Insufferable people only like saving the planet if it means they get credit from strangers.When Seattle voters rejected a plastic bag tax in 2009, supporters wondered what could have been. Now they don’t have to wonder anymore:Washington DC’s 5 cent tax on plastic bags, instated just this past January, has already proven to have a phenomenal impact: the number of plastic bags handed out by supermarkets and other establishments dropped from the 2009 monthly average of 22.5 million to just 3 million in January. While significantly reducing plastic waste, the tax simultaneously generated $150,000 in revenue, which will be used to clean up the Anacostia River.Seattle’s tax, as you’ll remember, was a bit more ambitious: 20-cents on every bag, whether paper or plastic. So we’re kind of comparing apples to oranges here. (Both of which, it should be noted, carry just as easy in a reusable tote.)D.C.’s ban is also brand new. So while the initial sting of that added nickel may be swaying consumers’ choices now, things might change in the next few months when everyone goes back to forgetting there’s an extra cost associated with convenience.Still, as some have already pointed out, the remarkable numbers coming out of D.C. should be a reminder to other cities like Seattle that have tried, and failed, to pass a tax in the past: aim a little lower and you might just hit your mark.