Like cigarettes, plastic bags have recently gone from a tolerated nuisance to a widely despised and discouraged vice.

Last month, the New York City Council passed a 5-cent-per-bag fee on single-use bags handed out by most retailers. Last week, the Massachusetts State Senate passed a measure that would ban plastic bags from being dispensed by many retail businesses and require a charge of 10 cents or more for a recycled paper or reusable bag. The Massachusetts proposal may not become law this year, but it’s the latest sign that the plastic bag industry is losing this war. Already in Massachusetts, 32 towns and cities have passed bag bans or fees. So have at least 88 localities in California, including the cities of Los Angeles and San Francisco, plus cities and towns in more than a dozen other states and more than a dozen other countries.

The adverse impacts of plastic bags are undeniable: When they’re not piling up in landfills, they’re blocking storm drains, littering streets, getting stuck in trees, and contaminating oceans, where fish, seabirds, and other marine animals eat them or get tangled up in them. As longtime plastic bag adversary Ian Frazier recently reported in The New Yorker, “In 2014, plastic grocery bags were the seventh most common item collected during the Ocean Conservancy’s International Coastal Cleanup, behind smaller debris such as cigarette butts, plastic straws, and bottle caps.” The New York City Sanitation Department collects more than 1,700 tons of single-use carry-out bags every week, and has to spend $12.5 million a year to dispose of them.

Bag bans cut this litter off at the source: In San Jose, Calif., a plastic bag ban led to an 89 percent reduction in the number of plastic bags winding up in the city’s storm drains. Fees have a smaller, but still significant, effect. Washington, D.C.’s government estimates that its 5-cent bag tax has led to a 60 percent reduction in the number of these bags being used, although that figure is contested by other sources.

Is plastic really worse than paper?

But advocates of these laws and journalists who cover the issue often neglect to ask what will replace plastic bags and what the environmental impact of that replacement will be. People still need bags to bring home their groceries. And the most common substitute, paper bags, may be just as bad or worse, depending on the environmental problem you’re most concerned about.

That’s leading to a split in the anti-bag movement. Some bills, like in Massachusetts, try to reduce the use of paper bags as well as plastic, but still favor paper. Others, like in New York City, treat all single-use bags equally. Even then, the question remains as to whether single-use bags are necessarily always worse than reusable ones.

Studies of bags’ environmental impacts over their life cycle have reached widely varying conclusions. Some are funded by plastic industry groups, like the ironically named American Progressive Bag Alliance. Even studies conducted with the purest of intentions depend on any number of assumptions. How many plastic bags are replaced by one cotton tote bag? If a plastic bag is reused in the home as the garbage bag in a bathroom waste bin, does that reduce its footprint by eliminating the need for another small plastic garbage bag?

If your chief concern is climate change, things get even muddier. One of the most comprehensive research papers on the environmental impact of bags, published in 2007 by an Australian state government agency, found that paper bags have a higher carbon footprint than plastic. That’s primarily because more energy is required to produce and transport paper bags.

“People look at [paper] and say it’s degradable, therefore it’s much better for the environment, but it’s not in terms of climate change impact,” says David Tyler, a professor of chemistry at the University of Oregon who has examined the research on the environmental impact of bag use. The reasons for paper’s higher carbon footprint are complex, but can mostly be understood as stemming from the fact that paper bags are much thicker than plastic bags. “Very broadly, carbon footprints are proportional to mass of an object,” says Tyler. For example, because paper bags take up so much more space, more trucks are needed to ship paper bags to a store than to ship plastic bags.

Looking beyond climate change

Still, many environmentalists argue that plastic is worse than paper. Climate change, they say, isn’t the only form of environmental degradation to worry about. “Paper does have its own environmental consequences in terms of how much energy it takes to generate,” acknowledges Emily Norton, director of the Massachusetts Sierra Club. “The big difference is that paper does biodegrade eventually. Plastic is a toxin that stays in the environment, marine animals ingest it, and it enters their bodies and then ours.”

Some social justice activists who work in low-income urban neighborhoods or communities of color also argue that plastic bags are a particular scourge. “A lot of the waste ends up in our communities,” says Elizabeth Yeampierre, executive director of UPROSE, an environmental and social justice-oriented community organization in Brooklyn. “Plastic bags not only destroy the physical infrastructure,” she says, referring to the way they clog up storm drains and other systems, “they contribute to emissions.” And she points out that marine plastic pollution is a threat to low-income people who fish for their dinner: “So many frontline communities depend on food coming from the ocean.” That’s why her group supported New York City’s bag fee even though it’s more of a burden on lower-income citizens. A single mom, or someone working two jobs, is more likely to have to do her shopping in a rush on the way home from work than to go out specifically with a tote bag in hand. But for UPROSE, that concern is outweighed by the negative impacts of plastic bags on disadvantaged communities.

Increasingly, environmentalists are pushing for laws that include fees for all single-use bags, and that require paper bags to be made with recycled content, which could lower their carbon footprint. The measure now under consideration in Massachusetts, for example, would mandate that single-use paper bags contain at least 40 percent recycled fiber. That’s the percentage the Massachusetts Sierra Club has advocated for at the state level and when lobbying for municipal bag rules.

It’s complicated

But what if reusable bags aren’t good either? As the Australian study noted, a cotton bag has major environmental impacts of its own. Only 2.4 percent of the world’s cropland is planted with cotton, yet it accounts for 24 percent of the global market for insecticides and 11 percent for pesticides, the World Wildlife Fund reports. A pound of cotton requires more than 5,000 gallons of water on average, a thirst far greater than that of any vegetable and even most meats. And cotton, unlike paper, is not currently recycled in most places.

The Australian study concluded that the best option appears to be a reusable bag, but one made from recycled plastic, not cotton. “A substantial shift to more durable bags would deliver environmental gains through reductions in greenhouse gases, energy and water use, resource depletion and litter,” the study concluded. “The shift from one single-use bag to another single-use bag may improve one environmental outcome, but be offset by another environmental impact.”

But studies conducted in Australia or Europe have limited applicability in the U.S., particularly when you’re considering climate impact, because every country has a different energy mix. In fact, every region of the U.S. has a different energy mix.

“There’s no easy answer,” says Eric Goldstein, New York City environment director for the Natural Resources Defense Council, which backed NYC’s bag fee. “There are so very many variables. Here’s just one tiny example: Does the paper for paper bags come from a recycled paper mill on Staten Island or a virgin forest in northern Canada? As far as I know, nobody has done the definitive analysis, which would necessarily need to have a large number of caveats and qualifications. Also, this question is something like asking, ‘Would you prefer to get a parking ticket or a tax assessment?’ It depends on the specifics, but it’s better to avoid both wherever possible.” Goldstein is confident that if people switch to reusable bags, even cotton ones, and use them consistently, that will ultimately be better for the environment.

The ideal city bag policy would probably involve charging for paper and plastic single-use bags, as New York City has decided to do, while giving out reusable recycled-plastic bags to those who need them, especially to low-income communities and seniors. (The crunchy rich should already have more than enough tote bags from PBS and Whole Foods.)

The larger takeaway is that no bag is free of environmental impact, whether that’s contributing to climate change, ocean pollution, water scarcity, or pesticide use. The instinct to favor reusable bags springs from an understandable urge to reduce our chronic overconsumption, but the bags we use are not the big problem.

“Eat one less meat dish a week — that’s what will have a real impact on the environment,” says Tyler. “It’s what we put in the bag at the grocery store that really matters.”