NEW EVIDENCE ON THE SEVERITY OF OCEAN ACIDIFICATION

Study led by the UK’s Plymouth Marine Laboratory, US-based NOAA, & OSU (Oregon State University) finds threat to global marine ecosystems worse than previously thought

“Ocean acidification has been identified in the Planetary Boundary Framework as a planetary process approaching a boundary that could lead to unacceptable environmental change. Using revised estimates of pre-industrial aragonite saturation state, state-of-the-art data-model products, including uncertainties and assessing impact on ecological indicators, we improve upon the ocean acidification planetary boundary assessment and demonstrate that by 2020, the average global ocean conditions had already crossed into the uncertainty range of the ocean acidification boundary.”

-- Ocean Acidification: Another Planetary Body Crossed, Helen Findlay, et al.

Interview with Dr. Helen Findlay, Biological Oceanographer/ Professor Plymouth Marine Laboratory, UK

By Suzanne Forcese

WT: Helen, you have an impressive bio that also includes your work with GlobalOcean Acidification ObservingNetwork(GOA-ON) and lead coordinator for the North East Atlantic Ocean Acidification (NEA-OA) regional hub of GOA-ON. Please introduce yourself to our viewers outlining your area of research, why this is your passion, and your mission.

Findlay: I am a biological oceanographer, who studies how the oceans are changing and what this means for our marine ecosystems. I’ve been working in this field for almost 20 years and have watched the ocean change in that time. I am passionate about science – I was always one of the kids that asked “why?” – and I love the ocean, so this is the perfect career.

I don’t really have a mission, other than to do excellent science and pass on that knowledge and evidence to others so that we can make the most informed decisions by raising public awareness of ocean health and training the next generation of scientists through various educational programs.

WT: Please define for our viewers what "ocean acidification" is -- what causes it, what damage does it create, and how climate change is involved in this process.

Findlay: The ocean naturally takes up carbon dioxide (CO2) from the atmosphere, and it has taken up about 25% of the CO2 emissions resulting from human activity each year.

CO2 when dissolved in seawater, reacts with the water to form a weak acid (carbonic acid) and this becomes part of what we call the marine carbonate system, exchanging from carbonic acid to hydrogen ions and bicarbonate and carbonate ions.

Naturally, the ocean and atmosphere stay in balance, and any changes in CO2 are buffered by geological weathering processes that add more bicarbonate and carbonate ions to the system.

But because we are adding so much CO2, and (importantly) adding it so quickly, these long-term buffer processes aren’t able to keep pace, and so the carbonate chemistry is changing, resulting in the oceans becoming more acidic and losing some of its carbonate ions. This change in chemistry is what we call ocean acidification (OA).

OA is directly linked to climate change because it is a direct chemical reaction with the CO2 that’s taken up into the ocean from the atmosphere. The same CO2 that causes climate change.

WT: Please describe what "planetary boundary" is and how/why this is a boundary that demands attention.

Findlay: The planetary boundary framework is a concept set out by the Potsdam Institute about 15 years ago to define key planetary processes that allow our planet to function and thus create a ‘safe’ space for humanity. ‘Safe’ really meaning the stable period of time that humans have evolved in, that has allowed us to develop the societies that we now operate in, i.e. the Holocene era prior to the industrial revolution.

The boundaries indicate when we move outside of this ‘safe’ space. In other words, move outside of conditions we known have been stable in the earth’s system.

Moving beyond these boundaries moves us into an era of uncertainty in terms of knowing how the planet will function, as it is not conditions, which have existed in before.

There are currently 9 planetary processes. The last report, in 2023, concluded we’d crossed 6 out of the 9. The PBs are a way of communicating complex science in relatively simple messages to the non-scientific community to make decisions about how we manage our impact on the planet.

WT: In the recent paper, “Ocean Acidification: Another Planetary BoundaryCrossed” (published in the journal Global Change Biology, June 9,2025 which coincided with the first day of the UN Ocean Conference in Nice) what conclusions have you and your team drawn? How did you come up with your data?

