It is possible that the Portland city council made a devil's choice with its ordinance banning plastic bags in favor of cloth or paper bags.
In the pursuit of sustainability - plastic bags have been given "Eco-Demon" status...paper and cloth are now icons...but Oregon chemistry professor David Tyler explains why that's not necessarily true. 
"If you do what is called a life cycle assessment it turns out plastic bags are really good compared to paper bags or even re-usable tote bags in terms of greenhouse gas production during the lifecycle of the bag are far less than a paper bag or a reusable tote bag".
Of course - he adds - plastic bags are forever - no biodegradability.  Still, it's a matter of pick your eco-poison.
Tyler teaches a sustainability class at the U of O.