Global plastic waste generation

Combining country-level data on self-reported per capita municipal solid waste (Waste Atlas, 2016) generation with high resolution (30 arc seconds) distributions of global population (Landscan, 2014) and GDP (UNEP/DEWA/GRID-Geneva, 2012), we estimated plastic waste generation at local level. The estimate reflects differences in consumption within a country, differentiating between consumption rates in urban and rural areas. Based on self-reported levels of inadequate disposal, we estimated between 60 and 99 (mid-point: 80) million metric tonnes (Mt) of municipal plastic waste were inadequately disposed globally into the environment during 2015 (Fig. 2). The quantity represents about 47% of the global annual municipal plastic waste generation (mid-point estimate of 181 Mt for n = 188 countries).

Fig. 2 Global mismanaged plastic waste (MPW) generation in 2015. Plastic waste generation is computed globally on a 30 by 30 arc seconds resolution reflecting geographical heterogeneity based on population and GDP distributions. National data on waste management reported per countries (Waste Atlas, 2016) is derived to estimate the mismanaged fraction at local scale. The 10 largest producing urban centres are labelled on the map with Manila, Cairo and Kolkata as the leading agglomerations Full size image

Hosting 60% of the global population (United Nations, 2015), the Asian continent was in 2015 the leading generating region of plastic waste with 82 Mt, followed by Europe (31 Mt) and Northern America (29 Mt). Latin America (including the Caribbean) and Africa each produced 19 Mt of plastic waste while Oceania generated about 0.9 Mt. However, the proportion of produced waste that was inadequately disposed varied across regions (Waste Atlas, 2016). We derived quantities of MPW from reported waste management data per countries and per capita GDP. As a significant level of uncertainty is associated with the data on municipal waste management, we introduced lower and upper ranges along with our midpoint estimate and thereafter reported the ranges in brackets. With an average of 63% of inadequately disposed waste for 2015, Asia released 52 (42–58) Mt of plastic waste into the environment, representing 65% of the global MPW generation. Africa, however, had the highest rate of unsound waste disposal with an average of 88.5% resulting in a total of 17 (10–20) Mt of unsoundly disposed plastic waste despite the low levels of resin production. Latin America and the Caribbean were the third generating region with 7.9 (6.7–8.3) Mt, followed by Europe with 3.3 (1.3–9.1) Mt, Northern America with 0.3 (0.03–3.0) Mt, and Oceania with 0.14 (0.05–0.32) Mt. Interestingly, except with Asia, the regions with unsoundly disposed plastics, do not correspond to production volumes of plastics in these regions; the Middle East and Africa account for only 7% of resin production while US and Europe each account for ~20% of global plastics production. The unfair practice of importing waste, especially e-waste, from developed nations, is to a large part responsible for this problem in Africa for example (Schmidt, 2006).

We ranked contributors by mid-point estimate of MPW generation at regional and national scale (Table 2). The generation of waste from the Asian continent was distributed between Southern, Eastern and South-East Asia with respectively 18.4, 17.4 and 11.7 Mt y−1 of annual MPW generation. Inputs from China with 17.2 Mt y−1, and India with 14.4 Mt y−1 dominated the waste generation figures for Asia. These two countries provide over a third of the global MPW generation. The Philippines were the third generating country with 4.52 Mt y−1 but Manila, its capital, was predicted as the largest urban centre for the generation of MPW with at least 0.81 Mt y−1 for the agglomeration, the same annual amount as produced by countries like Sudan or Algeria. Five of the top 10 countries for mismanaged plastic waste identified by this model include only 5 of the top ten countries identified by Jambeck et al. (2015) for 2010. Except for Tanzania, all ten were identified in the top 20 countries in this previous work. However, at least a part of this discrepancy might be due to differences in methodology adopted in previous and present studies. The finer granularity of the present model allows us to predict local scale accumulation. Solid waste is mostly an urban phenomenon (Hoornweg et al., 2013) and our model confirms this by predicting substantial accumulation around cities and near axes of transportation with 89% of global MPW produced over 10% of the total modelled landmass, and 64% over less than 1.5% (Fig. 3). High resolution renderings of MPW generation on land are presented in Supplementary Figure 4. We ranked global urban centres by MPW generation. Manila, the largest contributor predicted by our model, was followed by Cairo and Kolkata with 0.53 and 0.48 Mt y−1. Sao Paolo in Brazil was ranked fourth with 0.47 Mt y−1. The rest of the top 10 cities were in Asia with Bangkok (0.45 Mt y−1), New Delhi (0.41 Mt y−1), Shanghai (0.5 Mt y−1), Kuala Lumpur (0.29 Mt y−1), Beijing (0.28 Mt y−1) and Guangzhou (0.27 Mt y−1).

