According to Dominic Lawson, in a Times article on 30 December 2018, the amount of plastic being used in the from of plastic bags has actually increased, even though the number of bags issued by supermarkets has reduced. This is because people are opting to pay 10 pence for the stronger and thicker "bags for life" rather than pay 5 pence for the thin single use bags.

Dominic continues his article by referring to a UK government report into the subject in which it compares the overall carbon dioxide emissions required to produce a bag, taking into account the number of times it is used. The conclusions showed that a paper bag had to be used 3 times to be better for the environment than a single use plastic bag used only once. A cotton bag had to be used 173 times to achieve the same result.  

In fact the problem with plastic is not that it causes global warming, but that it is not being disposed of safely, and that is an issue for law enforcement. Until all nations have proper control of waste disposal there will be problems of dumping waste in rivers and the sea.