As heavy rains and storms become more frequent more litter will be transported to the sea. Marine litter is projected to triple by 2040.
Marine litter consists of persistent and manufactured or processed materials that end up in marine or coastal environments, for instance through deliberate littering or by accidentally being lost at sea. The sources of marine litter are, however, not only to be found at sea or on shore, because marine litter can also consist of materials that have been transported by rivers, sewage and storms, for instance.
Marine litter has direct effects on marine and coastal environments but it does not operate in isolation. A fundamental and critical pressure on marine and coastal environments virtually everywhere is climate change. Interlinkages between marine litter and climate change were recently reviewed in an article by Susana Lincoln and co-workers that was published in Science of the Total Environment 1 . In addition to providing definitions of marine litter, the authors explain that plastics are the largest and most harmful fraction of marine litter, and account for at least 85% of marine litter. They also explain that “In the absence of interventions, at the current rate the amount of plastic waste entering aquatic eco-systems is projected to nearly triple from some 9–14 million tonnes/year in 2016 to a 23–37 million tonnes/year by 2040”. (The source for these pieces of background information was a report by UNEP2 .)
Here we highlight some of the findings of the study, especially regarding climate change effects on the transport of litter, and ecosystem and biodiversity effects. A very basic coupling between marine litter and climate change is the fact that climatic phenomena that are driven by climate change affect the sources and transport of marine litter. For instance, heavy rain can increase the transport of microplastics and litter from land to rivers, which ultimately transport these materials to estuaries. Heavy rain also increases run-off from rivers and therefore affects the magnitude of riverine transport. Another climatic effect that increases the transport of litter from land to the sea is the occurrence of storms that cause erosion, and hence lead to the release of litter that has been trapped or buried on beaches and other coastal sources.
The threat of erosion is moreover worsened by climate-change-driven sea level rise. Climate factors that are literally extreme are extreme weather events, such as cyclones and hurricanes. Storm surges as well as heavy winds and rain are factors that cause significant transport of debris to the sea during such weather events. Climate change also affects the transboundary nature of marine litter because winds and currents transport litter around. Many large-scale weather phenomena are susceptible to climate change. One such example is El Niño and La Niña, although it is not clear how these events will change in the future. Nevertheless, the authors conclude that “Should there be any significant, long-term changes in oceanic and atmospheric circulation and in the timing and duration of El Niño and La Niña phases, this could change how and where marine litter ends up in our oceans”. In addition to all these relationships between climate change and the transport of marine litter, climate change can affect the breakdown of marine litter and perhaps especially that of plastics.
Rising temperatures can speed up the breakdown of plastics into smaller fractions and eventually into micro- and nano-plastics. Additionally, mechanical abrasion can occur as a result of large waves and strong currents. Storms can also lead to the resuspension of particles in the water.
As evidenced by these highlights, climatechange-related phenomena can affect the fate of marine litter in many ways. Just as importantly, climate change and marine litter can have cumulative effects on ecosystems and biodiversity, and the authors warn that “There are growing concerns that the interaction between marine plastic pollution and climate change can significantly impact marine biodiversity, and that this impact is set to accelerate and worsen worldwide over the coming years and decades, conflagrating to diminish the adapting capacity of the world’s oceans”. Although the authors acknowledge that there are knowledge gaps concerning the interactions between marine litter and climate change pressures, the effects of these combined threats are considered for several groups of species and several habitats.
Marine megafauna, for instance, are particularly vulnerable to plastics, and based on their review the authors report that half of the species (out of a total of 663 species) are suffering from marine litter (especially plastics). Around 30% of sea turtles and birds, as well as 4% of marine mammals, reportedly have plastics in their stomachs. Special attention is called for regarding seabirds, especiallyas their distributions are shifting because of climate change, and the interactions between seabirds and plastics are therefore also changing.
Among several habitats that are taken into consideration, one that appears to be especially susceptible to interactions is the habitat of sandy beaches. It is predicted that with the continued accumulation of plastics in this habitat over the coming decades, the resulting load of microplastics in the sand will lead to an increase in the temperature of the sand by approximately 2.4°C. A predicted parallel increase of 0.24°C per decade due to global warming will be superimposed. Through these parallel processes “an overall decline in the suitability of beaches for biodiversity” is therefore foreseen. Apart from reviewing interactions that concern species, habitats etc. (many of which could not be included here) the study also provides case studies from five different biogeographical regions, namely the deep sea, remote small oceanic islands, the Mediterranean Sea, the Caribbean Sea, and the polar sea-ice environments in the Arctic and in Antarctica. The findings of these case studies are summarised in Figure.
Marko Reinikainen
Sources and further reading:
1 Susana Lincoln et al., 2022. Marine litter and climate change: Inextricably connected threats to the world’s oceans, Science of The Total Environment, Volume 837. https://doi.org/10.1016/j. scitotenv.2022.155709
2 UNEP, 2021. From Pollution to Solution: A global assessment of marine litter and plastic pollution. https://www.unep.org/resources/pollutionsolution-global-assessment-marin...
Figure. Interactions between climate change and marine litter in five different biogeographical regions (from source no. 1).
