Читать книгу Plastics and the Ocean - Группа авторов - Страница 16

At present, plastic production is a relatively energy‐efficient operation supporting a vast global manufacturing industry providing an array of useful products at a resource cost of only about 4–6% of the annual global petrochemical demand (compared to the ~50% used for transportation). The embodied energy² EE (MJ/kg) of a material is a useful measure of how “energy‐expensive” a given material might be and is the sum of all energy expenditure associated with producing a unit mass of the material or a functional unit of a product. This energy is not “embodied” in a product in the sense that all such energy can be recovered from the material. Market cost, however, is an unreliable guide to the EE of a material or product. Common plastics generally have a lower EE compared to metal, close to that of glass, but higher than that of wood. Most of this energy is typically derived from fossil fuel, a dwindling non‐renewable resource that should invariably constrain global plastics production. But, a shortage of feedstock is not expected, especially in the US, at least in the foreseeable future; the boom in natural gas in the US (with about 500 trillion ft³ of proven gas reserves) guarantees the availability of low‐cost feedstock for plastics at least the next couple of centuries. Also widely anticipated is the freeing up of about 45% of the demand on global crude oil for gasoline production because of the expected growth in electric vehicles worldwide (CIEL 2021). The petrochemicals sector, including plastics, will then become the major driver for the petroleum industry, accounting for about a third of the future oil demand (IEA 2020).

As shown in Figure 1.3, manufacturing plastic resin requires a regular supply of fossil‐fuel feedstock, a source of processing energy, as well as commons resources such as air or water, a category often either overlooked or incompletely accounted for in calculating the cost of the product, shown on the left side of the figure. In the process, the carbon in the feedstock is sequestered in the plastic resin, while that used as fuel to generate energy for the operation is released as CO₂. A suite of externalities that impact air, water, and the generation of solid waste accompany the manufacturing process. The result of this operation are plastic resin pellets. These resin pellets must be transported and further processed thermally to be shaped into useful consumer products that we are familiar with. This also requires additional energy and results in emissions, though to a relatively lesser extent compared to in manufacturing. It is the combination of these externalities, referred to as “embodied impacts,” from manufacturing, use, and disposal, that is a major concern given the already‐apparent signs of man‐made climate change.

Figure 1.3 Schematic representation of the manufacturing process for plastics resin.

Global plastic production will keep increasing in the foreseeable future, especially given the availability of low‐cost feedstock and the growing demand for resin. Even at present, the plant capacity for resin production both in the US and globally exceeds the current demand for resin. But, producers are already investing in additional plant capacity³ anticipating a higher resin demand in future years. By 2050, the consumption of oil used to manufacture plastics is expected to outpace that by automobiles (IEA 2018). As production volumes invariably determine future environmental impacts of the industry, estimating resin production in the medium term is of special interest. An approximate estimate of future demand for plastics might be based on the analysis given in Figure 1.4 that plots the global resin production (MMT) with the world population (in Billions), with the trend therein extrapolated into future decades. Historic data fit a second‐order polynomial model (R ² > 0.99) and when extrapolated using projected future global population, the plot suggests an annual resin production of about 1040 MMT in 2050 and 2410 MMT in 2100. However, implicit in the extrapolation is the assumption that current per capita consumption of plastics will hold in the future generations, that likely underestimate future plastic production; the per capita use of plastics in high‐income countries such as the US are expected to increase by 19% by 2050 (Kaza et al. 2018).

More sophisticated predictive models estimate even a higher volume of future production of 1100 MMT (World Economic Forum 2016), 1800 MMT (Ryan 2015), or 4000 MMT (Rochman et al. 2013) by 2050. While accurate projections of production volumes are always difficult to estimate, it is reasonable to expect this volume to be at least 1000 MMT by 2050.