Findlay: Ocean acidification is one of the 9 boundaries. In 2023, the boundary was considered as not yet crossed. But it was believed to be close.

Our new paper reassessed the current state of OA. We also assessed whether the boundary as it stood was fit for purpose and considered some additional aspects like sub-surface conditions and additional biological indicators.

So, the OA planetary boundary considers more of an environmental perspective, given how much the ocean provides us (in a goods and services sense -- How quickly can we change the ocean chemistry (i.e. ocean acidification) without it impacting marine ecosystems and its associated ecosystem services?

We used the latest data and models that are combined to produce our best estimates of global conditions from the year 1750 to present day. The data is a truly global effort, as the OA community is very open and shares data (knowing how difficult it is to collect oceanographic data, we’re all keen to help each other, and it keeps all the data in check). By compiling large datasets together with the best available models, we can minimize uncertainties.

We found that about 40% of the surface ocean had crossed the boundary, and about 60% of the subsurface ocean had crossed the boundary. We found that there were large reductions in suitable conditions for normal growth and development of the key indicator species we looked at: >60% loss of suitable habitat for polar pteropods, >40% loss of suitable habitat for warm-water corals, and ~10% loss of suitable habitat for coastal shellfish.

WT: Are there regional differences in the amount of ocean acidification?

Findlay: Yes, there absolutely are. And this is another aspect we wanted to include in the new paper, that wasn’t included in the original OA boundary assessment.

The polar regions are seeing the fastest rates of change, with 87% of the Southern Ocean, 84% of the north Pacific, 78% of the Arctic, 63% of the north Atlantic having crossed the boundary.

Interestingly, we found that although the tropical and sub-tropical regions (where the warm-water corals are found) hadn’t significantly crossed the boundary, the boundary was not keeping them ‘safe’ from marginal conditions, and these lower latitude regions had passed beyond the biological threshold for marginal growth conditions.

WT: this is alarming. What is the impact on marine life, vegetation, coastal communities etc.? Please give us some examples in various global regions.

Findlay: All the impacts on our planet that we are causing should together be considered crises. OA is one part of the story.

The fact that we’re now 7 of 9 boundaries crossed should give us some cause for concern!

One of the points we make is that OA isn’t happening in isolation, and so we need to give the system space to be more resilient to these big planetary scale system changes.

For instance, coral reefs – we are all familiar with warming waters and marine heatwaves causing bleaching events. OA is going to start adding to the impact on corals, by eroding away the ‘dead’ coral, which are the foundations of reef structures. It will also make it more energetically costly for coral to recover from bleaching events. So together the two act to make it even harder for coral to thrive.

Without coral reefs, local communities will lose food security. It will impact fishing, tourism, coastal protection.

In other areas, for example the west coast of North America, there are impacts already occurring on the shellfish industry. For about 10-15 years the oyster hatcheries along the coast have experienced increasing acidification events that prevent the oyster larvae from developing successfully. The communities there have had to adapt, by either moving location, or improving their monitoring, or adding alkalinity at certain times to their hatcheries… This type of problem could become more widespread.

WT: Some reports suggest all shellfish are going to die off in the next 5 -10 years. Would you say this is an accurate projection?

Findlay: This isn’t the case. However, more places will start to experience what the west coast of America has experienced for some time. We need to act to minimize further damage, but we also need to look at adaptation. Let’s not just watch this unfolding for another 20 years.

WT: Based on your findings -- what are the recommendations moving forward? How can awareness be raised and action taken?

Findlay: The only sure way of preventing further acidification is to reduce CO2 emissions. This should be our number one priority. Alongside that, we need to give the oceans space to recover and therefore have some resilience to these large global issues that are not quick fixes. For instance, local marine protected areas help remove human pressures. Preventing large nutrient flows into the ocean as run-off from agriculture, can prevent local additional acidification events. Restoring ‘blue carbon’ habitats (such as mangroves, seagrass and kelp forests) can provide some local protection against the impacts of OA.

Awareness can drive change, but only if people see positive results from their action. We need to be telling the good news stories as well as the disaster stories.

 Related:

Ocean Acidification: Another Planetary Boundary Crossed