Humans are vigorously adding to the CO2 content in the atmosphere, right? According to this chart, total human contributions to greenhouse gases account for only about 0.28% of total greenhouse gases.
Approximately 99.72% of the "greenhouse effect" is due to natural causes -- mostly water vapor and traces of other gases, which we can do nothing at all about. Eliminating human activity altogether would have little impact on the quantity of gases supposedly linked to climate change. - link