Responding to Sam Roggeveen's post and the question he poses to me: I think the best way to increase the costs to North Korea of its present course of action (and not only over the last weeks but years) is for affected parties to put pressure on the PRC for its support of North Korea through persuasion and by more public criticism of the PRC for its support of the DPRK.
This would not require escalation to military action against North Korea and would be a good addition to all of these affected parties' own China policies. China is the state that provides North Korea the most support for its present course of action and has the most capacity to increase the costs for North Korea short of military action. For me, the key is a change of behaviour in China and secondly a change of behaviour towards China of those countries affected by North Korean belligerence.
Photo by Flickr user Joseph A Ferris III.