Glossary

(1) The combined processes (such as sublimation, fusion or melting, evaporation) that remove snow or ice from the surface of a glacier or from a snow-field; also used to express the quantity lost by these processes. (2) Reduction of the water equivalent of a snow cover by melting, evaporation, wind and avalanches.

The uptake of radiation by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted.

All processes by which snow or ice are added to a glacier. This is typically the accumulation of snow, which is slowly transformed into ice; other accumulation processes can include avalanches, wind-deposited snow, and the freezing of rain within the snow pack.

Necessary changes to protect oneself, structures and communities from the effects of sea level rise.

The ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation, or placed in an instrument shelter 1.5 to 2 meters above ground; also called surface temperature.

A non-dimensional, unitless quantity that measures how well a surface reflects solar energy; ranges from 0 to 1. A value of 0 means the surface is a “perfect absorber,” where all incoming energy is absorbed. A value of 1 means the surface is a “perfect reflector,” where all incoming energy is reflected and none is absorbed.

A technique for measuring height. Satellite radar altimetry measures sea surface height, and it has also been used to measure the height of ice surfaces. Satellite laser altimetry measures the height of ice surfaces (land and sea ice). For example, radar altimetry measures the time taken by a radar pulse to travel from the satellite antenna to the sea surface and back to the satellite receiver. Combined with precise satellite location data, and information on the medium through which the radar pulse travelled (water vapor content of the atmosphere, electron content of the ionosphere, etc.), altimetry measurements yield highly accurate sea-surface heights.

Earth’s southernmost and fifth largest continent, containing the geographic South Pole and the Antarctic ice sheet.

An ocean current that flows eastward around Antarctica, "pushed" by the strong winds at those southern latitudes.

The largest single mass of ice on Earth. It covers an area of almost 14 million km² and contains 26-30 million km³ of ice, an amount equivalent to approximately 70 meters of sea level in the world’s oceans. The ice sheet rests on a major landmass in East Antarctica, but in West Antarctica the bed is in places more than 2,500 meters below sea level. It would be seabed if the ice sheet were not there.

The northernmost element of mainland Antarctica, between longitudes  78^oW and 55^oW, approximately.  It is the only part of the continent of Antarctica that extends outside of the Antarctic Circle. It is approximately 1,200 miles (2,000 km) long, stretching from 75°S (as drawn between Cape Adams [Weddell Sea] and a point on the mainland south of Eklund Islands) to 63°S (Prime Head on the Trinity Peninsula). The southern tip of South America, Cape Horn, is about 610 miles (980 km) farther north, and is separated by the Drake Passage.

Human-caused or -produced.

A body of saturated rock through which water can easily move. Aquifers must be both permeable and porous and include such rock types as sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel. Fractured volcanic rocks such as columnar basalts also make good aquifers. The rubble zones between volcanic flows are generally both porous and permeable and make excellent aquifers.

The smallest ocean, c.5,400,000 mi² (13,986,000 km²), located entirely within the Arctic Circle and occupying the region around the North Pole. Due to the low air temperatures, the Arctic Ocean has a large sea ice cover in winter and a smaller amount at the end of summer.

A global array of nearly 4,000 free-drifting floats that measures the temperature and salinity of the upper 2,000 meters (6,500 feet) of the ocean. The data are made public with hours of collection.

Tides (the rise and fall of sea levels) that result from gravitational effects related to the Earth, Sun, and Moon, without any atmospheric influences.

The body of salt water covering approximately one-fifth of Earth’s surface and separating the continents of Europe and Africa to the east from those of North and South America to the west. The ocean’s name, derived from Greek mythology, means the “Sea of Atlas.” It is second in size only to the Pacific Ocean.

The mixture of gases surrounding the Earth. The Earth's atmosphere consists of about 79.1 percent nitrogen (by volume), 20.9 percent oxygen, 0.036 percent carbon dioxide and trace amounts of other gases. The atmosphere can be divided into a number of layers according to its mixing or chemical characteristics, generally determined by its thermal properties (temperature). The layer nearest Earth is the troposphere, which reaches up to an altitude of about 8 kilometers (about 5 miles) in the polar regions and up to 17 kilometers (nearly 11 miles) above the equator. The stratosphere, which reaches to an altitude of about 50 kilometers (31miles) lies atop the troposphere. The mesosphere, which extends from 80 to 90 kilometers (50 to 56 miles) atop the stratosphere, and finally, the thermosphere, or ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is relatively little mixing of gases between layers.

