Actually, I'd argue that "we're not causing warming" is very much a positive claim. When the fundamental physics of CO2, methane and water say they must trap heat by absorbing infrared radiation, and that therefore adding substantial amounts of the non-precipitable species (CO2 and methane) must cause warming... well, if you're saying it's not happening you're either saying that fundamental physics is wrong, or you're effectively positing some other mechanism to keep temperatures down. Either is a positive claim in need of evidential support.
