The problem with carbon taxes are the incentives to cheat. The US is probably being the 'most honest' by simply saying we won't implement them. In China and India they would simply misreport their emissions and not pay the tax. And of course, you can't hit the carbon targets w/out getting India & China on board.
In the absence of a world governing body with teeth (e.g. space aliens with a death ray), you can't enforce a carbon tax.
In the absence of a world governing body with teeth (e.g. space aliens with a death ray), you can't enforce a carbon tax.