This claim relies on an pedantic definition of "causes". The biggest direct cause of global warming is water vapor. However, the main thing affecting water vapo

This claim relies on an pedantic definition of "causes". The biggest direct cause of global warming is water vapor. However, the main thing affecting water vapor concentration is other greenhouse gases. Therefore the root cause is other greenhouse gases, the most important of which is CO2. Water vapor simply acts as a multiplier to the effect of these other gases.