect radiative forcing RCCP Regional climate change potential RCE Radiative-convective equilibrium Sensible heat The outcome of heating a surface without evaporating water from it. Sensible heat per unit mass can be identified roughly with the specific enthalpy of unsaturated air, that is, approximately cpdT, where cpd is the specific heat of dry air at constant pressure and T is temperature. Sensible heat is often compared with latent heat, which is the difference between the enthalpy of water vapor and that of liquid water. (AMS) Shortwave radiation In meteorology, a term used loosely to distinguish radiation in the visible and near-visible portions of the electromagnetic spectrum (roughly 0.4 to 4.0 μm in wavelength), usually of solar origin, from that at longer wavelengths (see longwave radiation), usually of terrestrial origin. (AMS) SIRCUS Spectral Irradiance and Radiance Calibrations with Uniform Sources Solar insolation The amount of electromagnetic energy (solar radiation) incident on the surface of the Earth, generally expressed in kW h m−2 day−1. (AMS) Solar irradiance The amount of solar energy that arrives at a specific area of a surface during a specific time interval (radiant flux density). A typical unit is W m−2. SORCE Solar Radiation and Climate Experiment SRES Special Report on Emissions Scenarios produced by the IPCC. (Nakićenović, 2000)

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties SST Sea surface temperature Stratosphere The region of the atmosphere extending from the top of the troposphere (the tropopause, located at roughly 10-17 km above the surface) to the base of the mesosphere (the stratopause, located at roughly 50 km above the surface). The stratosphere is characterized by constant or increasing temperatures with increasing height and marked vertical stability. It owes its existence to heating of ozone by solar UV radiation, and its temperature varies from 85°C or less near the tropical tropopause to roughly 0°C at the stratopause. Although the major constituents of the stratosphere are molecular nitrogen and oxygen, just as in the troposphere, the stratosphere contains a number of minor chemical species that result from photochemical reactions in the intense ultraviolet radiation environment. Chief among these is ozone, whose presence shelters the underlying atmosphere and the Earth’s surface from exposure to potentially dangerous UV radiation. (AMS) TAR IPCC Third Assessment Report TARFOX Tropospheric Aerosol Radiative Forcing Observational Experiment Teleconnection (1) A linkage between weather changes occurring in widely separated regions of the globe. (2) A significant positive or negative correlation in the fluctuations of a field at widely separated points. Most commonly applied to variability on monthly and longer timescales, the name refers to the fact that such correlations suggest that information is propagating between the distant points through the atmosphere. (AMS) TES Tropospheric Emission Spectrometer THC Thermohaline circulation TOA Top of the atmosphere TOMS Total Ozone Mapping Spectrometer TOPEX Topography Experiment for Ocean Circulation Tropopause The boundary between the troposphere and stratosphere, usually characterized by an abrupt change of lapse rate. The change is in the direction of increased atmospheric stability from regions below to regions above the tropopause. Its height varies from 15 to 20 km (9 to 12 miles) in the Tropics to about 10 km (6 miles) in polar regions. (AMS) Troposphere That portion of the atmosphere from the Earth’s surface to the tropopause—that is, the lowest 10-20 km (6-12 miles) of the atmosphere—and the portion of the atmosphere at which most weather occurs.

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties The troposphere is characterized by decreasing temperature with height, appreciable vertical wind motion, appreciable water vapor, and weather. (AMS) TSI Total solar irradiance Twomey effect The increase in cloud albedo due to an increase in aerosol concentration. For a dynamic forcing that creates a cloud with a given vertical extent and liquid water content, an increase in aerosol concentration going into the cloud can result in the formation of a larger number of smaller droplets compared to an unperturbed cloud. The end result is an increase in cloud albedo. UARS Upper Atmosphere Research Satellite UV Ultraviolet VEI Volcanic Explosivity Index Velocity potential A scalar function with its gradient equal to the velocity vector of an irrotational flow. VOC Volatile organic compound

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