The large-scale movement of air by which heat is distributed on the surface of the Earth.

Just as the incoming and outgoing energy at the Earth's surface must balance, the flow of energy into the atmosphere must be balanced by an equal flow of energy out of the atmosphere and back to space.

The weight of the atmosphere, evidenced as surface atmospheric pressure, is sufficient to deform slightly the surface of the Earth. Since the surface pressure varies in time, so does the deformation it causes on the "solid" Earth.

An area of land that drains to a common outlet (also, watershed).

A reference to an instrument that automatically records the temperatures of water at various depths.

The solid rock that lies under the surface of the ground.

"Bias" has several interpretations. When measuring some property of the Earth, bias is a systematic distortion of a statistic as a result of sampling procedure. For example, when comparing measurements of the same properties of the Earth at the same time by two different instruments, there may be a non-zero average difference, which we call a bias. On the other hand, concerning reasoning, a positive bias, or confirmation bias, is a tendency to test a hypothesis with examples or cases that tend to confirm the initial hypothesis. 

The ability or tendency to float in water or air or some other fluid. For example, in the oceans, less dense, warmer seawater usually "floats" above colder, denser seawater, and we say the less dense water has more buoyancy.

Calving occurs when chunks of ice break off at the terminus, or end, of a glacier. Ice breaks because the forward motion of a glacier makes the terminus unstable. We call these resulting chunks of ice "icebergs."

Carbon dioxide (CO₂) is the primary greenhouse gas emitted through human activities. In 2014, CO2 accounted for about 80.9 percent of all U.S. greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals). Human activities are altering the carbon cycle–both by adding more CO₂ to the atmosphere and by influencing the ability of natural sinks, like forests, to remove CO2 from the atmosphere. While CO₂ emissions come from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution.

Climate can be thought of as the long-term average of weather. Note that not only the atmosphere is involved in weather or climate—for example, a weather event such as a hurricane is an interaction between atmosphere, ocean and land surface. Melting of an ice sheet such as Greenland is a consequence of a warming climate.

Climate change refers to any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among others, that occur over several decades or longer.

An atmospheric, oceanic, terrestrial or other process that is activated by direct climate change induced by changes in radiative forcing. Climate feedbacks may increase (positive feedback) or diminish (negative feedback) the magnitude of the direct climate change.

A quantitative way (usually implemented as a very large computer program) of representing the interactions of the atmosphere, oceans, land surface and ice. Models can range from relatively simple to quite comprehensive.

Gives an estimated range of values that is likely to include an unknown population parameter, the estimated range being calculated from a given set of sample data.

The area of seabed around a large landmass where the sea is relatively shallow compared with the open ocean. The continental shelf is geologically part of the continental crust. At the seaward edge of the continental shelf is a region of much steeper slopes, the continental slope.

The effect of Earth's rotation upon the direction of the wind or ocean currents. The Coriolis "force" turns the wind or current to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Coupled Model Intercomparison Project (CMIP) is an international effort to improve climate models by comparing multiple model simulations to observations and to each other. These comparisons can help our understanding of past and future climate changes, and also lead to climate model improvements. CMIP falls under the direction of the Working Group on Coupled Modeling, an activity of the World Climate Research Program.

A deep open crack, especially one in a glacier.

One of the interrelated components of the Earth's system, the cryosphere is frozen water in the form of snow, permanently frozen ground (permafrost), floating ice, glaciers and the continental ice sheets of Greenland and Antarctica. Fluctuations in the volume of the cryosphere cause changes in ocean sea level, which directly impact the atmosphere and biosphere.

Also "tropical cyclone," "hurricane," "typhoon": A rotating, organized cloud and storm system originating in tropical or subtropical waters, with maximum sustained winds of 74 mph or higher.

A piece of land shaped like a triangle that is formed when a river splits into smaller rivers just before it flows into an ocean.

A place where sediment carried downstream by a river enters the sea, forming a fan of sand or mud.

