In brief (March 2015, part II): plastic pollution and planetary boundaries

Two more picks from what I’ve read over the past couple of months:
marine plastic pollution, or how much plastic waste reaches the oceans,
planetary boundaries, or how to define the environmental limits within which human societies may safely develop.

  • Marine plastic pollution

Plastics were commercially developed in the 1930s and 1940s. As their presence in our daily lives increased, so did the presence of plastic debris in Earth’s oceans. Plastics that are buoyant in seawater, such as polyethylene and polypropylene, can be spotted along coastlines, or even more impressively perhaps, as huge masses of floating debris in ocean gyres. However, plastic debris can also be found in other places, such as in Arctic sea ice, or on the sea floor, and they can be degraded into particles small enough to be ingested by even small marine invertebrates. On the whole, plastic pollution is a matter of increasing concern because of its effect on oceans and marine wildlife, but also because of the long half-life of plastic in the environment and its ever increasing production, consumption, and waste.

In a recent study, researchers tried to quantify how much mismanaged plastic waste (that is, waste littered or not properly disposed of) reaches the oceans from coastal populations worldwide. To do so, they used a framework based on the amount of solid waste generated by capita, the percentage of it being plastic, the percentage being mismanaged and therefore likely to reach the oceans (especially in coastal areas), and measures of population density and economic development. They found that, of 275 million metric tons of plastic waste produced in 2010 in 192 coastal countries, about 99 million metric tons came from coastal areas, and about a third of that was mismanaged, resulting in 5 to 13 million metric tons of plastic waste entering the oceans (about 2-5% of the total plastic waste generated in those countries).

While these are general figures, the researchers noted that the top 20 countries that produce the most mismanaged plastic waste out of the 192 studied accounted for about 80% of the total mismanaged plastic waste. Of these, 16 countries were middle-income countries with likely fast-growing economies but poor waste management infrastructure, highlighting the importance of improving such infrastructures as countries develop. However, the researchers also noted that even countries with a good track record of waste management may still be responsible for high amounts of mismanaged plastic waste reaching the oceans, simply because of the size of their coastal populations and a high level of waste generation per individual. The US are a typical example of that situation, ranking 20 (out of the 192 countries studied) for their mass of mismanaged plastic waste produced. The 23 coastal European Union countries, if considered collectively, would rank 18. Both the US and the EU thus highlight the fact that good management infrastructures are not enough, and that reducing plastic waste generation in general should be an important goal.

(Jambeck et al. Science 13 February 2015. doi: 10.1126/science.1260352)

  • Planetary boundaries

The planetary boundaries concept was first introduced in 2009 and aimed to define the environmental limits within which human societies may safely operate without destabilizing the Earth System (which is the interactions between land, ocean, atmosphere, and life that together make up the conditions upon which human societies depend). To do so, scientists identified nine global processes that are crucial to the stability and resilience of the Earth System and that are subject to human-driven changes: climate, biosphere integrity, stratospheric ozone, ocean acidification, biogeochemical flows, land-system use, freshwater use, atmospheric aerosol loading, and introduction of novel entities (for example, pollutants). They then combined the current scientific understanding of the Earth System with the precautionary principle to define planetary boundaries – levels of human-driven perturbations below which the risk of destabilizing the Earth System remains low. The idea is that transgressing a boundary increases the risk of pushing the Earth System into a much less hospitable state for human life as we know it (that is, the contemporary human societies that have developed over the past 11,700 years during the relatively stable Holocene epoch, which started as the last glacial period ended).

Scientists have now updated the initial planetary boundaries based on the scientific advances of the past five years. They have also improved the framework by developing boundaries at a more regional level, so that it can be applied to develop sustainability policies both at a global and at a regional scale. Importantly, the update shows that four of the nine planetary boundaries have now been crossed as a result of human activities. These boundaries are: climate change, loss of biosphere integrity (biodiversity loss and species extinction), land-system change (for example, deforestation), and altered biogeochemical cycles (phosphorus and nitrogen cycles).

(Steffen et al. Science 13 February 2015. doi: 10.1126/science.1259855)

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