We use reusable bags for shopping in place of plastic bag formerly given at shop for free. Restriction on the use of plastic bag seems to prevail now across Japan. However, there is a warning that they are creating new environmental problems. Thick plastic and durable cloth bags have higher carbon footprints than single use plastic bag.
In addition, to assess the environmental impacts of a bag, the following factors need to be taken into consideration: weight, manufacturing process and how to dispose of it. For example, to manufacture cotton cloth it needs a lot of water, insecticide and fertilizer which result in nitrous oxide, another greenhouse gas.
Danish Environmental Agent reports that a cotton bag should be used at least 7100 times to offset the environmental impact when compared to single use plastic bag. They used 15 different environmental indicators in this estimation such as climate change, ozone layer depletion, air pollution, water use and land use. This number is reduced significantly to 52 when it comes solely to climate change.
Likewise, plastic bag has relatively smaller impact on climate change than other pollutions that it causes, such as microplastic pollution. Whether it is plastic or cotton bag, it is better to reuse as much as possible.