Tens of thousands of environmental protestors paraded through New York City on Sunday, in a "people's climate march" designed to lobby world leaders arriving for the latest United Nations climate summit. The march did succeed in messing up traffic, but President Obama won't achieve much more when he speaks Tuesday at this latest pit stop on the global warming grand prix.

Six years after the failure of the Copenhagen summit whose extravagant ambition was to secure a binding global treaty on carbon emissions, Mr. Obama...