Is anyone actually debating whether GW (or, more generally, global climate change - temp, sea level, ice, precip changes, ocean SSTs, etc) is occurring anymore? This is AMPLE evidence that global warming is happening. That's not the debate.
Why would Al Gore debate someone? HE'S NOT A SCIENTIST! He's a politician who has taken up a cause. In the process, like most politicians, he's polarized entire populations, many who reach their "conclusion" based solely on what they think could or could not happen, regardless of any physical evidence to support such a belief. The global climate change (since we should include not only temperature changes, but also sea level, ice, precipitation, ocean temperatures and salinity, etc., changes) issue has turned into a blue vs. red issue - i.e. it has turned into a political issue. To some degree, this is expected, since political policy has been brought into the global warming arena. However, it has dumbed down the populace as people listen to their favorite talk radio host, one who doesn't have any idea about the science behind climate change, to form their own opinion. Rather, I should say, they just take the "opinion" of their favored talk show host. Yes, this goes both ways, both the "OMG The world will be aflame tomorrow!" crowd and the "global warming is a crock of garbage" crowd. Interestingly, it seems as though it's becoming increasingly trendy to join the "pff, global warming is scam" crowd. There has been a misrepresentation of the science by both sides, and it doesn't take much of a Google search to find such rampant misreprentations... Example: big story run by some about how the ice in the N. Hemi. has grown at a record rate this fall. Well, it has, but it's growing from a near RECORD LOW, and a look at the trends certainly tells a story much different from the "ice growing at record pace - GW is crap!" false conclusion.
I'm not necessarily saying the global warming is completely and certainly being caused by human activity, and many scientists would agree that anthropogenic forcings are not 100% certain. However, there seems to be considerable more evidence to support it than to refute it. Are humans causing it? Again, there is some evidence to support such a notion. Yes, the world HAS been warmer in the past without humans. There are plenty of NATURAL forcings that can cause global climate change. However, just because it's happened naturally in the past does NOT mean that it CAN'T happen any other way! You cannot draw that conclusion. The world may well be warming without humans, but it's the RATE at which the warming has increased in the past 100 years that is anomalous. As such, the evidence would seem to support the idea that it's certainly POSSIBLE that humans can affect the climate. The residence times of some greenhouse gases is on the order of centuries and millenia!
As with many issues, the truth probably lies between the two extremes... The Earth likely will not become engulfed in flames tomorrow (nor will sea level rise 30 feet by 2010), but it also seems likely to me that the observed climate change (temp, sea levle, ice extent, etc) is being enhanced by human activity (greenhouse gas release, deforestation, land use changes, etc). Just because the messanger may have an agenda does not mean that the entirety of the message is false.
FWIW: Are these 30,000 folks the same economists, sociologists, and TV "meteorologists" who signed the petition to Congress? Heck, that list included many actual scientists who merely stated that it was NOT certain that humans were causing global warming. There are examples on that list of scientists who have said that GW may or may not be significantly affected by humans, and those folks were counted as being "against" the idea of anthropogenic GW by the makers of that list. *rolls eyes* Yes, there are legitimate climate scientists who do not believe humans are having any effect on climate, and,heck, it's good that there is disagreement. In the end, it will be for the betterment of climate science that doubt exists. However, misrepresentation and politicalization of the science only misleads people and undermines the science.