Since 2004, China has been the world’s largest generator of waste, including plastics. And, since 2010 at least, China has been the largest source of waste plastic flowing into the world’s oceans.

To its credit, the Chinese government has tried to shrink the problem. In recent years, it’s forced retailers to charge for single-use plastic bags that aren’t biodegradable (with questionable success); Jilin province has banned such bags and food-service items outright. The tropical island of Hainan plans to impose an even wider ban starting in 2020.

Officials are also looking for alternatives. According to one analysis, Chinese production of bio-based (rather than petroleum-based) biodegradable plastics will more than double by 2022. That might boost the reputation of the plastics industry, under fire for choking the world’s oceans with its products. Unfortunately, it’s not likely to help the environment much.

The history of biodegradable plastics dates back to 1975, when a group of Japanese scientists discovered bacteria that consumed nylon. As byproducts, they produced naturally occurring gases such as CO2, as well as biomass in the form of more bacteria. Over subsequent decades, as plastic trash accumulated in landfills and the public became more aware of the extended periods required to degrade that plastic (centuries, in many cases), demand grew for commercial plastics capable of being broken down into natural components by micro-organisms.

These biodegradable plastics are generally more expensive than traditional plastics, so, even today, they remain confined to certain product niches, accounting for less than 1% of total global plastics production.

Alibaba goes green

A big push from China could change that. In 2017, Alibaba Group Holding and a set of consumer companies established a green packaging consortium committed to environmentally sound packaging, including biodegradable plastics.

Worse, due to differences in chemistry, biodegradable plastics can’t be recycled with ordinary plastics. This means they have to be separated out

At the beginning of 2018, 90% of the straws made at Soton Daily Necessities. YW, one of the world’s largest straw manufacturers, were made from traditional plastics. By the end of that year, the share had dropped to 60%, as production of paper and biodegradable plastic straws ramped up.

The question is how much this will improve the environment. There are two issues. First, a product marketed as “biodegradable” might only break down in highly specific environments that aren’t encountered in the natural world — such as in an industrial composter where temperatures reach 49ºC. Such composting facilities are rare in most of the world and all but non-existent in China.

This raises the risk that, ostensibly, biodegradable plastics will end up in landfills where — if they’re buried — the lack of oxygen will ensure they degrade as slowly as regular plastics, if at all.

Worse, due to differences in chemistry, biodegradable plastics can’t be recycled with ordinary plastics. This means they have to be separated out and in China — where urbanites have long resisted sorting their recyclables — that’s unlikely to happen for many years.

Second, even plastics that are designed to degrade in natural environments are unlikely to break down as quickly in the ocean, especially if they sink to cooler regions or are ingested by animals. In one study, biodegradable plastic bags eaten by green and loggerhead turtles only lost 3% to 9% of their mass after 49 days (the same bags were completely degraded in an industrial composter).

What makes this finding particularly dangerous is evidence suggesting that individuals are more willing to litter biodegradable items, on the assumption that nature will take care of them.

For the Chinese government, the advantages of encouraging the switch to biodegradable plastics are obvious: at a minimum, it places the burden of managing growing volumes of plastic waste on manufacturers. But, for now, the government would be wiser to focus on cutting down the use of single-use plastic products entirely.

One option, ideally suited to China’s top-down governance, is to encourage manufacturers to create bags designed for multiple uses (a carry-out bag that easily converts to a trash bag, for example) and to raise fees on bags that don’t meet that standard.

Next, it’s imperative that China stop the leakage of plastics and other trash from sub-standard landfills into rivers and — ultimately — the ocean. That will require the government to develop municipal recycling systems, modernise its landfills and incinerators, and undertake public education campaigns. It won’t be cheap, quick, or easy. But the alternative is that the world’s oceans, and China’s environment, continue to degrade.

• Minter is a Bloomberg Opinion columnist. This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.