The movement to ban straws is starting to swallow up whole countries. Canadian Prime Minister Justin Trudeau announced Monday that his Liberal government would ban plastic straws and other harmful single-use plastics as early as 2021.

"Canadians know first-hand the impacts of plastic pollution, and are tired of seeing their beaches, parks, streets, and shorelines littered with plastic waste," Trudeau said in a press release. "We owe it to our kids to keep the environment clean and safe for generations to come."

Few policy specifics were offered Monday. The government's press release mentions its intention to ban plastic straws, cutlery, and plastic bags, and to work with provincial and territorial governments to develop waste-reducing standards for plastic manufacturers.

Whatever specific action Trudeau's government does take, we're assured, "will be grounded in scientific evidence." But one statistic cited in Monday's press release is less than sound.

In a bullet-pointed list of "quick facts," there's a claim that Canadians throw away close to 57 million plastic straws a day. The same figure popped up in Vancouver, British Columbia's "Single-Use Item Reduction Strategy," published in May 2018. The city banned straws the same month.

A footnote in that report explains that this particular straw stat is derived from U.S. recycling company Ecocycle's estimate of American straw usage, which Ecocycle puts at 500 million straws a day. Assume the same per capita usage among Canadians and adjust for the country's smaller population, and you get 57 million straws a day.

That seems reasonable on the surface. The trouble is that the underlying 500 million figure was the product of a 2011 phone survey of straw manufacturers conducted by Milo Cress, who was then 9 years old.

Professional estimates of American straw usage vary, but they all put the number lower than 500 million straws a day.

The English-speaking world is particularly bad at straw math. Governments in the U.K. and Australia have relied on inaccurate and unsourced statistics on straw usage to justify bans. One could argue that one bad stat or two doesn't actually undermine the broader environmental change Trudeau and company are trying to achieve. But other numbers do.

According to a 2015 study, the U.S. is responsible for about 1 percent of annual marine plastic waste; the vast majority of such waste comes from East Asian countries. Canada's contribution to this admittedly serious problem is smaller still.

Banning plastic straws and plastic bags in the U.S. and particularly Canada will have a negligible effect on the world's oceans. Efforts to combat localized plastic litter, meanwhile, are best left to local governments, who hopefully can find less coercive means of cleaning up beaches and river banks.