What is the real cost of a plastic bag?

While many billions of plastic bags are used each year, their contribution to climate change is actually minimal. In his book Carbon Detox, the environmental writer George Marshall calculates that on average, our annual use of plastic bags produces only 5 kg of the enormous 12,500 kg of carbon dioxide we pump out each year.

So the environmental impact of our use of plastic bags is tiny in comparison to everything else we get up to. True, they don't disappear quickly and tend...