Microplastics are reducing the capacity of oceans to absorb carbon dioxide, weakening one of the planet’s most critical natural defences against the climate crisis, a new study warns.
Researchers found the spread of microplastics through marine ecosystems was interfering with the processes that allowed oceans to store carbon and regulate temperature.
Oceans are the planet’s largest carbon sink and “microplastics are undermining this natural shield against climate change”, Ihsanullah Obaidullah from the University of Sharjah, one of the study’s authors, said. “Tackling plastic pollution is now part of the fight against global warming.”
Microplastics, particles smaller than five millimetres across, have made their way into every nook of the planet, from deep ocean waters and Arctic ice to soil, air and even human bodies. While they are widely recognised as a major pollution problem, their role in the climate crisis has received much less attention, according to researchers.
“Climate disruption and plastic pollution are two major environmental challenges that intersect in complex ways,” they explained. “Microplastics influence biogeochemical processes, disrupt oceanic carbon pumps and contribute directly to greenhouse gas emissions.”
Oceans absorb about a quarter of the carbon dioxide released by human activity every year, slowing the pace of global warming. A major part of that process is the “biological carbon pump”, in which sea phytoplankton absorb carbon through photosynthesis and transfer it to deeper ocean layers when they die or are eaten.
The study published in the Journal of Hazardous Materials warns that microplastics interfere with this system by reducing phytoplankton photosynthesis and impairing the metabolism of zooplankton, both of which play a central role in carbon cycling.
“In marine ecosystems, MPs alter the natural carbon sequestration by affecting phytoplankton and zooplankton, which are key agents of carbon cycling,” it said.
Researchers also highlight the role of the “plastisphere”, the communities of microbes which colonise plastic particles in the ocean. These microbes can influence carbon and nitrogen cycles and contribute to greenhouse gas production.
Dr Obaidullah warned that the effects could intensify over time. “Microplastics disrupt marine life, weaken the biological carbon pump, and even release greenhouse gases as they degrade,” he said.
“Over time, these changes could lead to ocean warming, acidification, and biodiversity loss, threatening food security and coastal communities worldwide.”
Rather than presenting new field experiments, the authors analysed existing scientific literature to map how microplastics interacted with ocean health and climate systems, and to identify gaps in current understanding.
“The extent to which microplastics affect climate change, ocean health, and associated systems is currently unknown,” they wrote. “The significant ecological effects of plastic pollution in the oceans are well recognised but its exact connections to these extensive environmental processes are not well understood.”
While the study warns that the persistence of plastics is creating risks for ecosystems and climate stability in the long term, plastics are deeply embedded in our modern life, used in everyday items like medicine, packaging, construction and electronics. Efforts to cut production, such as a global plastics treaty, remain slow and fiercely contested, as major petrochemical producers resist binding caps.
Plastic production continues to rise rapidly as a consequence. UN agencies state that 400-430 million tonnes of plastic are produced each year and about half is meant for single‑use items such as packaging, straws, etc. Less than 10 per cent is recycled, and without intervention, global plastic production may triple by 2060.
Since plastics degrade extremely slowly, most of the material ever produced still exists. Researchers estimate that over 8 billion tonnes of plastic have been produced globally, with around 80 per cent ending up in landfills or the environment.
The study urges governments and international bodies not to treat plastic pollution and the climate crisis as separate challenges.
It calls for measures such as cutting single-use plastics, improving waste management, promoting biodegradable alternatives, and investing in research to better understand how microplastics affect ocean temperature and carbon cycles.
Researchers suggest the UN Sustainable Development Goals should better reflect the risks posed by microplastics, noting that plastics are currently covered by only a single indicator.
“Our next step is to quantify the climate impact of microplastics and develop integrated solutions,” Dr Obaidullah said.
“This is not just an environmental issue; it’s a global sustainability challenge.”
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