IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

critically endangered (CR or sometimes CE)

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

is one that has been categorized by the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

as facing an extremely high risk of

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

in the wild. As of December 2023, of the 157,190 species currently on the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

Red List, 9,760 of those are listed as critically endangered, with 1,302 being possibly extinct and 67 possibly

extinct in the wild A species that is extinct in the wild (EW) is one that has been categorized by the International Union for Conservation of Nature as only consisting of living members kept in captivity or as a naturalized population outside its historic range ...

. The

provides the public with information regarding the conservation status of animal, fungi, and plant species. It divides various species into seven different categories of conservation that are based on habitat range, population size, habitat, threats, etc. Each category represents a different level of global extinction risk. Species that are considered to be critically endangered are placed within the "Threatened" category. As the IUCN Red List does not consider a species extinct until extensive targeted surveys have been conducted, species that are possibly extinct are still listed as critically endangered. IUCN maintains a list of "possibly extinct" and "possibly extinct in the wild" species, modelled on categories used by

BirdLife International BirdLife International is a global partnership of non-governmental organizations that strives to conserve birds and their habitats. BirdLife International's priorities include preventing extinction of bird species, identifying and safeguarding i ...

to categorize these

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

Criteria

To be defined as critically endangered in the Red List, a species must meet ''any'' of the following criteria (A–E) ("3G/10Y" signifies three generations or ten years—whichever is longer—over a maximum of 100 years; "MI" signifies Mature Individuals): :A: Population Size Reduction :# The rate of reduction is measured either over a 10 year span or across three different generations within that species. :# The cause for this decline must also be known. :# If the reasons for population reduction no longer occur and can be reversed, the population needs to have been reduced by at least 90% :# If not, then the population needs to have been reduced by at least 80% :B: Reduction Across a Geographic Range :# This reduction must occur over less than 100 km² OR the area of occupancy is less than 10 km². :## Severe

habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...

or existing at just one location :## Decline in extent of occurrence, area of occupancy, area/extent/quality of habitat, number of locations/subpopulations, or amount of MI. :## Extreme fluctuations in extent of occurrence, area of occupancy, number of locations/subpopulations, or amount of MI. :C: Population Decline :# The population must decline to less than 250 MI and either: :## A decline of 25% over 3G/10Y :## Extreme fluctuations, or over 90% of MI in a single subpopulation, or no more than 50 MI in any one subpopulation. :D: Population Size Reduction :# The population size must be reduced to numbers of less than 50 MI. :E: Probability of Extinction :# There must be at least a 50% probability of going extinct in the wild within over 3G/10Y

Causes

The current extinction crisis is witnessing extinction rates that are occurring at a faster rate than that of the natural extinction rate. It has largely been credited towards human impacts on

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

and the

loss of biodiversity Biodiversity loss happens when plant or animal species disappear completely from Earth (extinction) or when there is a decrease or disappearance of species in a specific area. Biodiversity loss means that there is a reduction in biological dive ...

. This is along with natural forces that may create stress on the species or cause an animal population to become extinct. Currently the biggest reason for species extinction is human interaction resulting in habitat loss. Species rely on their habitat for the resources needed for their survival. If the habitat becomes destroyed, the population will see a decline in their numbers. Activities that cause loss of habitat include

pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

urbanization Urbanization (or urbanisation in British English) is the population shift from Rural area, rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. ...

, and

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

. Another reason for plants and animals to become endangered is due to the introduction of

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

. Invasive species invade and exploit a new habitat for its natural resources as a method to outcompete the native organisms, eventually taking over the habitat. This can lead to either the native species' extinction or causing them to become endangered, which also eventually causes extinction. Plants and animals may also go extinct due to disease. The introduction of a disease into a new habitat can cause it to spread amongst the native species. Due to their lack of familiarity with the disease or little resistance, the native species can die off.

References

{{Threatened species by region, state=collapsed IUCN Red List Biota by conservation status