ACCORDING TO THE United Nations Environment Programme (UNEP), up to 5trn plastic bags are consumed each year. Disposed of improperly, they can clog waterways, choke marine life and provide a breeding-ground for malaria-carrying mosquitoes. When dumped in landfills, they can take centuries to decompose.

Plenty of governments have decided that enough is enough. On July 20th Panama became the latest to ban single-use plastic bags. More than 90 countries have similar restrictions (Tanzania and New Zealand recently implemented their own bans). Another 36 regulate them with levies and fees. Bans are particularly widespread in Africa. This is partly because relatively low waste-collection and recycling rates make the problem of waste plastic more visible, partly because Africa exports very little plastic and lacks a strong industry lobby.

The resulting international patchwork of laws has lots of loopholes. Many countries regulate just one part of the plastic-bag lifecycle, such as manufacture, distribution or disposal. The most common approach is to charge shoppers at the till. Although this reduces local demand for bags, it does not stop them being exported. At least 25 countries with bans—including Panama—have exemptions for perishable foods or medicines.

Some environmentalists reckon that policymakers should in any case focus their efforts elsewhere. Plastic pollution is hard to miss, but its effects are small compared with global warming or biodiversity loss. The alternatives to plastic are pretty rubbish, too. For a cotton tote bag to generate less greenhouse-gas emissions than a throwaway plastic one, it has to be used 131 times.