The plastic in the ocean keeps increasing. We're looking at a problem that gets worse every year.
Beneath the surface of every ocean on Earth, microscopic algae have long performed one of the planet's most essential and unheralded services — drawing down the carbon dioxide that human civilization exhales. Researchers at Norway's NTNU have now quantified a quiet disruption to this process: microplastics, accumulating in the sunlit upper waters, are impairing phytoplankton growth through toxicity, light-blocking, and cellular stress, with tropical and arid regions — the ocean's most productive carbon zones — bearing the greatest burden. The loss, currently measured in tens of thousands of tonnes of carbon absorption per year, is modest against the ocean's vast capacity, but the trajectory is not: plastic concentrations are rising, and with them, the slow unraveling of a climate service the world has long taken for granted.
- Microplastics are now so pervasive — from coastal waters to the poles — that they are measurably interfering with the phytoplankton responsible for nearly half of all photosynthesis on Earth.
- The damage operates on multiple fronts simultaneously: certain plastics poison algae directly, others starve them of sunlight, and still others trigger oxidative stress at the cellular level.
- Tropical and arid ocean regions face a disproportionate threat — the very zones with the highest carbon-absorption capacity are proving most sensitive to microplastic contamination.
- For the first time, scientists have folded microplastics' impact on ocean carbon uptake into a formal life cycle assessment, giving policymakers a tool to see plastic's environmental cost across climate, pollution, and biodiversity at once.
- Researchers warn that current losses — between 25,000 and 48,000 tonnes of carbon uptake annually in vulnerable regions — are less alarming than the direction of travel, as plastic entering the ocean shows no sign of slowing.
The ocean absorbs roughly a quarter of the carbon dioxide humans release each year, a service so reliable it has become invisible — until something begins to break it. Researchers at Norway's NTNU have now found that microplastics, the fragmented remnants of consumer goods drifting through every ocean on Earth, are quietly undermining this capacity by interfering with the phytoplankton that drive nearly half of all planetary photosynthesis.
Led by researcher Francesca Verones, the team identified several mechanisms of harm. Some plastics, such as PVC, are directly toxic to algae. Others block sunlight from reaching deeper waters, starving phytoplankton of the energy they need to grow. Still others induce oxidative stress — a form of cellular damage — in the organisms themselves. By combining global phytoplankton data with laboratory measurements, the researchers calculated how rising microplastic concentrations would affect algal growth across different climate zones.
The geography of vulnerability is striking. Tropical and arid regions, which represent the ocean's most productive carbon-absorption zones, are also the most sensitive to microplastic damage. In these areas, the study estimates annual carbon uptake losses of between 25,000 and 48,000 tonnes. Against the ocean's total absorption of roughly two billion tonnes per year, this remains a fraction — but Verones stresses that the trajectory matters more than the current figure, as plastic concentrations continue to rise.
The study is the first to quantify microplastics' effect on ocean carbon uptake within a life cycle assessment framework, part of a broader EU-funded project examining plastic's harm across biodiversity, invasive species spread, and ecosystem services. Verones situates the work within the United Nations' concept of the triple planetary crisis — climate change, pollution, and biodiversity loss — arguing that these challenges are too deeply intertwined to be addressed in isolation. The ocean's carbon-absorbing role, its function as habitat, and its place in the food web are threads in the same living fabric, and as microplastics accumulate, that fabric frays in ways science is only beginning to measure.
The ocean absorbs roughly a quarter of the carbon dioxide humans pump into the atmosphere each year—a service so fundamental that we rarely think about it until something threatens to break it. Now, researchers at Norway's NTNU have found that microplastics, those ubiquitous fragments of broken-down consumer goods drifting through every ocean on Earth, may be quietly undermining this capacity.
