If biodiversity continues to decline in freshwater environments at the current rate – which is higher than the extinction event that killed off the dinosaurs – the damage may take millions of years to overcome (1).

With hundreds of endangered species and their habitats destroyed due to climate change, pollution and over-exploitation, the current decline in biodiversity is probably the most challenging problem humankind must solve now.

To understand how long it will take to recover from this extinction event, a team of European scientists from Germany, Switzerland, the UK and The Netherlands decided to compare it with the previous mass extinction event, which occurred 66 million years ago when an asteroid hit our planet. This was a major event event that wiped off dinosaurs along with 75% of all species.

Looking at aquatic species – often the most affected – the team collected data from 3,122 fossil and living snails species from the past 200 million years. Freshwater snails are incredibly useful to predict extinction and diversity recovery. They are some of the most diverse species of freshwater animals and have the best-preserved fossil records. In addition, they live in virtually all freshwater habitats worldwide and have many different reproductive strategies.

With this extensive database, the scientists calculated the speed at which species come and go to predict recovery times. Worryingly, while the rate of extinction that killed the dinosaurs – known as the 5th extinction event – was considerably high for freshwater species, it doesn’t even compare with the rate for the current 6th extinction event.  On average, extinction rates are three orders of magnitude higher now than when dinosaurs went extinct. In fact, according to the model, by 2120, a third of all living freshwater species will have perished if current trends are not overturned. “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 freshwater supply”, says the lead author of the study, Dr Thomas A. Neubauer.

The 5th mass extinction event actually shares many features with our current situation, including a steep increase in temperature caused by rising CO2 levels. Sadly, whereas the dinosaur extinction was caused by a fluke of nature that could not have been avoided, our current biodiversity crisis is primarily the result of human impact.

And this is not the most alarming news. The previous extinction event started with an asteroid impact on the Yucatán Peninsula in Mexico. In geological terms, the asteroid hit our planet in the blink of an eye, but extinction rates spread over the following 5 million years. Then it took a further 6 million years to restore the balance, with new species taking the space of the ones that went extinct.

Translating these results to the current crisis, it’s likely that this phase of extinction will continue for several million years, not to mention an extended period for the following recovery stage. Given the extremely fast pace at which global change is happening today, Europe’s freshwater species are facing even more dramatic changes than after the asteroid impact.

“Even if our impact on the world’s biota stops today, the extinction rate will likely stay high for an extended period of time. Considering that the current biodiversity crisis advances much faster than the mass extinction event 66 million years ago, the recovery period may be even longer”, says Neubauer. “Despite our short existence on Earth, we have assured that the effects of our actions will outlast us by millions of years.”

(1) Neubauer, T.A., Hauffe, T., Silvestro, D. et al. Current extinction rate in European freshwater gastropods greatly exceeds that of the late Cretaceous mass extinction.Commun Earth Environ 2, 97 (2021). https://doi.org/10.1038/s43247-021-00167-x