Both the citation of projected GDP increase as a justification for UBI and the use of carbon taxes to fund it strike me as wrongheaded.
GDP is a poorly defined quantity with only a loose relationship to the more relevant factor of median wellbeing; and, depending on how it is defined, it may either increase or decrease as a result of UBI. So I would be most reluctant to suggest that support for a UBI should be conditional on how it is perceived to affect GDP – especially as some alleged experimental trials have claimed to produce a negligible or even negative effect.
And with regard to revenue from a carbon “tax” I think it should be devoted entirely to the funding of prevention and mitigation of adverse effects from anthropogenic climate change.
The appropriate justification for providing an unconditional basic income is the fact that we all share ancestry with the initiators and creators of most current human wealth and of the intellectual and physical capital that enables the scale of its current rate of increase. And by the same rationale, its funding should come from a tax on the highest levels of wealth and income – including especially the unearned income that results from large gifts and inheritances.
Source: Basic income could solve global poverty and stop environmental destruction, study finds – Beyond