Seattle's new ban on plastic grocery bags took effect yesterday and the question is "what will success look like?"

The immediate reaction might be that success means reducing the number of plastic bags used by consumers. The law is almost certain to do that, since the bags are banned and heavier plastic bags will cost 10 cents a bag.

That, however, is not the goal of the ordinance. During the debate about the ban, advocates pointed to the impact plastic bags had on Puget Sound and sea life. Although the impacts were speculative, relying on the "presence" of plastic in the water rather than actually demonstrating impact on sea life, if the ban is effective, the City should be able to demonstrate environmental improvement a year from now. If, however, there is no reduction in plastic in Puget Sound, the ban may actually do more harm than good to the environment.

The problem for the City is that the ban is likely to increase other types of environmental impact. The City's own analysis found that plastic bags use less energy than paper bags and, depending on the number of uses, reusable bags. That same research found that other types of bags use more water.

So, what does success look like? If there is a noticeable reduction in plastic in the water is that more important than an increase in energy use and carbon emissions? What if we don't see a reduction in plastic in the water? Will the City simply claim, as is the case with so many failed government policies, "it would have been even worse" without the ban? Of course, such a claim could not be verified and offers the political benefits of the policy without actually providing environmental benefits.

Based on past experience, it is unlikely the City will even attempt to measure the impact of the ban on the environment or set clear benchmarks. From "car free days," to green building standards and the City's pledge to meet the Kyoto Protocol's carbon emission targets, the City hasn't had much luck accurately predicting the results of their policies.

So, if Seattle doesn't actually check to see if they are achieving the environmental impact that was the justification for passing the ordinance in the first place, was environmental benefit the real goal? Or was the real purpose of the legislation to provide social and political benefits to the Councilmembers and supporters of the ban? The truth should be obvious in the near future.