The density of Earth’s oceans varies over regional and global scales. Higher density water near the poles – cooler, saltier – sinks, while warmer, less-dense water in mid latitudes rises. The difference between points of higher and lower density, divided by their distance, is called a gradient; such gradients drive a large circulation pattern called the global conveyor belt. Over short horizontal distances, strong currents like the Gulf Stream and Antarctic Circumpolar Current jets are associated with strong horizontal density gradients.

Having the property of transmitting electric force without conduction; insulating.

3D representations of terrain elevation data

The action of discharging a liquid, gas or other substance.

The study of Earth’s atmosphere, lithosphere, hydrosphere, cryosphere and biosphere as a single connected system.

Models that integrate the interactions of atmosphere, ocean, land, ice and biosphere to estimate the state of regional and global climate under a wide variety of conditions.

A spectrum of models of varying complexity is used in modeling the natural Earth system. Depending on the nature of questions asked and the pertinent time scales, there are, at the one extreme, conceptual models with many simplifying assumptions, and at the other extreme, three-dimensional comprehensive models, attempting to include as many known processes (physical, biological, chemical, etc.), operating at the highest spatial and temporal resolution currently feasible. Models of intermediate complexity bridge the gap.

The eastern two-thirds of the Antarctic continent, on the Indian Ocean side of the Transantarctic Mountains. It is colder and higher than West Antarctica.

Swirling ocean current

El Niño, in its original sense, is a warm water current that periodically flows along the coast of Ecuador and Peru, disrupting local fisheries. This oceanic event is associated with a fluctuation of the intertropical surface pressure pattern and circulation in the Indian and Pacific Oceans, called the Southern Oscillation. This coupled atmosphere-ocean phenomenon is collectively known as El Niño-Southern Oscillation. During an El Niño event, the prevailing trade winds weaken and the equatorial countercurrent strengthens, causing warm surface waters in the Indonesian area to flow eastward to overlie the cold waters of the Peru current. This event has great impact on the wind, sea surface temperature, and precipitation patterns in the tropical Pacific. It has climatic effects throughout the Pacific region and in many other parts of the world. The opposite of an El Niño event is called La Niña.

A recess in a coastline forming a bay.

An endorheic basin is a closed drainage system that retains water and does not allow for overflow to other external bodies such as the rivers and or oceans. The endorheic basin may form either permanent or seasonal lakes or swamps that are maintained only through evaporation. The basin is also commonly referred to as an internal drainage system or a closed basin.

Energy is exchanged between the atmosphere and Earth's surface. Solar radiation and atmospheric longwave radiation warm the surface and provide energy to drive weather and climate. Some of this energy is stored in the ground or oceans. Some of it is returned to the atmosphere, warming the air. The rest is used to evaporate water. These surface energy fluxes are an important component of Earth’s global mean energy budget. At the global scale, Earth’s energy budget shows the atmosphere has a deficit of energy while the surface has a surplus.

The slow wearing away of the land by wind, water and ice.

In common language, an error is a mistake. In scientific parlance, an "error" is a statistical measure of the uncertainty of a measured quantity. Thus we say, for example, “3.2 mm/yr with a standard error of +/-0.4 mm/yr.”

A body of water formed where freshwater from rivers and streams flows into the ocean, mixing with the seawater. Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by the reefs, barrier islands, or fingers of land, mud, or sand that surround them.

The process by which water changes from a liquid to a gas or vapor.

The sum of evaporation from the land surface and transpiration from plants.

Unusual weather events, such as heat waves, intense precipitation, and drought. There is growing empirical evidence that warming temperatures create the conditions for these events.

Factors that increase or amplify (positive feedback) or decrease (negative feedback) the rate of a process. An example of positive climatic feedback is the ice-albedo feedback: Ice (whether on land or sea ice) is bright and reflects back much of the energy it receives from the sun, a cooling effect; as ice melts, seawater or land surfaces are darker and absorb more of the incoming energy, leading to further warming and further ice melt.

An intermediate stage in the transformation of snow to glacier ice

A narrow inlet of the sea between cliffs or steep slopes

In common language, flux means continuous change. In the physical sciences, a flux is a measure of the transport of some property in a unit of time—for example, the flux of ice through a narrowing of the land surface is measured in cubic km per year.

