The Convention on Biological Diversity (CBD) defines biological diversity (= biodiversity) as "the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems." (Article 2.)
and of ecosystems.
Biodiversity is unequally distributed across space. Different places are of importance for biodiversity for many different reasons, e.g. as nesting or feeding sites for one single species, because of the large number of species or ecosystem types occurring in an area, or due to the rarity or threatened status of the species or ecosystems present.
Several different criteria have been used in varying combinations to identify priority areas for biodiversity conservation. The criteria include species richness, the occurrence of endemic or endangered species, and the degree of threat or percentage of original habitat area that has already been destroyed. Examples of schemes that apply combinations of these criteria at global scale include: Centres of Plant Diversity; Biodiversity Hotspots; and Alliance for Zero Extinction sites. These efforts are useful for identifying global priorities, but national and site-scale decision-making requires more detailed data and appropriately scaled prioritisation analyses.
Biodiversity and climate change are closely interlinked. Biodiversity is crucial to the ability of both people and the biosphere to adapt to climate change. It is also vital for climate change mitigation (through carbon sequestration and storage). However, biodiversity is also threatened by climate change, including through changing precipitation and rising temperature. Therefore, it is essential that biodiversity and its vulnerability are taken into account in adaptation and mitigation strategies.