While there is evidence that the planet is warming, ever so slightly (ice core samples for example), I agree the cause is what is in question.

Another tidbit they don't tell you is that if you look at global temperatures historically, the planet warms and cools in roughly 100-thousand year cycles. We are currently on a warming trend, just recovering from a "little ice age" that started at the end of the Midievel period (1300-1400AD). ( data source )

What's interesting here and is up for debate is the RATE of warming during the current period. While some will argue that the rate is beyond what should be expected due to man's interference, the question then becomes is the rate just indicative of better analysis of the data? So the rate is also in question.

What bothers me even more about this whole question is the very idea that humans are big enough to mess with Gaia. That is absurd and very arrogant and quite frankly, as stated, we're a mere virus that can (and may be someday) overcome by Gaia.

-G