A process that alters the energy balance of the climate system, i.e. changes the relative balance between incoming solar radiation and outgoing infrared radiation from Earth. Such mechanisms include changes in solar irradiance, volcanic eruptions and enhancement of the natural greenhouse effect by emissions of greenhouse gases.

The initial drivers of climate, such as solar irradiance (energy from the Sun), greenhouse gas emissions, and aerosols (very small airborne particles like soot and dust)

(1) Water that is not salty, especially when considered as a natural resource. (2) Of, relating to, being or living in freshwater (not salt water).

Oceanographers use the term "freshening," meaning "decreasing salinity content."

A global, four-dimensional computer model of the climate system that can be used to simulate both natural and human-induced climate change. GCMs are highly complex and they represent the effects of such factors as reflective and absorptive properties of atmospheric water vapor, greenhouse gas concentrations, clouds, annual and daily solar heating, ocean temperatures and ice boundaries. The most recent GCMs include global representations of the atmosphere, oceans, sea ice and land surface.

Geodesy is the science of accurately measuring and understanding three fundamental properties of the Earth: its geometric shape, its orientation in space, and its gravity field— as well as the changes of these properties with time.

An abstract coordinate system with a reference surface, such as sea level, that provides known locations for surveys and maps.

The geopotential surface that best fits mean sea level.

The potential energy difference between a mass at sea level and at a given altitude, or the energy needed to move that mass from one to the other.

Heat transferred from the Earth's interior to underground deposits of dry steam (steam with no water droplets), wet steam (a mixture of steam and water droplets), hot water or rocks lying fairly close to the Earth's surface. The source of heat can be either molten lava or radioactivity.

Relating to the internal heat of the Earth.

One thousand million tons (a billion tons in the U.S.)

The ongoing movement of land once burdened by Ice Age glaciers. It is also known as "postglacial rebound."

A multi-year surplus accumulation of snowfall in excess of snowmelt on land and resulting in a mass of ice at least 0.1 km2 in area that shows some evidence of movement in response to gravity. A glacier may terminate on land or in water. Glacier ice is the largest reservoir of fresh water on Earth, and second only to the oceans as the largest reservoir of total water. Glaciers are found on every continent except Australia.

The length of the longest flow line of a glacier.

A condition occurring when melting at the front of a glacier takes place at a rate exceeding forward motion.

A function of ice temperature (a function of air and ground temperatures, with some glaciers being heated from below by geothermal heating) and the pressure of the ice.

The lower end of a glacier. If a tongue is moving dowhill faster than it is evaporating or melting, the glacier is advancing. If it is melting or evaporating faster than it can move downward, the glacier is retreating. 

When large ice pieces break into the water. See calving.

Global average sea level

A space-based navigational system of 24 or more satellites, providing continuous, worldwide coverage by broadcasting radio signals of their location, status and time.

The long-term warming of the planet. Global temperature shows a well-documented rise since the early 20th century and most notably since the late 1970s. Worldwide, since 1880 the average surface temperature has gone up by about 0.8 °C (1.4 °F), relative to the mid-20th-century baseline (of 1951-1980).

A space-borne twin satellite mission, called the Gravity Recovery and Climate Experiment (GRACE), which measures time changes in Earth’s water and ice distribution via the planet’s gravity field.

Measuring changes in a gravitational field, for example, areas of higher or lower mass on Earth's surface as measured by the twin GRACE and GRACE-FO satellites.

The field of force surrounding a body of finite mass in which another body would experience an attractive force that is proportional to the product of the masses and inversely proportional to the square of the distance between them.

Any gas that absorbs infrared radiation in the atmosphere. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, ozone, chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.

An autonomous country within the Kingdom of Denmark experiencing rapid, record-breaking ice melt. If all the ice held on Greenland were to melt, it would raise sea level by 7 meters.

With an area of 1.71 million km2 and volume of 2.85 million km3, the Greenland ice sheet is the second largest glacial ice mass on Earth.

The junction between a glacier or ice sheet and its ice shelf; the place where ice starts to float. On the ocean side of the grounding line, the ice shelf heaves up and down due to tides, while on the land side it does not.