Nearly 200 nations signed the Paris accord to tackle climate change – but signing isn’t implementing, critics say. The deal sets out to commit signatories to reduce carbon emissions, but the targets are not legally binding. And that worries those who don’t trust big polluters, like China and India, to act. Even its most ardent supporters aren’t dismissing inherent flaws. Top US negotiator Secretary of State John Kerry acknowledged this in an appearance on ABC News a day after the deal was announced Saturday. “I understand the criticisms of the agreement because it doesn’t have a mandatory scheme and it doesn’t have a compliance enforcement mechanism…. That’s true.” The other worry for detractors is that because the agreement is not a “treaty,” US congressional approval is not mandatory for ratification. Optimists point out that, while imperfect, the pact is a serious beginning, evidence that the world is no longer ignoring that which cannot be ignored.