Table 2 Top regional and national generators of MPW in Mt y−1 for 2015 Full size table

Fig. 3 Distribution of annual MPW generation over total land surface area. Modelled cells were classified by rate of MPW generation (0–1, 1–10, …, >10k kg y−1). Total land surface area (blue, expressed in % of total modelled surface) and total MPW generation (grey, expressed in % of total generation) are represented for each cell category Full size image

Future scenarios

We predicted future plastic waste generation by considering population (United Nations, 2015) and GDP (IMF, 2016; OECD, 2014) growth rates per country. By 2020, under a business-as usual-scenario for plastic consumption, our predictive model suggested the world will produce above 200 Mt of municipal plastic waste annually and around 230 Mt by 2025. This is in good agreement with previous projections of solid waste generation (Hoornweg et al., 2013) with daily estimates above 6 Mt in 2025. Considering global average proportion of plastic in municipal solid waste (10.9%, lower: 8.3%, upper: 13.2%), a daily input of 6 Mt of solid waste may represent around 239 (182–290) Mt of annual generation of municipal plastic waste. Based on long term projections of population and GDP per countries, we estimated the global municipal plastic waste generation could reach 300 Mt annually by 2040 and 380 Mt by 2060. This increase is also in good agreement with municipal solid waste generation projections which are not expected to peak within this century (Hoornweg et al., 2013). To predict the total mismanaged fraction (MPW) of future plastic production, we initially considered two scenarios. In scenario A, we assumed the case of business-as-usual where the level of waste management remains at the current status in different countries worldwide. In scenario B, we assumed waste management efforts will improve with increased investment in infrastructure as the economies in individual countries grow in the future.

Following a growing demand of plastic by end-users, the MPW generation in scenario A would nearly triple from the present value of 80 (60–99) Mt y−1 to 213 (155–265) Mt y−1 by 2060. Midpoint plastic demand by end-users in Asia was projected to steadily increase from 99 Mt y−1 in 2020 to 151 Mt y−1 in 2040 and 193 Mt in 2060. If no efforts are made in waste management, generation of MPW in Asia could double from 52 (42–58) Mt y−1 in 2020 to 129 (104–150) Mt y−1 in 2060. India would become the largest MPW generating country by 2035 and would reach 46.3 (38.6–52.0) Mt y−1 by 2060, followed by China with 33.3 (28.1–36.8) Mt y−1 and the Philippines with 11.6 (10.1–12.4) Mt y−1. According to scenario A, cities like Manila, Cairo, Kolkata or New Delhi would reach the 1 Mt y−1 mark for annual MPW generation before 2060. However, if we assume a gradual improvement of waste management infrastructures with scenario B, we estimated that global MPW generation could peak before 2020 and decrease to 50 (22–94) Mt y−1 by 2060. In this case, the decrease of global MPW generation would mainly be driven by the rapid economic development in Asia. We found that the continent could reduce MPW generation below 30 Mt y−1 by 2040 and below 10 Mt y−1 by 2060. This scenario would mean reducing mismanaged waste below 10% of total generated waste by around 2030 for current major contributors such as China, Thailand, Indonesia or Turkey, and around 2060 for countries like India, the Philippines, or Vietnam. Our model shows how the main contribution to global MPW production would then shift from Asia to Africa. Our projections suggested that African demand by consumers for plastic will increase exponentially in the future decades from 23 Mt y−1 of municipal plastic waste in 2010 to 72 Mt y−1 in 2060. The demand for plastic by end-users in Africa was projected higher than in Northern America or Europe by 2035. Under this scenario, by 2060, 8 out of the 10 generating country will be an African country with Nigeria (3.08–6.46 Mt y−1), Congo (2.22–6.33 Mt y−1), Tanzania (1.16–6.42 Mt y−1), Ethiopia (1.01–4.10 Mt y−1), Niger (0.88–2.69 Mt y−1), Sudan (0.38–2.00 Mt y−1), Mozambique (0.82–1.64 Mt y−1) and Mali (0.47–1.78 Mt y−1).

