Microplastics weaken the ocean’s ability to absorb carbon

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How microplastics stifle phytoplankton

The Earth’s oceans act as a massive, natural carbon sink, performing a task that no man-made machine has yet replicated at scale. According to research led by the Norwegian University of Science and Technology (NTNU), this process relies heavily on phytoplankton—single-celled algae that convert sunlight and CO2 into oxygen and sugar. The introduction of microplastics into this ecosystem creates a mechanical and chemical blockade. Some plastics, specifically PVC, are directly toxic to these algae. Others act as physical barriers, blocking sunlight from reaching the depths required for photosynthesis or triggering oxidative stress that disrupts cellular function. “The ocean plays a crucial role in absorbing carbon from the atmosphere. Between 25 and 30 per cent of all human-generated CO2 is absorbed by the ocean,” “Phytoplankton plays an important role in this process. So, what happens if marine microplastics affect the plankton?” Francesca Verones, NTNU Department of Energy and Process Engineering The impact is not distributed evenly across the globe. The regions where carbon uptake is most critical—arid and tropical zones—are also where microplastics cause the most significant damage. NTNU researchers calculated the following annual reductions in carbon absorption:

• Arid regions: 25,000 tons per year
• Tropical regions: 48,000 tons per year

Because almost all plastic discarded into the environment eventually migrates toward the ocean, these concentrations are expected to rise, further eroding the planet’s primary defense against atmospheric carbon buildup.

The atmospheric heating effect of colored plastic

While the ocean’s capacity to absorb carbon is shrinking, the atmosphere is gaining a new, overlooked heating agent. For years, climate models treated airborne microplastics as clear, colorless beads. However, real-world plastic is dyed, weathered, and pigmented. A study led by Hongbo Fu of Fudan University found that colored plastic particles absorb sunlight roughly 75 times more strongly than clear ones. Using electron energy-loss spectroscopy (EELS), Professor Drew Shindell and his team determined that the color of the debris dictates its thermal impact: yellow, black, red, and blue fragments absorb light far more aggressively than lighter hues. “The key finding is really that the warming strongly outweighs the cooling,” Professor Drew Shindell, via Science Direct This airborne plastic functions similarly to black carbon (soot from burning fuels), though on a smaller scale. Globally, Fu’s models suggest that airborne microplastics produce a warming effect equal to about 16 percent of that produced by black carbon. The regional disparity is even more stark. Over the North Pacific Subtropical Gyre—the area known as the garbage patch—the warming effect from airborne plastic is roughly 4.7 times that of black carbon. This spike occurs because wave action and sea spray launch ocean plastics into the air in a region where the skies are otherwise relatively clean of industrial soot.

The Basel Convention’s terminology conflict

The scientific reality of plastic as a climate driver is colliding with a rigid regulatory framework. In 2018, the Norwegian government pushed to classify plastic as potentially hazardous waste under the Basel Convention, leading to the Plastic Amendments that took effect in January 2021. However, the legal language used in the Convention—specifically the terms “waste” and “disposal”—is creating a policy bottleneck. These terms were originally designed for nuclear and chemical waste, implying an end-of-life treatment. In the context of plastics, this terminology clashes with circular economy goals, which prioritize the recovery and reuse of materials. The friction manifests in three primary ways: Norway has since submitted a proposal to the Basel Convention’s Open-ended Working Group (OEWG) to clarify these classifications. The goal is to strengthen implementation without accidentally undermining the global trade of semi-processed plastics that enables circular recycling markets to grow.

The thermodynamic feedback loop

When synthesized, these findings suggest that microplastics are not merely a pollution problem—they are a thermodynamic catalyst. We are seeing a simultaneous attack on the planet’s temperature regulation: the ocean’s “lungs” (phytoplankton) are being suffocated, while the atmosphere is being filled with microscopic, heat-absorbing particles. While the warming effect of airborne plastic is modest compared to the burning of fossil fuels, it represents a systemic failure of waste management that has evolved into a climate variable. The uncertainty remains in the exact volume of these particles currently suspended in the atmosphere, but the laboratory data on how they interact with sunlight is definitive. “it just adds another compelling reason why we should pay more attention to keeping plastic waste out of the environment” Professor Drew Shindell The next 30 days of climate discourse will likely focus on whether these findings necessitate a re-evaluation of global carbon budgets. If the ocean’s absorption rate is declining due to plastic toxicity, the “safe” threshold for human CO2 emissions may be even lower than previously calculated.