site-wide glossary for terms
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Related to humans or resulting from human influences. 


"The envelope of gases that surrounds a planet and is held to it by the planet's gravitational attraction. The earth's atmosphere is mainly oxygen and nitrogen."

Ahrens, Donald C. Meteorology Today: An Introduction to Weather, Climate, and the Environment. 5th ed. St Paul: West, 1994, pg. 566




The number of different species of plants and/or animals living in a given region. Biodiversity is considered to be important for multiple reasons. Ecosystems with high biodiversity are more likely to be able to recover from disturbances than ecosystems with low biodiversity. Furthermore, a larger variety of species available for study means there is a greater chance that some of those species could be of benefit to humankind. Finally, some individuals believe that biodiversity should be protected for its own sake, for ethical or aesthetic reasons. 

Biological Invasion

When a species moves into an area where it was not formerly present and establishes successful colonies, sometimes displacing native species in the process. Also see invasive species.


"The term biosphere can be used one of two ways. It can either refer to the part of the Earth system comprising all ecosystems and living organisms in the atmosphere and on land (terrestrial biosphere), or [it can refer to all ecosystems and living organisms] in the oceans (marine biosphere), including derived dead organic matter, such as litter, soil organic matter, and oceanic detritus."

IPCC: Climate Change 2007, Working Group II: "Impacts, Adaptation and Vulnerability," Glossary A-D.

Boundary Layer

"The layer of air from the earth's surface usually up to about 1km (3300 ft) [above the surface] where the wind is influenced by friction of the earth's surface and objects on it."

(Ahrens, Donald C. Meteorology Today: An Introduction to Weather, Climate, and the Environment. 5th ed. St Paul: West, 1994, pg. 566.)


In science, the term budget is used in a way similar to how it is used in the world of finance -- an estimate of quantity of income and expense. A budget is balanced when inputs are equal to outputs. For example, in the Earth's carbon cycle there are stocks or reservoirs of carbon, and there are exchanges between these stocks, such as carbon stored in the ocean or terrestrial biosphere, and there are rates of exchange, such as with the atmosphere. Altogether these reservoirs and exchanges represent the carbon budget.  When a stock is taking up carbon, it is a sink; when it is giving off carbon, it is a source.



When a species spreads to and establishes a successful population in a new habitat. 



The term deficit refers to a shortage or less-than-usual quantity of a given item.


"The conversion of forested areas to non-forested areas, which include crops, pastures, and urban areas. Deforestation releases CO2 sequestered in trees and soil into the atmosphere. It also changes the nature of ecosystem services provided."




In the context of climate science, "emissions" refers to gases being released into the atmosphere. Most commonly, climate scientists mean specifically gases released during the extraction or burning of fossil fuels, but gases can also be released by natural processes, such as those released during permafrost melt. 


"The process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. These typically promote excessive growth of algae. As the algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other organisms, such as fish. Eutrophication is a natural, slow-aging process for a water body, but human activity greatly speeds up the process." 

(Art, 1993. "Toxic Substances Hydrology Program: Eutrophication." USGS.


False Spring

A false spring is when warm weather occurs early in the spring, followed by a return of colder, winter-like conditions. 


Feedback refers to when an alteration in a process in a system occurs that impacts the state of the system. There are two types of feedback: postive feedback (amplifying feedback) and negative feedback (stabilizing feedback).

A positive, or augmenting, feedback is when a change in one part of a system amplifies a change in another part, pushing the system into a continuous loop that shifts the system in the same direction as the initial change in process. In other words, an initial warming of a system would cause the system to coninue getting increasingly warmer, or an initial cooling of a system would cause the system to become increasingly cooler. 

A negative, or stabilizing, feedback is when a change in a process dampens the recurrence of that change in the system, pushing the system to counteract the direction of the initial process.  In other words, added warming in a system would cause the system to respond in such a way that cooling would result, stabilizing the system, and returning it to a state close to equilibrium.

In climate science, an example of a positive feedback is loss of sea-ice and how it changes the albedo, or reflectivity, of the Earth.  Sea ice is highly reflective, and exposed ocean is dark. As the climate warms, sea ice may melt. As the ice melts, the surface area of that region moves from being reflective (white) to being darker open ocean, which absorbs rather than reflects the sun's radiaion. Since more radiation is being absorbed, surface temperatures will rise, leading to increased warming and more loss of sea ice. Therefore, in this instance, heating the system pushes the system to continue to warm.

Fossil Fuels

"Hydrocarbon fuels derived from fossil carbon deposits such as coal, oil, and natural gas." (IPCC glossary) 


Fuels of this type are called fossil fuels because they are made up of carbon deposits from dead organic matter that was decomposed in anaerobic (without oxygen) conditions over hundreds of thousands of years.  For example, many coal deposits were formed during the Carboniferous Period about 360 to 300 million years ago. (AGCI)



Ground Truthing

Ground truthing is when scientists double-check their data by visiting a study site in person, or "on the ground." It is an important process used by scientists to test the accuracy a model or statistical analysis in real life and make certain that assumptions they have made or parameters they are using are correct. 



