The Ocean Is Fighting Climate Change: How People Are Trying to Help It

We replaced the stove with plywood, turning the kitchen of the dive boat into an impromptu research lab. Plugging in wires and connecting tubing, we assembled a scientific instrument within the cramped cabin. Then we cast off into Halifax Harbor, Canada, surveying the turquoise waters for signs of an unusual test: could we use the ocean itself to remove carbon dioxide from the air?

Carbon dioxide (CO₂) is the most important driver of climate change, but it cannot be seen. Its build-up in the atmosphere is gradual. Its worst consequences take time to emerge. Even if emissions fell sharply tomorrow, the CO₂ already released would continue to warm the planet.

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That is why scientists and policymakers are increasingly turning to carbon dioxide removal (CDR): taking CO₂ that has already been released back out of the air. So far, most large-scale CDR has focused on land, such as reforestation. But land is finite, competes with food production and biodiversity, and stored carbon can be lost through fire or deforestation. As emissions continue to outpace what these approaches alone can manage, attention has turned toward the ocean.

The Overlooked Role of the Ocean in Carbon Storage

The ocean covers about 70% of Earth's surface and holds roughly 50 times the amount of carbon found in the atmosphere. Before the industrial revolution, carbon moved between air and sea in near balance. As industrial activity increased atmospheric CO₂, more of it dissolved into seawater and the ocean became more acidic.

All that dissolved carbon has resulted in the ocean storing about a third of human CO₂ emissions since the industrial revolution—substantially slowing the pace of climate change. The emerging question is whether we can build on this natural service. The field exploring that possibility is known as marine carbon dioxide removal (mCDR).

All mCDR approaches aim to reduce the amount of dissolved CO₂ at the ocean surface, converting it into more stable forms. When surface CO₂ is reduced, more CO₂ from the atmosphere dissolves into the sea.

Reducing Surface CO₂—so the Sea Absorbs More

One approach involves adding alkaline minerals—often crushed or processed rocks like limestone or basalt—to seawater. This reduces acidity and increases the capacity of seawater to absorb more carbon and store it for centuries to come.

This is the strategy under development by Planetary Technologies in Halifax Harbor, Canada. There, alkaline minerals have been introduced to seawater through the cooling water discharge pipe of a natural gas burning power plant.

Another approach relies on biology. The ocean is filled with microscopic organisms that photosynthesize, using dissolved CO₂ to grow and reproduce. Some of this carbon sinks into deeper waters, through a process known as the "biological carbon pump." By adding the nutrients that these organisms need to thrive, this effort hopes to increase microorganism populations and, ultimately, strengthening the biological carbon pump.

How Do We Know It Works?

Whether chemical or biological, these approaches face the same questions: how much additional CO₂ is actually being removed from the atmosphere? And what are the ecological consequences?

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The processes involved are invisible to the naked eye. The organisms are microscopic. The carbon transformations are chemical. Yet if marine carbon removal is to scale to climate-relevant levels, it will require rigorous measurement, transparency and public trust.

In the Cassar Lab at Duke University, we develop instruments to detect subtle changes in seawater chemistry. They continuously measure dissolved gases and other tracers, allowing us to reconstruct what microorganisms are doing and how carbon is moving through the system.

In August 2025, we deployed one of these tools in the turbulent waters surrounding one of the world's first coastal ocean alkalinity enhancement projects, off Nova Scotia, Canada. This instrument was a mass spectrometer that extracts and quantifies dissolved gases from seawater.

These readings give us insight into the ecosystem's balance between photosynthesis and respiration—and therein, an understanding of how stressed or healthy the surrounding ecosystem is. Working alongside researchers tracking the chemical changes of the mCDR work underway, we focused on understanding how marine microorganisms were responding.

Another instrument, known as the Gopticas, allows a precise quantification of how much photosynthesis is happening in a seawater sample. The Gopticas was recently exhibited Prototypes for Humanity, an international innovation initiative based in Dubai, highlighting how tools developed for fundamental oceanography can also underpin climate accountability. This allows stronger quantification of ecosystem health as well as carbon influx.

A Scalable Approach to mCDR Monitoring

We are now forming a team that can deploy these tools to directly quantify the amount of CO₂ being converted into longer-lived forms—and to spot early signs of ecological disruption.

This kind of monitoring is crucial. It allows us to distinguish between carbon that is briefly cycled near the surface and carbon converted into forms likely to remain stored for centuries.

It also provides early warning if an intervention begins to disrupt marine biology. The work in Halifax marked the first application of our instruments to mCDR initiatives, but we look forward to applying these same approaches across regions and mCDR approaches.

Developing robust methods to quantify both carbon removal and ecological impact before large-scale deployment is essential. Without credible verification, claims of carbon removal risk outpacing evidence. And without clear evidence of environmental safety, public support will falter.

If marine carbon dioxide removal is to make a meaningful contribution to climate mitigation, it must rest on precise measurement and accountability. Governments, regulators and investors will need confidence that reported carbon removal is real and durable—and that marine ecosystems are protected.

Standing on the deck of the dive boat, staring out at the plume of alkaline waters emerging from the pipe, it's easy to be struck by a feeling of awe. This experiment is tiny compared to global climate change—a drop in the ocean. But it offers a glimpse into a more optimistic future.