Europe has sent just over half the plastic waste it used to ship to China to other parts of Asia since Beijing's environmental crackdown closed the world's biggest recycling market in January. The knotty problem is what to do with the rest.
Some of the surplus is piled up in places from building sites to ports, officials say, waiting for new markets to open up. Recycling closer to home is held back by the fact that the plastic is often dirty and unsorted, the same reasons China turned it away.
Countries led by Malaysia and Vietnam and India imported far more of Europe’s plastic waste in early 2018 than before, European Union data show, but unless they or others take more, the only options will be to either bury or burn it.
In an overcrowded continent where landfills are much more restricted than elsewhere, burning is the obvious option to help generate electricity or heat from hundreds of thousands of tons of surplus waste.
But more radical ideas, such as putting oil derived plastic back underground to "mine" back when recycling becomes more sophisticated, are being aired as Europe tries to work out what to do.
European waste policies "need to become much more nuanced, because some landfill might actually be quite good," professor Ian Boyd, chief scientific adviser for the British government's department of environment, food and rural affairs, told Reuters.
"I'm putting out a challenge to the current system," he said, referring to the fact that waste policies in Europe either ban or limit landfill but do little to restrict what has been dubbed "skyfill" — the release of pollutants into the air.
Europe has favored the construction of power plants that burn waste for electricity or heat because land is scarce and landfills produce toxins and greenhouse gases such as methane as organic waste — from food to nappies — rots.
Waste-to-power plants produce greenhouse gas emissions too, but in most of Europe they are exempt from carbon taxes that stand at about 14 euros a ton in an industrial market.
Boyd said buried plastic could become a valuable resource only if the penalties for emitting greenhouse gases, both in making plastics and burning them, were far higher than today.
Globally, plastics accounted for 390 million tons of carbon dioxide emissions in 2012, ranging from production to incineration and equivalent to the emissions by a nation such as Turkey, according to the Ellen MacArthur Foundation, a think-tank that specialises in recycling.
The plastics industry takes issue with such assessments, saying they ignore the vast contribution of plastic in reducing other emissions — by preserving food and reducing the weight of transport, for example.
The Confederation of European Waste-to-Energy Plants (CEWEP), a group of some 400 plants using 90 million tons of municipal waste to provide heat and electricity for millions of people, said burying and then mining back plastic was a fantasy.
"Digging waste into landfills and then waiting until a magic technology pops up in the future is not a responsible option," CEWEP managing director Ellen Stengler said, adding that the idea was a minority view she heard "here and there" in Europe.
Just cleaning plastic waste before burial would be hugely expensive, plastic would degrade underground and there would be risks such as fire, she said.
The latest major U.N. assessment of climate change, in 2014, also floated the idea that cities might sort and bury waste such as metals, paper and plastics to create "a material reservoir that can be mined" sometime in future.
Plastic pollution is surging and could, according to UN Environment, exceed the weight of fish in the oceans by 2050.
China, which used to process half the world's exports of plastic waste, has insisted on higher standards of cleanliness and sorting to prevent waste that cannot be recycled being burned, which, in its case, often means in open pits.
For Europe, the restrictions have so far acted as an effective ban, according to official data reviewed by Reuters which showed exports to China crashing by 96 percent in the first two months of the year.
Nations led by Malaysia, Vietnam, Turkey, India and Indonesia took on around 60 percent of the waste, but the surplus means Europe's market for low-grade waste has collapsed.
A ton of plastic waste for export, with up to 20 percent impurities such as paper labels, could be sold for between 25 and 40 pounds a ton in April 2017, according to British recycling group letsrecycle.com.
Last month, by contrast, you had to pay between 40 and 60 pounds to get someone to take it away.
Despite this, Patawari Borad of the Bureau of International Recycling in Brussels said recycling within Europe had not increased dramatically. "One can only guess that this unsorted material is going for either energy or incineration."
Waste-to-energy body CEWEP said it saw no sign extra plastic was being burned. Incinerators would notice a higher share of plastics, Stengler said, because, ton for ton, they produce a lot of energy.
Proponents of the idea of burying plastic include Keith Freegard, a director of Axion Polymers in England, one of Europe's leading recyclers of waste from cars and electronics.
"All those tons of carbon-rich waste material that were going into the landfill are now being released into the sky. Why are we allowing this free access to 'skyfill'?" said Freegard, who is vice chair of the British Plastic Federation’s Recycling Group.
"We should separate and store plastic in a well-controlled landfill as a future mine," he told Reuters.
To produce a megawatt hour of electricity, he said a waste-to-energy plant would need to burn 345 kg of plastic, emitting 880 kg of carbon dioxide. By contrast, a gas-fired power plant would generate the same amount of energy by burning 132 kg of natural gas, emitting just 360 kg of carbon dioxide.
Stengler and nations that favor waste-to-energy plants say such accounting is misleading and that waste-to-energy helps replace fossil fuels, a key goal of the 2015 Paris climate agreement to limit heat waves, floods, droughts and rising seas.
Swedish government estimates, for instance, show that three tons of municipal waste contain as much energy as a ton of oil.
World production of plastics has increased about twentyfold since the 1960s and is expected to double again over the next 20 years, according to the European Commission.
Erik Solheim, head of U.N. Environment in Nairobi, said the global focus for plastic policies should be to cut use, especially products such as microplastics used in some cosmetics or drinking straws that he said were unnecessary.
"The best of all is to avoid the plastics we don't need," he said.