The problem here is mere existence is an externality, if you make the claim that government should have the power to curb externalties then the very idea of limited governance ceases to exist, as a government empowered to control externalities has unlimited power, as everything is an exernality include human breath.

Murder, or Dumping toxins is not on the same vein as CO2 emissions not even close, for former as a theoretical harm that may occur over 100+ years if technology and human behavior does not change naturally something not supported by history

Murder and Dumping toxins has a direct instant harm caused with immediate effect, if you can not see the difference then I am not sure how to continue the conversation