Current rates of ocean acidification are unparalleled in Earth's history

The study, based on an expert workshop led by Columbia University's Lamont-Doherty Earth Observatory and the University of Bristol, assessed in detail a number of climate change events in the planet's history, including the asteroid impact that made the dinosaurs go extinct and the Permian mass-extinction which wiped out around 95 per cent of all life on Earth. The findings are reported this week in Science.

Oceans are currently absorbing about a quarter of the CO₂ released into the atmosphere, lowering the pH of the surface ocean. As atmospheric CO₂ increases, so does the rate at which it will dissolve in seawater, forcing surface ocean pH lower and lower – a process called ocean acidification.

Laboratory experiments suggest that if the pH continues to fall, we may start to see impacts on marine organisms such as slower growth, fewer offspring, muscle wastage, dwarfism, reduced activity and the dissolution of their carbonate shells – with knock-on effects throughout the marine ecosystem. However, as a large number of processes are involved, it is hard to predict what ecosystems in the oceans will look like in future and to what extent humans will be able to continue to benefit from the resources oceans provide.

In order to learn about the future, the researchers looked to the past, reviewing climate events over the past 300 million years that showed evidence of elevated atmospheric CO₂, global warming and ocean acidification.

Dr Daniela Schmidt, a Royal Society Research Fellow in Bristol University's School of Earth Sciences, was one of the organizers of the workshop which gathered all the experts and compiled the evidence. She said: "Laboratory experiments can tell us about how individual marine organisms react, but the geological record is a real time experiment involving the entire ocean."

Professor Andy Ridgwell added: "The geological record suggests that the current acidification is potentially unparalleled in at least the last 300 million years of Earth history, and raises the possibility that we are entering an unknown territory of marine ecosystem change.

"Although similarities exist, nothing in the last 300 million years parallels rates of future projections in terms of the disrupting of ocean carbonate chemistry – a consequence of the unprecedented rapidity of CO₂ release currently taking place."

'The Geological Record of Ocean Acidification' by Bärbel Hönisch, Andy Ridgwell, Daniela N. Schmidt et al. in Science

This work was based on a workshop on Paleocean Acidification and Carbon Cycle Perturbation Events funded by the National Science Foundation (NSF) and PAGES (Past Global Changes).

Professor Ridgwell and Dr Schmidt are funded by the Royal Society in the form of University Research Fellowships