Plastics have become an integral part of modern life, from packaging and healthcare to aviation and agriculture. But their widespread use comes at a high environmental cost. Estimates that Approximately 4.8 to 12.7 million tons of poorly managed plastic waste enters the environment each year, with up to 40 % of this amount being single-use plastics. This waste gradually breaks down into smaller fragments known as microplastics (MPs), which are particles smaller than 5 mm. Although research has long focused on identifying and cleaning this pollution, new evidence suggest that microplastics play a key, albeit hitherto little-researched, role in climate change and the health of the world's oceans.

Microplastics and the disruption of the carbon cycle

The oceans act as the largest carbon sink on the planet, absorbing approximately 25-30 % of carbon dioxide (CO2) produced by human activities. This process is mainly ensured by biological carbon pump, in which phytoplankton and zooplankton play a key role. Phytoplankton, through photosynthesis, bind atmospheric CO2 into biomass, which sinks to the ocean floor after dying.

However, microplastics seriously disrupt this mechanism. The presence of high concentrations of MPs at the sea surface can reduce light penetration, which negatively affects phytoplankton growth and their photosynthetic efficiency. In addition, zooplankton often mistake microplastics for food, leading to reduced natural food intake, impaired metabolism, and ultimately a slowdown in the process of carbon storage in the deep ocean. Studies suggest that exposure to microplastics can accelerate the breakdown of crustacean (krill) fecal pellets, which can lead to a loss of up to 27 % ocean capacity to sequester carbon.

Direct greenhouse gas emissions and the „plastisphere“

Microplastics are not just passive pollutants; during their degradation in the natural environment, they directly release climate-active gases such as CO2, methane (CH4) and ethylene. This process is driven mainly by UV radiation, which causes photodegradation of polymers.

Another complex factor is the so-called. plastisphere – a microbial community that colonizes the surface of plastics in the oceans. These microbial biofilms can alter the cycling of important nutrients such as nitrogen and phosphorus. Microbial activity within the plastosphere can lead to the breakdown of organic carbon and the subsequent production of CO2, further increasing the overall carbon footprint of plastics in the ecosystem.

Ocean warming and acidification

The link between microplastics and ocean warming is becoming increasingly clear. MPs floating on the surface can change the albedo (reflectivity) of the water. Darker-colored particles have the potential to absorb more solar radiation, which can lead to local warming of the water column. Simulations on beaches have shown that adding microplastics to sand can increase its temperature, which has a direct impact, for example, on the nesting success of sea turtles, for whom the incubation temperature determines the sex ratio of hatchlings.

In addition to warming, microplastics also contribute to ocean acidification. Abiotic leaching of organic matter from plastics lowers the pH of seawater. Higher acidity negatively affects organisms that form limestone shells, such as corals, clams, and starfish, destabilizing entire food webs.

An obstacle to climate resilience and human rights

Microplastics also threaten the so-called. blue carbon ecosystems, such as mangroves and seagrasses, which are key to climate resilience. Plastic waste gets trapped in the root systems of mangroves, limiting the supply of nutrients and potentially leading to the death of these important plants, which otherwise efficiently store carbon.

According to the UN, microplastic pollution poses a global threat to human rights, including the right to health and a safe environment. MPs have been found in human blood, lungs, placenta and urine. Pollution also hinders the achievement of the Sustainable Development Goals (SDGs), particularly in the areas of good health (SDG 3), clean water (SDG 6) and ocean protection (SDG 14).

The Road to Recovery: An Integrated Strategy

As microplastic pollution and climate change are interconnected, addressing them requires a holistic approach. Key recommendations include:

• Ban on single-use plastics and promoting biodegradable alternatives.
• Transition to circular economy, which minimizes the need for new plastic production and improves recycling technologies.
• Use of artificial intelligence (AI) and machine learning to more accurately identify pollution sources and monitor them.
• Global collaboration as part of the upcoming International Plastics Treaty, which should address the entire life cycle of plastics from design to disposal.

Understanding the complex relationship between microplastics and climate is essential to protect future generations. Only coordinated international action and legislative changes can mitigate the invisible threat that these tiny particles pose to our planetary climate system. JRi

An analogy for better understanding: Imagine the biological carbon pump in the ocean as a giant conveyor belt, which constantly removes excess carbon dioxide from the atmosphere and stores it safely deep underground. Microplastics in this system function as sand in deposits – they scrub components (phytoplankton and zooplankton), slow down the belt movement, and sometimes cause the cargo to be dumped back into the atmosphere prematurely, stalling the entire process of cleaning the planet.

The study was published in the journal sciencedirect.com