Past extinctions point to a current and future biodiversity crisis

Rapid climate change is a unifying feature of ancient mass extinctions - how bad might it be now?

At one level extinction normal and natural. Most of the diversity of life on Earth that has ever existed is now gone, and all species will one day pass from being extant to being extinct. But although it is normal for species to die out, the normal rate is considered to be quite low. On average perhaps just one or two species go extinct in any given year out of all of the bewildering diversity of beetles, mammals, plants, microbes, worms, fungi and fish. In short, a tiny percentage of the literally millions of species.

The current rate of loss though, while naturally hard to measure (not least when we have perhaps only described around 20% of the species on Earth) is considered to be considerably higher. There is a growing list of species we know have gone extinct in the last century and plenty of others are critically endangered or already doomed to extinction (some species have no known breeding animals, or are known from populations of only males). Even though many species are still apparently flourishing they are at a fraction of their previous distribution and populations - there may be tens of thousands left in one forest, but if they formerly numbered in the millions and were much more widespread, then they are now clearly very vulnerable to an outbreak of disease or a single disaster like a flood or fire. Naturally then, there is huge concern about what is happening to these species and what it might mean in the future and scientists are keen to show how bad this may be and for people to respond.