Inside Climate: One of the most sensitive unresolved questions facing negotiators of a new global climate treaty is how binding it will be. If the treaty expected to be reached in Paris this year is without enforceable strict rules, some argue it will not be credible, while others say if nations are bound too rigidly, they won't agree to anything ambitious enough to matter. And the key to the whole conundrum is likely the United States. Behind the scenes, a consensus may be emerging that the treaty's only truly...