Book 2.indb - US Climate Change Science Program

Abrupt Climate ChangeGLOSSARY, ACRONYMS, AND ABBREVIATIONSGLOSSARYAblation – Loss of snow and ice, primarily bymelting and calving.Abrupt climate change – A large-scale changein the climate system that takes place over a fewdecades or less, persists (or is anticipated to persist)for at least a few decades, and causes substantialdisruptions in human and natural systems.Albedo – The fraction of solar radiation reflectedby a surface or object, often expressed as a percentage.Anthropogenic – Resulting from or produced byhuman beings.Atlantic Meridional Overturning Circulation(AMOC) – A northward flow of warm, salty waterin the upper layers of the Atlantic, and a southwardflow of colder water in the deep Atlantic.Clathrate – A substance in which a chemical latticeor cage of one type of molecule traps anothertype of molecule.Climate system – The climate system is thehighly complex system consisting of five majorcomponents: the atmosphere, the hydrosphere, thecryosphere, the land surface, and the biosphere, andthe interactions between them. The climate systemevolves in time under the influence of its own internaldynamics and because of external forcingssuch as volcanic eruptions, solar variations, andanthropogenic forcings such as the changing compositionof the atmosphere and land use change.Climate feedback – An interaction mechanismbetween processes in the climate system is calleda climate feedback when the result of an initialprocess triggers changes in a second process thatin turn influences the initial one. A positive feedbackintensifies the original process, and a negativefeedback reduces it.Climate model – A numerical representation ofthe climate system based on the physical, chemical,and biological properties of its components, theirinteractions and feedback processes, and accountingfor all or some of its known properties.Climate variability – Climate variability refers tovariations in the mean state and other statistics (suchas standard deviations, the occurrence of extremes,etc.) of the climate on all spatial and temporal scalesbeyond that of individual weather events. Variabilitymay be due to natural internal processeswithin the climate system (internal variability), orto variations in natural or anthropogenic externalforcing (external variability).Cryosphere – The component of the climate systemconsisting of all snow, ice, and frozen ground(including permafrost) on and beneath the surfaceof the Earth and ocean.Downscaling – A method that derives local- toregional-scale (10 to 100 km) information fromlarger scale models or data analyses.El Niño Southern Oscillation (ENSO) – The termEl Niño was initially used to describe a warm-watercurrent that periodically flows along the coast of Ecuadorand Perú, disrupting the local fishery. It hassince become identified with a basin-wide warmingof the tropical Pacific Ocean east of the dateline.This oceanic event is associated with a fluctuationof a global-scale tropical and subtropical surfacepressure pattern called the Southern Oscillation.This coupled atmosphere-ocean phenomenon,with preferred time scales of 2 to about 7 years, iscollectively known as the El Niño Southern Oscillation(ENSO). It is often measured by the surfacepressure anomaly difference between Darwin andTahiti and the sea surface temperatures in the centraland eastern equatorial Pacific. During an ENSOevent, the prevailing trade winds weaken, reducingupwelling and altering ocean currents such that thesea surface temperatures warm, further weakeningthe trade winds. This event has a great impact onthe wind, sea surface temperature, and precipitationpatterns in the tropical Pacific. It has climaticeffects throughout the Pacific region and in manyother parts of the world, through global teleconnections.The cold phase of ENSO is called La Niña.Forcing – Any mechanism that causes the climatesystem to change or respond.241