Quite simply, anybody who points to the current heat waves in various places as "proof" of Global Marming doesn't even understand their own hyposthesis and may be dimsissed with a wave of the hand.
The hypothesis is that the globe is warming up very slowly -- a small percentage of a degree per year and that it is a slow trend. So you don't even have to deal with the preposterous notion of whether it is human-accellerated (I think they are finally coming around to agreeing it is part of the planetary cycle).
True. On the other hand, I believe there is quite conclusive proof of global warming. Over the past thirty years there is statistically significant photographic evidence that the polar ice caps have reduced in size. That is, the CO2 ice caps on Mars.