With "enormous amounts of proof" it should be easy to provide a starting point.

Say something like this:
Assuming climate change  is happening (increasing CO2 causing global warming), due to recent human activity (post 1977), then one would expect to observe sea level rise rate increasing. You know, increased global temperature would result in more melting of ice sheets, plus water expands when heated bit. Yet looking at the global sea level over the past 100+ years, sea level rise has been quite constant.

http://www.climate4you.com/images/Holgate-9_Since1900-NEW.gif

So actual observed data would indicate, no abnormal sea level rise rate, hence one could provide a argument that human influence in CO2 heating the planet is NOT a significant factor.

Your turn.