First, the Good News. Cities that have banned consumer plastic bags have seen a decrease in the number of bags found in nature. Abandoned bags are not only an eyesore, they are also detrimental to birds, fish, and other fauna as the bags make their way from cities to oceans—and we definitely don’t need to add to the Great Pacific Garbage Patch.

Now, the Bad News. Despite the local clean-up factor, the environmental benefits of banning plastic bags remain to be seen. A recent life-cycle study from CIRAIG looked at the consequences of banning conventional, single-use, consumer plastic bags (made of high-density polyethylene) from the city of Montreal. The results challenged the conventional understanding of banning these bags.

A key question is what type of bag buyers and sellers use to replace the banned ones. The CIRAIG study looked at the environmental impacts of seven alternatives:

Single-use bags

Oxo-biodegradable bags

Compostable bioplastic bags

Low-density polyethylene bags

Paper bags

Reusable bags

Woven polypropylene bags

Unwoven polypropylene bags

Cotton bags