That isn't the hard law of the universe (the universe cares little about 'clean' or 'problem'). You can't put it back the way it was, but you may be able to put

That isn't the hard law of the universe (the universe cares little about 'clean' or 'problem'). You can't put it back the way it was, but you may be able to put it into a better position than it was before. Thermodynamics doesn't prevent carbon sequestration from working because the carbon dioxide is still carbon dioxide, not the hydrocarbons it was before (also there's a general presumption that even if you don't manage a cheaper sequestration than the original energy gained when producing it, you can still effectively 'pay back' some of the costs of fossil fuel generation with renewable generation, with interest).