Scientists urge caution on Marine Carbon Dioxide Removal as pressure to limit global warming intensifies  

As we live through another year of record temperatures, and as the urgency to address climate change intensifies, interest in technologies designed to enhance the Ocean’s ability to sequester and store carbon dioxide – known as marine carbon dioxide removal (mCDR) – is surging. Yet, these approaches remain shrouded in uncertainty, particularly regarding their efficacy and potential negative impacts on nature and people. 

To help navigate this complex and emerging issue, last week, the Ocean & Climate Platform published the Policy Brief ‘Navigating Hopes and Threats: How Precaution Should Guide Marine Carbon Dioxide Research and Governance’ – built on its latest scientific publications, alongside months of collaborative work with its members and Scientific Committee, including PML’s Professor Helen Findlay.  

The central message is clear: at present, mCDR remains unproven as a scalable solution to mitigate climate change. The priority must remain the urgent – and drastic – reduction of greenhouse gas emissions.  

Relying on the promise of mCDR as a “fix” for removing emissions and to limit warming could create a moral hazard, the brief says, undermining decarbonisation efforts by drawing political attention and financial resources away from proven, ready-to-implement solutions. 

Professor Findlay, who is a Biological Oceanographer at PML, and a leading expert in the consequences of carbon emissions – from global warming to ocean acidification – states the Ocean’s role as a carbon sink is already under a huge strain.   

“The Ocean already plays a critical role in absorbing carbon from the atmosphere – around a quarter of human emissions each year. It is this natural ability to take up and store carbon, which makes the ocean an interesting option for exploring mCDR approaches.” 

“The Ocean is doing its very best to help us, but this has come at a cost.” 

“The Ocean is actually losing its capacity to store carbon as a result of rising temperatures, warming seas, and acidification – all driven by emissions.”   

The Policy Brief reflects a commitment to a precautionary approach to mCDR, grounded in scientific integrity, environmental protection, and social equity – and elaborates a set of recommendations for decision-makers to enable safe and equitable research while preventing any premature deployment. 

The Policy Brief does not argue against marine carbon dioxide removal research. Instead, it calls for carefully governed research to continue – including laboratory studies and responsibly conducted field trials – ensuring that any future decisions are informed by robust scientific evidence. Its recommendations aim to support safe, equitable research while preventing premature large-scale deployment. 

Professor Findlay explains: 

“We can’t answer the important questions about marine carbon dioxide removal without doing the research.” 

“If these approaches are ever going to play a role alongside rapid emissions reductions, we need independent, ethical and transparent science to understand both their potential and their risks.” 

“That means investing in carefully designed laboratory studies, field trials and larger-scale research that are conducted responsibly and with strong environmental safeguards. The evidence we gather now will help ensure that any future decisions are based on science, rather than hope or speculation.” 

Access the Policy Brief: ‘Navigating Hopes and Threats: How Precaution Should Guide Marine Carbon Dioxide Removal Research and Governance’ >> 

Why is marine carbon removal attracting so much attention? And how much CO₂ do we need to limit global warming to 1.5C°? What will happen if we don’t limit warming to 1.5C°?  

We break down the science to make the issue accessible to all below… 

How much CO₂ must we remove to limit global warming to 1.5C°?  

Though invisible, greenhouse gases have measurable mass – and amount to billions of tonnes in the atmosphere.  

To meet the Paris Agreement and keep global warming below 1.5°C, CO2 removal needs to happen alongside emissions reductions – scientists estimate that between 7 and 9 gigatonnes of CO₂ will need to be removed from the atmosphere every year by 2050. A gigatonne is one billion metric tonnes.  

Yet current global carbon removal capacity is only around 2 gigatonnes annually – the vast majority coming from traditional land-based approaches such as tree planting, which draw down CO₂ through photosynthesis.  

What will happen if we don’t limit warming to 1.5C°?  

Failing to limit warming to 1.5°C could have profound and irreversible consequences. Recent research involving PML’s Professor Helen Findlay highlights how exceeding this threshold would accelerate global ice loss, driving metres of sea-level rise that could be observed in our lifetime – putting coastal communities at risk worldwide. Melting ice sheets and warming oceans are also expected to disrupt major ocean currents, with far-reaching impacts on climate systems and more frequent extreme weather events.   

At the same time, increasing carbon emissions will worsen ocean acidification – which was found to have crossed its Planetary Boundary in a landmark study led by Prof Findlay last year – which threatens key marine species and entire food webs.  

These findings reinforce both the urgency of deep emissions reductions and the need to consider additional carbon removal strategies alongside them – and so marine carbon dioxide removal has gained considerable interest in recent years. 

PML’s research on mCDR: 

Just last year, Prof Findlay co-authored the first comprehensive study investigating the impacts of Direct Ocean Carbon Capture and Storage (DOCCS) discharge on marine ecosystems – which found that the release of treated, high pH seawater could place stress on certain marine organisms, especially those near to the discharge site.  

Marine carbon dioxide removal approaches like these work by electrochemically removing dissolved inorganic carbon from seawater, which can then be stored. The treated, low-carbon, high pH seawater is released back into the ocean, where it naturally draws down more atmospheric CO₂, gradually returning the seawater to normal pH and carbon levels.  

This type of mCDR research has further been trialed by Plymouth Marine Laboratory through the SeaCURE project – the UK’s first mCDR pilot facility of its kind – to test the effectiveness of this mCDR approach in real world conditions, but at a small scale, and following the principles outlined in the statement. 

Further information: 

PML backs call for safeguards on emerging ocean carbon removal technologies 

PML Scientists Share Evidence on Marine Carbon Dioxide Removal in Westminster   

Harnessing decades of ocean acidification research to shape marine carbon removal solutions