We are talking about temperature patterns on a geologic (solar?) timescale here. the explosion in the human population has happend over the last century.
Best we can tell from ice cores, tree rings, etc is that the current warming trend is happening about an order of magnitude faster than prior trends. The only question is whether it is natural or caused by human activity. Satellite readings of the amount of heat radiated back into space have fallen (measurements have been taken since 1970, I believe), specifically in the band corresponding to CO2. Atmospheric CO2 levels have surely been higher in the distant past, but again, so far the data indicates that the levels have never risen nearly as fast as today.
Do I think anybody can be 100% certain, today, that humans are causing a warming trend that will have catastrophic consequences? Nope. Am I glad that resources are being devoted to studying it further, that models are being improved, and that if human activity is ultimately deemed to be the cause, that we might be able to mitigate the damage for future generations? Hell yes.