Finally, we investigated an alternative option where demand of plastic per capita would substantially decrease in the future. We introduced a third scenario C, where waste management efforts improve as the economy of a country grows like in scenario B, but also where plastic use by households is reduced to 10% of municipal solid waste by 2020 and to 5% by 2040, reflecting willingness from country to curb waste generation and ban single-use plastics. This objective is reachable as some developed economies already demonstrates such low rate. Notably Denmark, first country to introduce a tax on plastic bags in 1993 for example, now reporting 1% of municipal waste composed of plastic (Waste Atlas, 2016). We found no significant relation between fraction of plastic in solid waste and per capita GDP. Some strong economies for example reported large fractions such as The Netherlands, largest reported figure for a developed economy with 19% of plastic in municipal solid waste. Under a scenario where countries would align to reduce fraction of plastic in municipal waste to below 5%, the global plastic waste generation would drop to around 140 Mt per year by 2040 but increase again to 2015 levels with nearly 180 Mt per year in 2060 as global population grows. Combined with a gradual investment in waste management infrastructure however, the global MPW generation could be reduced to a third of current value with annual average generation below 25 Mt y−1 before 2060 including 74% generated in Africa and 21% in Asia. Long term projections for global MPW generation for scenario A, B and C are presented in Fig. 4 as well as distributions per continent. A full breakdown of results per sub-region with confidence interval for 2020, 2040 and 2060 is given for scenario A, B and C in Supplementary Tables 2, 3 and 4.

Fig. 4 Future projections of global mismanaged plastic waste (MPW) generation and distribution per continent under three scenarios. Scenario A corresponds to a business-as-usual case where the level of waste management corresponds to data for 2015 and consumer demand for plastic increases with economy. Scenario B considers that waste management infrastructures improve as per capita GDP grows. Scenario C reflects a reduction in plastic demand per capita with fraction of plastic in municipal solid waste capped at 10% by 2020 and 5% by 2040, waste management gradually improves as in scenario B. (Top, graph) The global midpoint estimates for MPW generation are represented with thick lines while the shaded areas represent our confidence interval. (Bottom, maps) Continental distribution of MPW generation in 2020, 2040 and 2060 under the three investigated scenarios Full size image

Sources to ocean

The rapid accumulation of MPW on land can result in the contamination of waterways and eventually the marine environment. Through runoff, winds, and gravity, plastic debris slowly makes its way downhill and enters the sea from coastal environments (Jambeck et al., 2015) and through rivers (Lebreton et al., 2017). A first global estimate of plastic inputs from land to the sea for 2010 (Jambeck et al., 2015) proposed to consider municipal plastic waste generation for population living within 50 km from the coastline and assumed 25% (15–40%) of plastic waste from this population enters the ocean. Under this condition, we predicted a total of 20.5 Mt of MPW for coastal population in 2010. Following the study, this quantity may be converted to an annual global input into sea of 5.1 (3.1–8.2) Mt. The fraction of plastic waste entering the ocean may vary between locations, however. The magnitude and timing of plastic waste displacement on land is poorly known (Horton et al., 2017) and may be a function of topography, land use, climate, vegetation and, particle shape and size (e.g., microplastics may be more easily transported than larger, more complexly shaped debris).

Considering populations living within a fixed distance from the coastline may not always be representative of land-based sources to the ocean as plastic waste generated inland can be transported by rivers. Predicted accumulation of plastic waste on land can be distributed into watersheds (Lebreton et al., 2017). Here, we categorised watersheds by surface area considering that small watersheds are located directly at the coastline while larger watersheds may expand in land and form streams and rivers (Fig. 5). We grouped watersheds by orders of magnitude in surface area from coastal watersheds (<10 km2) to continental rivers (>1,000,000 km2). From our global distribution of mismanaged plastic waste for 2015, we estimated that 5% of waste was discarded directly near the coastline (watershed surface area < 10 km2) and 4% at proximity to the coastline (10 to 100 km2). This result shows that the majority (91%) of MPW was generated inside larger watersheds (>100 km2) and suggests that rivers may be a major vector of transport of plastic waste from land into the ocean. Over a quarter of the global waste was discarded into the watersheds of only 14 continental rivers (>1,000,000 km2, namely the Mississippi, the Nelson, the St Lawrence, the Amazon, the Paraná, the Congo, the Niger, the Nile, the Zambezi, the Volga, the Lena, the Amur, the Yangtze and the Ganges rivers).