How the ‘evil twin' of the climate crisis is threatening our oceans

Yahoo

09-06-2025

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 about six miles 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 pleasantly calm May morning, Prof James Fishwick, PML's head of marine technology and autonomy, is on top of the buoy checking it for weather and other damage. 'This particular buoy is one of the most sophisticated in the world,' he says as he climbs the ladder 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 – and it is doing so 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 on Monday 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?
It's difficult to see the biological effects because they're going to take a long time to happen
Prof Steve Widdicombe, PML
'It's tough because there is no real smoking gun,' says Prof Steve Widdicombe, director of science at PML and a leading global voice on ocean acidification. 'It's difficult to see the biological effects because they're going to take a long time to happen and differentiating the impacts of ocean acidification from things like temperature, fishing pressures and pollution makes it really hard to generate impetus and momentum in decision-makers and policymakers to really tackle it hard.'
For anyone who wants an immediate idea of its impact, there is a very effective video from the Noaa that shows a pteropod swimming in water with a normal pH level, alongside one where the pteropod has been subject to elevated CO2 levels for two weeks. In the first video the marine creature has a clear shell and is actively swimming, in the second it shows a partially dissolved and fissured shell and the pterapod having difficulty moving in the water. Images such as this help scientists raise awareness of the issue, but on their own they will never be enough.
This lack of visibility and understanding of the impacts of acidification has led scientists to focus on building a body of work that clearly shows the statistical correlations between increasing levels of acidity in the oceans and the changes in biological processes to flora and fauna in the sea in different areas around the world.
A good example can be seen in the north-west of the US. In about 2010, the oyster farming industry there – worth millions of dollars – nearly collapsed after oyster production seemed to drop off a cliff.
Prof Helen Findlay from PML explains the science of what was going on: 'On the west coast you get an upwelling of deep waters, and that deep water has naturally got more CO2 in it. But on top of that, you have the acidification effect from the atmosphere, and that amplified the upwelling effect. It turned out, after some investigation, that the intake pipes connected to the hatcheries were bringing in this acidified water, which had been amplified over the years.'
The level of acidity in the water had reached a point that meant the oysters were trapped in their larval state and unable to grow the shells they needed to develop. The hatcheries then installed sensors to measure the pH of the water and added chemicals to hatchery tanks to neutralise the water when necessary.
Scientists hope that education about initiatives such as in the oyster hatcheries of the north-west US, combined with government funding, will help encourage other countries to take action suited to their particular acidification problem. But large parts of the world do not have access to the information they need to begin planning what to do.
There are obligations for countries to tackle ocean acidification enshrined in international agreements including, most recently, the Global Biodiversity Framework, that aims to halt and reverse biodiversity loss. However, while decision-makers either lack the resources to tackle the issue, or simply twiddle their thumbs over implementing a plan, commercial operators are stepping in to offer alternative solutions.
Geoengineering the ocean is becoming big business. Companies are focusing on different human-made ways to remove carbon from the seas, with perhaps the most developed of these being ocean alkalinity enhancement. This is where an alkaline solution is added to seawater to raise the pH level. Done at a controlled, very local level, such as in the tanks in the oyster hatcheries, this can be effective. But many scientists are concerned that the ocean geoengineering industry is growing far too rapidly.
At the end of the day, CO2 is going up, pH is going down, and that's an urgent issue people are not talking about
Jessie Turner, Ocean Acidification Alliance
'We shouldn't proceed further along this road without the evidence,' says Widdicombe. 'Can you imagine going to your doctor and they say 'I've got a drug here that will fix you.' If the doctor then says we haven't really tested it and we're not sure about the side effects, would you still be happy to take it?'
Jessie Turner, executive director of the Ocean Acidification Alliance, worries that geoengineering may also cause people to lose sight of the obvious. 'While exploring a research agenda around geoengineering interventions is important, the number one manmade solution to ocean acidification is reducing our CO2 emissions,' she says. 'I hope that we're not losing the urgency for that. Without governments paying more attention to ocean acidification, there is this opportunity for the private sector to steer the course.'
Related: Carbon released by bottom trawling 'too big to ignore', says study
Aside from the primary objective of reducing CO2, there are other things that can be done to tackle ocean acidification, including limiting organic pollution in the water, often relatively easy to do at a local level, and creating more resilient marine habitats around our shores.
It is clear, however, that scientists working in this field are getting increasingly frustrated with the lack of urgency around it. Many are hoping that this week's UN ocean conference in France will provide a vital opportunity to discuss the problem with heads of state and get it more firmly on government agendas.
'At the end of the day, we know CO2 is going up, pH is going down, and that's an urgent issue that people are not talking about,' says Turner. 'It's an overlooked consequence of carbon in our ocean that governments can no longer afford to overlook in mainstream policy agendas, and the time to address it is running out.'