You see, what we are fed by the likes of Al Gore is Global Warming LiteTM. Unfortunately, this dumbed down, Layman's terms version of Climate Change theory simplifies it into things that are easily challenged by skeptics.
Many people do have legitimate concerns about climate change, but unfortunately they are drowned out by the far more sinister motives of the polluting industries that stand to lose from climate change mitigation and fundamentalist Christians that have adopted the "Well, we might as well go out with a BANG!!" attitude.
Legitimate concerns include further research of our climate system and its various cycles and oscillations to see how they affect global temperature and precipitation, as well as studying our sun and try to figure out the cycles it goes through. Besides the ENSO, the oscillations which are now an integral part of long range forecasting are all relatively new. We don't know if they simply redistribute heat or if they could enter a phase where they trigger a snowball effect that pushes us into a much warmer or colder world.
One of the things that Gore has you believe is that global warming in the past 100 years is mostly due to human activities. That is simply not the case. It is hardly surprising, from a natural perspective, that the planet warmed during the 20th century. Our sun is more active now than it has been in 1000 years. Also, oscillations have lined up in a way that supported a strong warming trend in the past 30 years. We really do not know the impact that human activities has had on our climate thus far. We really have no accurate way to measure that. But that doesn't mean we're not affecting the climate enough for it to be noticeable.
Al Gore is a politician, and his main focus is on policy, not science. For that reason, he does not try to help you understand the science in order for you to become scientifically enlightened, but so you will vote for politicians that see Global Warming as a threat and will do something about it. Screaming "the sky is falling" and doing nothing at all (lest the economy be hurt... please, there are more important things hurting our economy, but we can discuss that somewhere else)... are both not options. There are plenty of very good reasons to reduce CO2 emissions outside of manmade global warming. We are turning our oceans into an acid bath which will have detrimental effects on many of the primary food sources of the oceans. Also, as we continue to pump Co2 into the atmosphere, the ocean's ability to absorb it will decrease, which will result in an increasingly fast increase in atmospheric concentrations, given constant emissions.