A very early-draft stage proposal for a new web file verification system. Basically, you add a carbon.txt file to your site specifying where the site is hosted. Hosts would then provide a file stating where their data centres are. Those, in turn, state where the energy is coming from. Energy providers can do the same, though that data is publicly available anyway in most European countries. So by following the carbon.txt chain, you can verify whether a site genuinely runs on green energy or not.