The mechanism is deceptively simple. Nearly half of all photosynthesis on the planet happens in the ocean, driven by phytoplankton—microscopic single-celled algae that float in the sunlit upper waters and convert carbon dioxide, water, and sunlight into oxygen and the sugars that build new cells. When these organisms thrive, they pull carbon from the atmosphere and lock it away in the deep ocean, a process that has been one of Earth's most reliable climate regulators. But microplastics, now found everywhere from coastal cities to the Arctic and Antarctic, are interfering with this process in multiple ways.
Francesca Verones, a researcher leading the investigation, explains that the problem operates on several fronts. Some plastics, like PVC, are toxic to the algae directly. Others block sunlight from penetrating deeper into the water column, starving the organisms of the energy they need to grow. Still others trigger oxidative stress—a kind of cellular damage—in the algae themselves. The researchers collected phytoplankton data from different climate zones worldwide and used laboratory measurements to calculate how various concentrations of microplastics would affect algal growth globally.
The findings reveal a troubling geography of vulnerability. Tropical and arid regions, which happen to be the ocean's most productive carbon-absorption zones, are also the most sensitive to microplastic damage. In these areas alone, the study found that microplastics could reduce annual carbon uptake by between 25,000 and 48,000 tonnes per year. To put that in perspective, the ocean absorbs roughly two billion tonnes of carbon annually, so these losses represent a fraction of the total. But Verones emphasizes the trajectory matters more than the current snapshot. The amount of plastic entering the ocean is rising steadily, and as concentrations climb, so will the damage.
This research marks the first time scientists have quantified microplastics' effect on ocean carbon uptake and folded it into a life cycle assessment—a comprehensive accounting method that tracks a product's environmental impact from manufacture through disposal. The broader EU-funded project of which this study is part examines plastic's effects across three dimensions: how it harms biodiversity through entanglement and ingestion, how it spreads invasive species by serving as a vehicle for organisms traveling between oceans, and how it degrades ecosystem services like carbon absorption.
Verones frames the work within what the United Nations calls the triple planetary crisis: climate change, pollution, and biodiversity loss. These three challenges are deeply interconnected, and addressing one in isolation while ignoring the others will not solve the underlying problem. Life cycle assessments, she argues, are among the few tools capable of examining all three simultaneously, making them essential for understanding how human-made materials ripple through natural systems. The ocean's carbon-absorption capacity is not separate from its role as a habitat or a food source; it is woven into the same living fabric. As microplastics accumulate, they fray that fabric in ways we are only beginning to measure.
Citações Notáveis
The ocean plays a crucial role in absorbing carbon from the atmosphere. What happens if marine microplastics affect the plankton?— Francesca Verones, NTNU researcher
Life cycle assessments are one of the few methodologies capable of covering all aspects of what the UN calls the triple planetary crisis—climate change, pollution, and loss of biodiversity.— Francesca Verones
A Conversa do Hearth Outra perspectiva sobre a história
Why does it matter that tropical and arid regions are hit hardest? Aren't all carbon losses equal?
Not quite. Those regions already absorb the most carbon, so they're doing the heaviest lifting in the climate system. Damage there has outsized consequences. It's like losing the strongest worker on a team.
But the study says 25,000 to 48,000 tonnes sounds large until you compare it to two billion. Why should we care about such a small percentage?
Because the percentage is small *now*. The plastic in the ocean keeps increasing. We're not looking at a stable problem—we're looking at one that gets worse every year as more waste breaks down into microplastics.
So this is really about trajectory, not the current damage?
Exactly. The study is a warning about where we're headed, not just where we are. It's the first time anyone has measured this particular harm, which means we've been blind to it until now.
What does a life cycle assessment actually tell us that other studies don't?
It connects the dots. It shows that the plastic bottle you throw away doesn't just become litter—it eventually fragments, travels to the ocean, poisons algae, and reduces the ocean's ability to absorb the carbon from the factory that made the bottle. Everything is linked.
And that's the triple crisis idea—climate, pollution, and nature loss are really one problem?
Yes. You can't solve climate change by ignoring pollution, and you can't protect nature while the ocean's carbon-absorption engine is failing. They're symptoms of the same disease.