The paper versus plastic bags debate has intensified in recent months as Canadians grow more concerned about the environmental impact of single-use plastics. 

As the federal government considers a ban on such products, Sobeys Inc. has unveiled a plan to phase out plastic bags from its locations and replace them with a paper bag option by the end of January.

But at least one professor isn't entirely convinced paper bags are the best alternative, as the material poses its own set of environmental challenges.

"I'm not so sure it's going to be a simple replacement of one single-use item made of plastic with another single-use item such as paper," Tony Walker, assistant professor at Dalhousie University’s School for Resource and Environmental Studies, told BNN Bloomberg Friday. 

"If you take a look at paper, there's the production – maybe the fertilizers and the insecticides used in forestry plantations – then there's the pulping process. In Canada, we have chemical craft pulp paper mills as well as mechanical pulping – both of which require huge amounts of energy. And then when the bag is actually manufactured, they're slightly heavier than plastic so it costs more to transport," he said. 

Contrast that with manufacturing plastic bags, which can have very little greenhouse gas emissions – something the plastics industry has been happy to tout. 

The story changes though when you consider the bags' after-life cycle, Walker says.

Plastic bags that end up in the environment can remain for hundreds of years, but break down into microplastics.

That's why if Walker had to take one side of the debate, it would be paper bags, he says. 

"Even though they would incur higher greenhouse gas emissions, they're either compostable if they're soiled and if they're not soiled, they can be put into paper recycling," he says. 

His top choice for consumers, though, would be reusable bags.

"The one with the least environmental footprint would be something like a hemp bag, but they're not commonplace unfortunately," he said.