Manufacturing plastic resin at this unprecedented scale will entail a set of unique global environmental challenges. Instead of the current demand of 4% of annual fossil fuel production, plastics will then require 20% of the production, and result in 15% of the global carbon emissions (World Economic Forum 2016). Particularly worrisome are the estimated unmanageable increases in global CO₂ emissions in that scenario. This carbon footprint is primarily associated with manufacturing, use, and disposal of plastics and is referred to as “embodied carbon” or “aggregate emissions”. Zheng and Suh (2019), based on 2015 production data, reported annual lifecycle emissions of 1.8 GTCO_2–e from plastics, that amounted to only 3.8% of the global emissions in 2015. With the entire chemical industry accounting for only about 15% (Edenhofer et al., 2014) share of global emissions, this is a reasonable figure considering the societal value of plastics. The future forecast, however, is bleak, with an estimated 6.5 GTCO_2–e annually emitted by 2050 or nearly three times the present value attributed to plastics (Zheng and Suh 2019). This could even reach 8.0 GTCO_2–e if all post‐use plastics are incinerated for energy recovery. That much of carbon emissions will not only be challenging to manage but will certainly make it difficult for the world to abide by the legally binding treaty agreed to by 197 parties (including the US) at the 2015 Paris Agreement, to hold global warming well below 2.0 °C (preferably to 1.5 °C) over the pre‐industrial levels. With the global average temperature being only 0.8 °C short of this limit in 2020, achieving this goal will be a challenge in any event. Dire effects consequent to human failure at controlling climate change, including heat waves, ice‐free Arctic summers, sea‐level rise, declining coral reefs, loss of biodiversity, and lower crop yields, are already evident (IPCC 2018).

Figure 1.4 Global plastic resin production versus the population.

While the above discussion centered around CO₂, it is by no means the worst greenhouse gas responsible for warming; methane, nitrous oxide, and fluorocarbons are much more efficient as greenhouse gases.⁴ Offsetting combustive CO₂ emissions by potentially better controlling the emission of greenhouse gases in other application areas may be of some help. With plastics, over 60% of the emissions arise from feedstock extraction or the resin production stage (either from oil extraction or fracking⁵ for natural gas extraction), making material recycling an attractive strategy to reduce CO₂ emissions. While carbon emissions were used here to illustrate the problems of embedded impacts, it is certainly not the only negative environmental impact of plastic manufacturing. Externalities include acidification of water, water pollution, marine aquatic toxicity, photochemical oxidants, eutrophication potential, human toxicity, and ozone depletion potential (Stefanini et al. 2020).

A major consequence of higher production of plastics will be the increase in the post‐consumer plastic waste stream, already ineffectively managed worldwide (Jambek et al. 2015; Lebreton and Andrady 2019). This burgeoning plastic waste not only impacts the municipal solid waste (MSW) stream that we poorly manage but also contributes to the unsightly urban litter. Unlike paperboard or wood, plastics do not biodegrade in any appreciable timeframe (see Chapter 11) and will persist as urban litter over an extended period of time. Cities with a high population density, such as Mumbai in India (76 800 persons/sq. mile), Karachi in Pakistan (49 000 persons /sq. mile), and Seoul in Korea (45 000 persons /sq. mile), will be particularly affected by the future plastic litter problem. A recent model based on population density (LandScan data), the GDP, and country‐level plastic consumption data, identified future global “hot spots” for plastic waste generation, assuming a “business as usual” scenario (Lebreton and Andrady 2017). Worst affected regions in the next decades were identified as South Asia, East Asia, and South East Asia on a regional basis and China, India, and the Philippines on a country basis.

Geyer et al. (2017) estimated 42% of the plastics entering the waste stream at present to be packaging‐related. The MSW in affluent countries is already rich in plastic packaging waste (Kaza et al. 2018). The fraction of all plastics in the MSW stream in the US has grown from negligible levels in 1970 to 16.3% by weight (357 MMT) by 2018, with PET, PE, and PP making up 32% of the total plastic waste. Plastic waste generation (PWG) per capita varies with the affluence of the country. Compared with the PWG of 88 ̶ 98 kg/year per capita for affluent countries such as Korea and the UK, less wealthy countries like India, China, and Pakistan generate only 13–19 kg/year per capita. The US has the highest PWG of 130 kg/year per capita (Law et al. 2020).

Proliferation of single‐use plastic packaging, including beverage bottles, single‐serve sachets, dessert cups, and disposable bags, has exacerbated the situation, especially in the more affluent countries (Geyer et al. 2017). How the generated plastic waste is managed also varies geographically, depending on the availability of adequate infrastructure. In affluent countries, a combination of landfilling and incineration is used, with the US relying heavily on landfilling.