Several philosophers and economists connect left-libertarian ideas with support for UBI. Of these, the most closely related theory to Georgism calls for a citizen's dividend—that is, a UBI equal to the monetary rental value of natural resources and socially created wealth. Writers advocating citizen's dividends include Peter Barnes (author of "With Liberty and Dividends for All"), economist Nic Tideman and activist Jeff Smith. Barnes proposes setting up a public "Sky Trust" to manage the funds creating from taxing pollution, greenhouse gases and other actions that deplete the value of shared natural resources.