As far as the scientific study of current climate goes, that's essentially been proven. The arguments from global warming skeptics are now more focused on the amount of warming that will occur in this century, not IF warming will occur in this century. The position of the informed global warming skeptics is that the warming in this century will tend toward the minimum change indicated by climate models.
Nonsense. Where's the baseline?
Perhaps. But the causality has not! The data strongly suggest that global warming (and cooling) are very long-period cycles controlled by forces far outside the control of man.
Repeat after me:
Man-made Global Warming is a MYTH!
Man-made Global Warming is a MYTH!
Man-made Global Warming is a MYTH!
The global warming that we can now measure is not directly attributable to anthropogenic forces alone; the need to use fuels efficiently will lead to more CO2 per energy unit and a wiser move would be to create more carbon sinks.