Earth is seeing an unprecedented loss of species, which ecologists are calling a sixth mass extinction. Almost all past extinctions have occurred by natural processes, but today human activities are overwhelmingly the main cause of extinction.
There is no doubt that biodiversity loss, together with climate change, are some of the biggest challenges faced by humanity. Along with human-driven habitat destruction, the effects of climate change are expected to be particularly severe on biodiversity. Current estimates of extinctions are, without a doubt, gross underestimates.
The Earth's fossil record shows that the average lifespan of a species is between 1 and 10 million years. Of all the species that ever lived on Earth, 99.9 percent are now extinct. So whilst extinction is a natural phenomenon, extinction rates of hundreds or even thousands of times background rate have occurred and qualify as mass extinctions. In events such as these it is apparent that the demise of species is hastened by major changes to the planet. The causes and effects of these changes included numerous impacts by asteroids and comets which produced huge dust clouds, oscillating climatic extremes, major changes in sea level, and prolonged periods of volcanism caused by tectonic movements of the Earth's plates.
The number of species on Earth is currently estimated to be anywhere between 7 and 50 million, probably around 30 million species. Only about 1.4 million have been named and briefly described. Guessing the pace of extinction is therefore complicated, but estimations show a natural rate of around one species a year. The present human-caused rate is hundreds of times higher, resulting perhaps in the extinction of four species every hour. About one-quarter of the earth's species risk extinction within the next thirty years. The tropical deforestation alone will wipe out 5-15% of all species between 1990 and 2020.
Trends documented by the the World Bank and Worldwatch Institute, and reported to the Rio+5 conference in 1997, estimated 150 to 200 species of life become extinct every 24 hours.
In May 2019, a United Nations report warned that 1 million species are threatened by extinction. More recently, 571 plant species were declared extinct. Some plants have been going extinct up to 350 times faster than the historical average – with devastating consequences for unique species. Based purely on numbers, biodiversity hotspots, like Madagascar, are expected to lose more species to extinction than coldspots, like the UK; however, coldspots stand to lose more uniqueness than hotspots, for example, seven coldspot extinctions led to the disappearance of seven genera, and in one instance, even a whole plant family.
Botanists at an International meeting in St Louis, USA in 1998 warned that two thirds of all species of mammals, birds, butterflies and plants will disappear by the end of the next century due to the destructive habits of man. They claim that the current rate is similar to the mass extinctions that wiped out the dinosaurs 65 million years ago. The destruction is piecemeal as humans encroach on the natural environment and fragment it, leaving little room for other species to survive.
Key areas of concern are: wild relatives of domesticated species which are essential to maintain the genetic variety of the domesticated breeds; harvested species and the threat to them through unsustainable rates of harvesting, leading to their biological extinction; totemic species, namely those held to be of special socio-cultural value to particular peoples; species of special importance to science; animal species that are sufficiently important and endangered to warrant captive breeding (especially in the light of the limited facilities for such breeding); wide-ranging species that move between non-contiguous ecosystems, because of their ecological value and because an exclusively ecosystem-oriented approach will not conserve them; and indicator species because of their role in indicating the effectiveness of ecosystem maintenance.