Scientists say it will take millions of years to undo the damage humanity is currently causing on the world’s biodiversity, described as a 6^th mass extinction. A new study found that the rate of biodiversity decline in freshwater ecosystems outcompetes that during the end-Cretaceous mass extinction event, which wiped out the dinosaurs.

Biodiversity in freshwater ecosystems is disproportionally high. Although they cover only 1% of the Earth’s surface, these ecosystems account for about 10% of the global species richness. But these environments are currently experiencing a massive deterioration, with an alarming decline in regional species richness and individual abundance.

This biodiversity crisis is widely considered the onset of a major extinction event, the so-called 6th mass extinction. It resembles in several aspects the 5th mass extinction at the Cretaceous–Paleogene boundary 66 million years ago, caused by an asteroid impact. Globally 76% of all species are estimated to have gone extinct back then.

An international group of evolutionary biologists, paleontologists and geologists compared the previous crisis to the current one, driven by human activities and greenhouse gas emissions. Focusing on freshwater biota, they gathered a dataset with 3,387 fossil and living snail species of Europe covering the past 200 million years.

The scientists estimated rates of speciation and extinction to assess the rate at which species come and go, as well as to predict recovery times.

The results of the study are alarming. While the extinction rate during the 5^th mass extinction was higher for freshwater ecosystems compared to other ancient ecosystems, it’s overshadowed by the predicted future extinction rates.

The researchers found that the predicted rate of the 6^th mass extinction was three orders of magnitudes higher than during the time the dinosaurs went extinct. By 2120, a third of the living freshwater species may vanish from the planet. We are losing species at an unprecedented rate that hasn’t been reached any time in the past.

“Losing species entails changes in species communities and, in the long run, this affects entire ecosystems. We rely on functioning freshwater environments to sustain human health, nutrition and fresh water supply”, Dr. Thomas A. Neubauer, the lead author of the study, said in a statement. 

Despite the 5^th mass extinction was a short event in geological time scales, the extinction rate remained high for approximately five million years. Afterwards followed an even longer period of recovery of 12 million years. The researchers think that’s how much time we need now, even if the impact on the world’s biota stops today. 

Neubauer said that the effects of the biodiversity crisis will continue for an “extended period of time.” It’s all happening much faster than in previous extinction events and it will require a longer recovery period. “Despite our short existence on Earth, we have assured that the effects of our actions will outlast us by millions of years,” he added. 

Meanwhile, action to stop the biodiversity crisis is so far lacking. A UN report showed last year that world leaders have failed to meet a set of important biodiversity goals known as the Aichi targets – the equivalent to the Paris Agreement on climate change. New targets are currently being negotiated and should be agreed upon later this year. 

The study was published in the journal Communications Earth & Environment.