The quality of being non-uniform. For example, a heterogeneous landscape contains multiple types of land-cover, such as some forested areas and some grasslands. Homogeneity is the quality of being uniform, such as a region that is entirely forested or entirely grassland. 


A living organism that cannot produce energy using photosynthesis or similar chemical processes. All consumers are heterotrophs. Examples include humans, insects, and some forms of bacteria or fungi.


The relationship and interaction between the hydrosphere (liquid water on and under Earth's surface) and meteorolgy (the study of the lower level of Earth's atmosphere). 


"The component of the climate system made up of liquid surface and ground water, such as oceans, seas, rivers, fresh water lakes, underground aquifers, etc."

(IPCC Climate Change 2007: Working Group I: The Physical Science Basis, Glossary E-O)


Introduced Species

A species living in an area where it was not native and which was brought into the area, intentionally or unintentionally, through human actions. 

Invasive Species

A loosely used term employed to describe a species that has successfully established populations in an area where it is not native. Invasive species are of concern to ecologists because they often outcompete or displace native species, possibly leading to an eventual decline in biodiversity. They can also have impacts on human activities. For example: thickly growing bind-weeds may cover human structures. The term invasive species is sometimes used interchangeably with the terms introduced species, non-native species, or exotic species. 


IPCC stands for the Intergovernmental Panel on Climate Change. The IPCC was founded by the United Nations Environmental Program and the World Meteorlogical Association in 1988. The IPCC is a scientific organization committed to reveiwing and assessing "the most recent scientific, technical and socio-economic information produced worldwide relevant to the understanding of climate change." It does not conduct any research itself, and the information and assessments it provides are drawn from work contributed by thousands of scientists from across the world.


Land Use Change

Land use refers to the state of a large area of land in relation to multiple factors: human uses of the landscape, such as agriculture or city development; wild animal use of the landscape; and vegetation on the land, such as forest, desert, or grassland.

Latent Heat

"The heat that is either released or absorbed by a unit of mass of a substance when it undergoes a change in state, such as during evaporation, condensation, or sublimation."

(Ahrens, Donald C. Meteorology Today: An Introduction to Weather, Climate, and the Environment. 5th ed. St Paul: West, 1994, pg. 572.)

Limiting Nutrient

An element or compound that a living thing needs for growth or survival but which is not readily available in the quantity needed relative to other necessary nutrients. During growth, the available pool of this component will be the first to be used up, causing growth to stop, thereby limiting number of individual plants or amount of plant growth in a given area.


Land Use, Land Change and Forestry, a sub-organization of the United Nations.


Native Plant

A native plant is "any plant which is a member of a species which was present at a given site prior to European contact."

(California Native Plant Society. 1996. "Policy on Invasive Plants." Document Archive, Sept. 1996.


Ocean Acidification

The oceans form an important component of the global carbon cycle. Oceans take up between 30-40% of carbon dioxide added to the atmosphere each year. Carbon dioxide (CO2) natrually dissolves in water, and the higher the concentration of CO2 in the atmosphere, the more CO2 will be taken up by lakes and oceans until they become CO2 saturated and cannot take up any more of that form of gas. Once the CO2 is dissolved in the ocean, some of it undergoes a chemical reaction with the water. Depending on the pH of the water, it will either form carbonic acid (H2CO3) or Hydrogen ions (H+) and bicarbonate (HCO3-). Because the concentration of CO2 in the atmosphere has increased sharply in recent years, the concentration of CO2 in the ocean has also increased. The more CO2 that is in the ocean, the more acidic the ocean is likely to be as the CO2 reacts to form carbonic acid. This process is known as ocean acidification.

Ocean acidification may have direct impacts on oceanic life, for example, making it difficult for mollusks to form shells. Furthermore, cold water has a higher capacity to store dissolved gas than warm water does, so it is possible that as the oceans warm, their ability to take Carbon dioxide out of the atmosphere may decrease, leading to an even greater rise of CO2 in the atmosphere and, therefore, an even steeper rate of global atmospheric warming than would otherwise occur.


