About 1.3 billion tonnes of discarded plastic will litter the land and sea by 2040 unless worldwide action is taken, a new study estimates.
Dr Costas Velis from the University of Leeds said the number was "staggering" but that we had "the technology and the opportunity to stem the tide".
The report is published in the journal Science.
"This is the first comprehensive assessment of what the picture could be in 20 years' time," Dr Velis explained. "It's difficult to picture an amount that large, but if you could imagine laying out all that plastic across a flat surface, it would cover the area of the UK 1.5 times.
"It's a complex model because plastic is everywhere and in every part of the world it's different in terms of how they use and deal with it. But our model tries to simplify that reality and come up with the numbers."
The team's calculations were based on tracking the production, use and disposal of plastic around the world. The team then created a model to "forecast" future scenarios. The "business as usual" scenario was based on the current trend of increasing plastic production and no significant change in the amount of reuse and recycling.
Adjusting those parameters allowed the researchers to project how much of a difference interventions would make - such as increased recycling, reducing production and replacing plastic with other materials.
Even if "all feasible action" was taken, Dr Velis explained, the study projected there would be 710 million extra tonnes of plastic waste in the environment by 2040.
There is no "silver bullet solution", for the plastic problem, but an often overlooked issue that this study highlighted was the fact that an estimated 2 billion people in the Global South have no access to proper waste management.
"They have to just get rid of all their rubbish, so they have no choice but to burn or dump it," said Dr Velis.
Despite playing a major role in reducing global plastic waste, the roughly 11 million waste pickers - people who collect and sell reusable materials in low-income countries - often lack basic employment rights and safe working conditions.
Dr Velis said: "Waste pickers are the unsung heroes of recycling - without whom the mass of plastic entering the aquatic environment would be considerably greater."
He said policies to support them and make their work safer were a vital part of solving this problem.
Dr Ian Kane, from the University of Manchester, who was recently part of a team that calculated the amount of micro-plastic in the seabed, described the picture the researchers had painted as "horrifying".
"The authors are clear that there are large uncertainties in the data and analysis but regardless of the exact figures, the increasing rate of plastic production to meet increasing global demand has pretty dire consequences for the environment," he told BBC News.
Steps the researchers called for included:
- Reducing growth in plastic production and consumption
- Substituting plastic with paper and compostable materials
- Designing products and packaging for recycling
- Expanding waste collection rates in middle/low-income countries and supporting the "informal collection" sector
- Building facilities to dispose of the 23% of plastic that cannot be recycled economically, as a transitional measure
- Reduce plastic waste exports
Prof Jamie Woodward, also from the University of Manchester, pointed out the irony in this scenario being laid out during the pandemic.
"Plastic has kept many frontline workers safe through this," he said. "But PPE waste over the next decade could be horrendous.
"There are parallels with the climate change problem in that business as usual will be disastrous. We need to radically change our behaviour."