We regularly hear of new species being discovered - does that not offset the loss of existing species?

Every year thousands of previously unknown species are discovered, described and named. Despite being 'new' to science, these plants and animals were already part of our planet's biodiversity and so cannot compensate for the loss of species we already know about. 

It has been estimated that unidentified species could account for around 80% of species. We are currently thought to only know about 1.6 million species, with around 18,000 previously unidentified ones being added to our catalogue of life annually.

There is evidence, however, that some species are becoming extinct before they are even discovered, which could mean estimates of global extinction rates are likely to be too low. Species are already being lost at an unprecedented rate due to human activities that are causing land and coastal use change, pollution, over-exploitation, introduction of foreign species and climate change. In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services warned that about 1 million species of plants and animals are now threatened with extinction. 

The loss of a species from a habitat also has wider implications. Species rely upon each other in interconnected webs known as ecosystems. When one species dies out, it can have a knock-on effect on the others within the same ecosystem. This can be as simple as meaning a loss of an important food source or result in the loss of more complex interactions that are important for a habitat. The loss of a keystone species like a large herbivore from forest or woodland, for example, can change the dynamics of a forest. Diminishing numbers of insects can leave habitats with fewer important pollinators and reduce the recycling of nutrients.