Phosphorus is a nutrient essential to the formation of RNA and essential for growth and survival, whose chemical symbol is P. Plants remove phosphorus from the soil and process it into a form that is usable by herbivores and omnivores. 
Although humans generally get enough of it in our diets, the demand for phosphorus by plants is very high relative to the supply of it in soils. Thus, in many instances around the world, the availability of phosphorus limits how much plant or algea growth can take place in a given area. For this reason, phosphorus is considered by ecologists to be a limiting nutrient. 
Phosphorus develops in soils over long periods of time as rock is weathered and minerals are dissolved to become available for use by plants. In addition to this, some phosphorus can blow in from other areas in the form of dust or be made available during the decomposition of organic matter (such as waste, or a dead animal or plant). Scientists refer to the amount of phosphorus that is available in an area of soil as a “pool.” The size of this pool is determined by the rate of inflow from weathering, dust, ands decomposition relative to the outflow from leaching and erosion. 
Models of the phosphorus cycle were developed in the 1970s as ecologists started making estimates of the various pools of P in the Earth system (such as in land, freshwater, and oceans) then developing estimates of fluxes between these pools. These estimates often have grounding in various site specific observations, but due to the enormity of  the Earth system, scientists must characterize quantities at broader scale based on inferences from their limited observations.

Scientists refer to the amount of an element or compound that is available in a given area of soil, vegetation, or water as a pool. The size of this pool is determined by the rate of input (such as from weathering, dust, decomposition, or fixation) relative to the outflow (such as from leaching, erosion, burning, or other forms of release). A word that scientists use in a similar way to the word pool is stock.

Population Level Evolution

A change in the genetic ratio in one or a few populations of a given species that has many different populations. The change can either be the creation of a new gene, if a mutagen is present, or it can be increased prevalence of an uncommon, pre-existing gene selected by environmental factors. 

Population Level Extinction

Population extinction is when all the individuals in a single population of a species have died, but the species still persists in other populations found in other locations. 


Semi Arid

Semi-Arid regions are geographic areas that receive between 10-20 inches of rainfall per year. They receive more rain than deserts but are still characterized by dry conditions and plants tolerant of limited water availability.

Sensible heat

"The heat we can feel and measure with a thermometer."

(Ahrens, Donald C. Meteorology Today: An Introduction to Weather, Climate, and the Environment. 5th ed. St Paul: West, 1994, pg. 575.)


Sequestration refers to the long-term storage of an element or compound in a form where it is unlikely to escape from its current state and position in its cycle to another state or location. For example, carbon sequestration can occur when carbon dioxide (CO2) is taken out of the atmosphere and buried deep under layers of ocean sediments. Because thousands of years will pass before the CO2 will be released from these sediments, it is being stored, or "sequestered" in this location. Sequestration of a substance can also involve a change of state, for example from a gas to a liquid or solid.


In science, particularly in relation to the cycles of elements such as carbon or nitrogen, a sink is a reservoir that stores a substance for a period of time. For example, the ocean can function as a sink, storing carbon from the atmosphere. The term sink may also refer to an area where there is a decreasing population of a given species.



A source refers to the part of a system that is adding more of a given item to the system, such as more carbon being added to the atmosphere. For example, combustion of wood is a source of carbon dioxide to the atmosphere

The term source can also refer to an area where more individuals of a species are surviving to reproduce than die each year.


Stock is the amount of something available in a system. It could be nutrients in the soil, water in a bathtub, or money in a bank. The amount of stock in a system is determined by the history of inflow and outflow to that pool--how much of your item is entering the system, minus how much of that item is leaving it. The term stock is sometimes used interchangeably with the word pool. For exercises on unstanding inflow, outflow and stock try visiting the SEED educational website.


Temperature Isotherm

An isotherm is a line on a map connecting points that have roughly equal temperatures. Regions near the equator tend to be warmer than regions at high latitudes, and regions that are closer to sea-level tend to be warmer than regions at high elevation. As a result, temperature tends to decrease as you go up in latitude or elevation (or both).


The term threshold describes a barrier or a point beyond which significant changes will occur.

Timing Mismatch

In biology, the term "timing mismatch" refers to a disconnect between two related ecological occurrences that formerly occurred at the same time. For example, some insects whose larvae are dependent on a specific type of plant for food, must reach the growth stage of their lifecycle at the same time as when the most plant matter is available in order to survive. If the food source blooms or dries up earlier in the year than usual, but the larvae reach their growth stage at the same time of year as previously, then there is a "timing mismatch" where growth of the larvae does not coincide with the best availability of their food source. As a result, the larvae will struggle to find enough food to survive through their next phase. 

Timing mismatches can be caused by shifts in regional climate (e.g. warm weather coming early each Spring) or unusual climate events (a single season with several unusually warm days). Plants may alter their cycles directly in response to such changes, while animals may be slower to respond. The result is that timing for one species may speed up while another species continues on the timing of its previous cycles, creating a mismatch of events. Watch clips from Camille Parmesan to learn more about this situation. 


Water Table

The depth under the surface of the ground at which water can be found. When water use in an area is higher than the amount of water recharged through rainfall or snowmelt soaking into the ground, then the water table may be diminished or occur deeper under ground than it did before. In other words, excessive use can drop the water table.


A watershed is an area of land where all the water flows to one place.  This includes the rivers in a given area, and it also includes land connected by runoff or groundwater. The boundaries of a watershed are determined by local high points of land, over which water cannot flow.