Why the possibility of thousands of species going extinct is alarming

Five mass extinction events, including the death of the dinosaurs, shaped the history of Earth and the sixth has been happening for the last 10,000 years, rapidly removing animals from our planet. Scientists define a mass extinction as around three-quarters of all species dying out over a short geological time, which is anything less than 2.8mn years. Since 1970, the populations of vertebrate species have declined by an average of 68%, and currently more than 35,000 species are considered to be threatened with extinction, according to the International Union for Conservation of Nature (IUCN). During the 20th century alone, as many as 543 land vertebrates became extinct. Now, a new scientific study predicts that between 6% and 10% of animal species will be lost by 2050, and between 13% and 27% extinct by 2100, depending on the outcome of different plausible climate change scenarios.
Species extinction is not a new concern, with the IUCN red list finding that over 28% of examined flora and fauna species – more than 42,100 in total – are in danger of extinction. The latest study published in ‘Science Advances,’ is groundbreaking in its use of modelling technology, mapping out the intricate food webs and impacts on local species under different climate change-related conditions. The scientists modelled hundreds of earth simulations populated by over 33,000 species. The article found that the biggest cause of species extinction was climate change (at around 62%), followed by secondary extinctions (20%), local extinction due to competition from invasive species (14%), and land-use change (4%). Quantifying secondary extinctions in this way – for example, when a predator goes extinct because its prey food source has disappeared – is a turning point in measuring the holistic impact of climate change on Earth’s fauna.
“Think of a predatory species that loses its prey to climate change,” says study co-author Professor Corey Bradshaw of Flinders University in a statement. “The loss of the prey species is a ‘primary extinction’ because it succumbed directly to a disturbance. But with nothing to eat, its predator will also go extinct, a co-extinction,” Prof Bradshaw continues.
Until now, researchers have not been able to interconnect species on a global scale in order to work out how much additional loss will take place through co-extinctions. While earlier studies have examined different aspects of extinctions such as the direct effects of climate change and the loss of habitats on species fates, these have not been combined to predict the scale of extinctions. For the latest study, academics used one of Europe’s most powerful supercomputers to make ‘synthetic Earths’ complete with virtual species and more than 15,000 food webs.
The networks were linked by who eats whom and then climate and land use changes applied to the system in order to inform future projections. Virtual species were able to recolonise regions as the climate changed, adapt to changing conditions, go extinct because of global heating, or fall victim to an extinction cascade. Study co-author Dr Giovanni Strona from the University of Helsinki, said: “By running many simulations over three main scenarios of climate until 2050 and 2100 — the so-called Shared Socioeconomic Pathways from the Intergovernmental Panel on Climate Change, we show that there will be up to 34% more co-extinctions overall by 2100 than are predicted from direct effects alone.”
Prof Bradshaw says what is even more frightening is that co-extinctions will raise the overall extinction rate of the most vulnerable species by up to 184% by the end of the century, according to the new projections. “Children born today who live into their 70s can expect to witness the disappearance of literally thousands of plant and animal species, from the tiny orchids and the smallest insects, to iconic animals such as the elephant and the koala ... all in one human lifetime. Without major changes in human society, we stand to lose much of what sustains life on our planet,” the team concludes.