Ocean health is entering a critical phase, with human-induced carbon dioxide emissions pushing ocean acidification levels beyond safe limits in vast areas of the marine environment, a recent study reveals. This alarming development underscores the urgent need for enhanced ocean protection and a significant reduction in CO2 emissions, experts emphasize.
The findings, while troubling, are not unexpected, according to Helen Findlay, a biological oceanographer at the Plymouth Marine Laboratory in the UK. She notes that the persistent high levels of carbon dioxide emissions have long been a concern for scientists.
For decades, researchers have understood that CO2 emissions are absorbed by seawater, leading to chemical reactions that release hydrogen ions and reduce carbonate ions. This process, known as ocean acidification, has escalated alongside atmospheric emissions, posing significant threats to calcifying marine species that rely on calcium carbonate for their shells. The potential harm to these species could have cascading effects throughout marine ecosystems.
“We have really good data sets, and the data sets and this paper really just emphasise that we’re just watching the system crash.… [W]e need to be making real change now so that we don’t make things worse,” Findlay says.
Scientific Insights and Global Implications
Johan Rockström, director of the Potsdam Institute for Climate Impact Research in Germany, concurs with the study’s findings, noting that we are moving beyond the safe boundary for ocean acidification. His team, known for their planetary boundary research, is preparing an updated Planetary Health Check, highlighting the urgency of the situation.
Mounting evidence of worsening ocean acidification calls for more ambitious ocean protection and rapid climate action, Rockström asserts. He emphasizes that the additional stressor of ocean acidification strengthens the argument for protecting marine systems already under pressure from multiple stressors.
“For all efforts to protect the ocean, it would be beneficial to stop emissions. The way forward is… to stop CO2 emissions, and then the natural systems over time, over a long time, will help us bring things back into balance,” says Hans-Otto Pörtner, marine biologist at the Alfred Wegener Institute.
Depth of the Crisis: Acidification Beyond the Surface
Findlay’s research indicates that four of seven ocean basins have crossed the planetary boundary for ocean acidification, with polar waters and upwelling areas being particularly affected. Alarmingly, 60% of the world’s oceans have surpassed safe acidification limits down to 200 meters depth, compared to 40% at the surface. This is concerning for marine biodiversity, which thrives in these deeper waters.
The study proposes a stricter safe limit for ocean acidification, suggesting a 10% aragonite saturation threshold to maintain ocean ecosystem integrity. This revised limit indicates that the safe space was crossed as far back as 2000.
The consequences are stark: tropical and subtropical coral reefs have lost 43% of their suitable habitat, polar pteropods have lost 61%, and coastal bivalves have lost 13%. These declines in habitat for calcifying creatures highlight the urgent need for action.
Urgency for Ocean Protection and Policy Action
Globally, marine protection efforts lag behind those on land. However, momentum is building following the 2025 UN Ocean Conference, with new Marine Protected Areas and ocean protection commitments emerging. The High Seas Treaty, aiming to protect 30% of the world’s oceans by 2030, is a crucial step forward, though it requires ratification by more nations to come into force.
Findlay believes her team’s findings should motivate countries to ratify the treaty, emphasizing that additional ocean protection can bolster ecosystem resilience against issues like acidification.
“Any additional protection that’s placed on the ocean, provides an opportunity for ecosystem resilience against harder-to-solve issues, such as [ocean acidification],” she says.
Addressing the Root Cause: Carbon Emissions
Experts agree that the primary solution to ocean acidification is tackling its root cause: carbon emissions. With the window to keep global warming below the 1.5°C Paris Agreement target rapidly closing, urgent action is needed.
Even if CO2 levels were reduced today, the effects of ocean acidification would persist for centuries. Experts advocate for net zero and net negative approaches, including some geoengineering solutions, though these remain in early stages and require careful consideration of potential impacts.
Reducing ocean acidification may involve novel methods like ocean alkalinity enhancement, but these come with uncertainties regarding their effects on marine life. Despite the challenges, experts emphasize the importance of reducing emissions and enhancing ocean protections.
“This doesn’t have to be all doom and gloom in terms of all ocean life … dying,” says Nina Bednarsek, assistant professor at Oregon State University. “This sort of knowledge is absolutely critical. It’s not just… to be alarmist. It’s … so we can do something about this.”
The urgency of addressing ocean acidification and its root causes cannot be overstated. With concerted global efforts, there is hope for reversing the damage and ensuring a sustainable future for our oceans.
