The 'evil twin' of climate crisis Scientists warn about ocean acidification

Researchers call for action on marine life amid fears that falling pH levels and buildup of CO2 in seas are not being taken seriously enough

- By Lisa Bachelor

On a clear day at Plymouth marina you can see across the harbour out past Drake's Island - named after the city's most famous son, Francis Drake - to the Channel.

It's quite often possible to see an abundance of marine vessels, from navy ships and passenger ferries to small fishing boats and yachts. What you might not spot from this distance is a large yellow buoy bobbing up and down in the water 10km off the coast.

This data buoy - L4 - is one of a number belonging to Plymouth Marine Laboratory (PML), a research centre in Devon dedicated to marine science.

On a calm May morning, Prof James Fishwick, PML's head of marine technology and autonomy, was on top of the buoy checking it for damage. "This buoy is one of the most sophisticated in the world," he said as he climbed to the top. "It's decked out with instruments and sensors able to measure everything from temperature, to salinity, dissolved oxygen, light and acidity levels."

It's the hourly recordings of this last measurement, the pH of the water, that are adding to a picture locally and globally that is increasingly concerning scientists. The results show that ocean acidification is rising - at an alarming rate. Ocean acidification, often called the "evil twin" of the climate crisis, is caused when carbon dioxide is rapidly absorbed into the ocean, where it then reacts with water molecules, leading to a fall in the pH of the seawater.

A paper out this week from scientists at PML, the US-based National Oceanic and Atmospheric Administration (Noaa) and Cimers (Oregon State University), shows ocean acidification is happening more rapidly than previously thought.

Part of the problem for scientists in bringing it to the world's attention is that you can't see the pH levels in the sea at the beach near you, so how do you know it is happening?