This paper explores the epistemological basis for economic prognostications of climate change activists arising from, arguably, the most important scientific problem confronting modern society: the facts, beliefs and theories associated with the measurement, causes, impact and mitigation of climate change. This facilitates identification of the role that rhetoric plays in activist claims associated with the economics of global warming and climate change. Following a rudimentary discussion of ancient views on rhetoric, the connection of rhetoric with antifoundational epistemology and language is identified. Criteria for determining when language is rhetorical are specified. Exploiting this philosophical background, mitigation proposals of climate change activists derived from models of climate change economics are critiqued.