A Science Advances research article (2017-07-19) analyzed the global production, use, and final destination of plastics. The research article estimated that 8300 million metric tons (Mt) of primary or virgin plastic have been produced from the start of mass plastic productions post-World War II through 2015. Based on their data, the researchers estimate that 12,000 Mt of plastics will be in landfills or the natural environment by 2050. From the research article:

A world without plastics, or synthetic organic polymers, seems unimaginable today, yet their large-scale production and use only dates back to ~1950. Although the first synthetic plastics, such as Bakelite, appeared in the early 20th century, widespread use of plastics outside of the military did not occur until after World War II. The ensuing rapid growth in plastics production is extraordinary, surpassing most other man-made materials. Notable exceptions are materials that are used extensively in the construction sector, such as steel and cement.

Instead, plastics’ largest market is packaging, an application whose growth was accelerated by a global shift from reusable to single-use containers. As a result, the share of plastics in municipal solid waste (by mass) increased from less than 1% in 1960 to more than 10% by 2005 in middle- and high-income countries. At the same time, global solid waste generation, which is strongly correlated with gross national income per capita, has grown steadily over the past five decades. …

We estimate that 2500 Mt of plastics—or 30% of all plastics ever produced—are currently in use. Between 1950 and 2015, cumulative waste generation of primary and secondary (recycled) plastic waste amounted to 6300 Mt. Of this, approximately 800 Mt (12%) of plastics have been incinerated and 600 Mt (9%) have been recycled, only 10% of which have been recycled more than once. Around 4900 Mt—60% of all plastics ever produced—were discarded and are accumulating in landfills or in the natural environment….None of the mass-produced plastics biodegrade in any meaningful way; however, sunlight weakens the materials, causing fragmentation into particles known to reach millimeters or micrometers in size. Research into the environmental impacts of these “microplastics” in marine and freshwater environments has accelerated in recent years, but little is known about the impacts of plastic waste in land-based ecosystems.

The growth of plastics production in the past 65 years has substantially outpaced any other manufactured material. The same properties that make plastics so versatile in innumerable applications—durability and resistance to degradation—make these materials difficult or impossible for nature to assimilate. Thus, without a well-designed and tailor-made management strategy for end-of-life plastics, humans are conducting a singular uncontrolled experiment on a global scale, in which billions of metric tons of material will accumulate across all major terrestrial and aquatic ecosystems on the planet. The relative advantages and disadvantages of dematerialization, substitution, reuse, material recycling, waste-to-energy, and conversion technologies must be carefully considered to design the best solutions to the environmental challenges posed by the enormous and sustained global growth in plastics production and use. [Citations Omitted].

 A New York Times article (2017-07-19) offered further details on the study:

Roland Geyer, the lead author of the study, said, “My mantra is that you can’t manage what you don’t measure, and without good numbers, you don’t know if we have a real problem.”

The authors, who come from the University of California, Santa Barbara, the University of Georgia and the Sea Education Association in Woods Hole, Mass., used plastic production data from a variety of sources to make their estimates. …

Dr. Geyer cautioned that recycling was not a cure-all for global plastic pollution. He said the sole benefit of recycling was to reduce the amount of new plastic being produced, adding, “We don’t understand very well the extent to which recycling reduces primary production.”

The features that have made plastic so important in the global market are the same ones that make it such a pervasive pollutant: durability and resistance to degradation.

Dr. Geyer said there was not enough information on what the long-term consequences of all this plastic and its disposal would be. “It accumulates so quickly now and it doesn’t biodegrade, so it just gets added to what’s already there.”

“Once we start looking, I think we’ll find all sorts of unintended consequences,” he added. “I’d be very surprised to find out that it is a purely aesthetic problem.”