In public policy, this principle is too often forgotten or ignored. From education reform to the
War on Poverty, some seem happy to support policies based on emotions, not evidence.
The latest example is the plastic bag ban.
“Across the country, cities are joining the latest environmental trend — banning plastic grocery bags,” writes Todd Myers of the Washington Policy Center. “Concerned about the amount of plastic that reaches our oceans and the impact on wildlife, communities have decided that banning the bags is a simple and environmentally responsible approach. But is it? What does the science say?”
What’s significant is what science doesn’t say. It doesn’t say what many environmental groups contend.
“The evidence points to the fact that banning the bags may actually be a net negative for the environment, yielding little benefit to wildlife while significantly increasing carbon emissions and other environmental impacts,” Myers reports. “Advocates of banning plastic grocery bags often cite impacts on marine life and mammals, but they rarely attempt to quantify that impact.”
He cites the “Great Pacific Garbage Patch,” an area purported to be twice the size of Texas, that is filled with bags and other plastics. It’s nowhere near that big. One oceanographer warned, “There is no doubt that the amount of plastic in the world’s oceans is troubling, but this kind of exaggeration undermines the credibility of scientists.”
“When determining the environmental costs and benefits, however, we need to be honest about the science,” Myers says. “Indeed, there are risks from banning plastic grocery bags.
The most significant environmental risk from banning plastic bags is the increase in energy use. Plastic bags are the most energy-efficient form of grocery bag.”
Wait. What? They’re better than the canvas bags we feel so good about using?
“The U.K. Environment Agency compared energy use for plastic, paper and re-usable bags,” he reports. “It found the ‘global warming potential’ of plastic grocery bags is one-fourth that of paper bags and 1/173rd that of a reusable cotton bag. In other words, consumers would have to use a reusable cotton bag 173 times before they broke even from an energy standpoint.”
And there are other, indirect impacts to consider.
“It should be noted that the benefit of banning plastic bags is mitigated by the fact that half of the bags are used for other purposes, like for garbage bags or for picking up after pets,” Myers adds. “Grocery shoppers will still have to buy other bags, likely plastic, for those
“Communities need to sincerely weigh these various environmental costs,” he says. “Unfortunately, few do any analysis because the political symbolism of banning the bags is powerful. It is often easier to ignore the science that indicates such bans may actually harm the environment than make an honest effort to weigh these difficult issues.”
This mindset — weighing intentions over evidence — complicates our lives and, inarguably, makes them more difficult. Why do we see so many devastating forest fires during the summer? Because we like trees. We frown on logging and even controlled burns. The result? We have fewer trees, because fires can’t be contained as quickly.
We should honor good intentions, of course. But they’re not enough. And we know, on good authority, where they lead.