The global warming thing is an attempt to get the attention of the newspapers and politicians, because if you don't make it simple and dramatic they ignore it. The real question is: Are the activities of humans having a possible irreversible effect on the planet, that could lead to the End of Life as We Know it?
You can think of the yeast in a bottle of grape juice, eating sugar and making CO2 and alcohol. Life is great until the alcohol concentration kills all the yeasts. Earth and the wine bottle are both closed finite systems.
As a geologist, the span of human history is hardly even within the resolution limits of the geologic record, and so is geologically insignificant.