At the risk of being harsh, that video is a propaganda piece. Admittedly, so is "An Inconvenient Truth." From my limited understanding of climate science, although Al Gore takes some liberties (e.g. the complaint that CO2 is invisible so showing smokestacks venting smoke or steam is technically incorrect) his presentation meshes fairly well with what a large number of climate scientists believe. But really, the main point is that this should not be a popularity contest: public policy on issues like this should be decided by a combination of scientific consensus and risk analysis. There is certainly some uncertainly in exactly what is going on in the field, and some people make some interesting arguments about how to interpret and predict based on the measurements (Freeman Dyson, for example.) However, the uncertainty doesn't necessarily imply that the best course of action is to assume "until I see proof beyond all doubt, we should stay the course." There is relatively undisputed evidence that since the industrial revolution, human activity has had an impact on the atmosphere. Since we have never seen the effect of human activity on the earth like this before, we are in unexplored territory. As it happens, human beings are very happy in the global environment that's existed for the past few million years; there have been plenty of times in the history of the earth where human life wouldn't be possible at all because of the atmospheric makeup.
Just to dissect an element of the video that I think I can safely call out, though: the fact that water vapor is a more important greenhouse gas in the instantaneous effect has almost nothing to do with the argument made. The amount of water vapor in the atmosphere fluctuates on a fundamentally different timescale than CO2, since water tends to do things like fall out of the sky as snow or rain, and be renewed by evaporation. CO2, on the other hand, has a relatively slow half-life. Also, the water vapor cycle has been more-or-less in balance since the last ice age, but a small amount (e.g. 5-10%) change in the greenhouse gas levels from CO2 or water vapor could change that balance, since if the CO2 was enough to raise the ambient temperature, it's possible that this would cause more evaporation, leading to higher water vapor levels in the atmosphere, leading to more greenhouse effect from that, in a snowball effect (also, more dissolved CO2 could be released from the ocean into the atmosphere, and the albedo of the earth could be reduced by melting snow revealing darker material under it.) The video's "alternative explanation" of the greenhouse effect is an even more gross oversimplification than Al Gore's, since it shows 100% of incoming sunlight reflecting, rather than some being absorbed by the ground and oceans, which is misleading.
Certainly, it's a fair argument that we don't fully understand all of the things going on. However, from a "what's a good idea" standpoint, the atmosphere and albedo and vegetation biomass and outgassing of sequestered carbon from fossil fuels as CO2 are causing many of the driving forces to diverge further and further from the way things have been for the entire time that the planet has been well-suited to human life. Since we don't have complete information, it seems to me that the wisest course of action is to avoid straying into unknown territory that has an unknown risk of changing the biosphere in substantial ways, since, really, we're pretty much in the best possible place for our comfort and survival where we are, so any change that happens is likely to be bad news for the human race, and probably most mammals. The silver lining is that cephalopods have proven that they can survive through far more drastic changes in atmospheric oxygen and CO2 levels (and asteroid/comet strikes, and volcanic activity) so perhaps if we screw things up badly enough we'll open up an opportunity for the cephalopods archaeologists of the future to be amused at our peculiar primate technologies and curious artworks. Still, I'd sort of like to err on the side of caution for the immediate future.
As an unrelated criticism, I've never heard of "the heartland institute" as a scientific center, and about half of the talking heads in that seem to have dubious credentials. There's one MIT guy, what, two profs from Alabama and Ottawa, one National Weather Service guy, and a few of people with credentials that sound like "professional expert from the made-up-institute of we-know-how-to-sound-smart." I know a fair number of geologists, atmospheric chemists, environmental engineers, planetary scientists, astronomers, NASA scientists, marine scientists, and so forth, and I don't know any who express the sort of view expressed in the "heartland" video, and quite a few who think that Al Gore's version is oversimplified but gets the big picture close to rights. An exception to this is Freeman Dyson (who I have met briefly, but I doubt he'd remember me) who is somewhat skeptical, but more that people are too negative about things we might be able to do to avert disaster than that we should avoid doing anything. You might argue that I know a bunch of hippie-dippy ivory tower liberal intellectuals, but they're also some of the best and brightest of American science, and the qualified scientists appear to be about 90-99% in agreement with the Al Gore version than the "heartland institute" version.
A few interesting links:
Heartland Institute - SourceWatch
BBC NEWS | Special Reports | 629 | 629 | Climate scepticism: The top 10
http://gristmill.grist.org/skeptics
Edge: HERETICAL THOUGHTS ABOUT SCIENCE AND SOCIETY By Freeman Dyson
(I also recommend Peter Ward's book
Out of Thin Air which is only indirectly about the dynamics of atmospheric composition, but which I found very intriguing in its description of the historical dance between oxygen and CO2 levels, temperature, and life on earth.)
and I want to single out this one particularly:
http://www.sciencemag.org/cgi/content/full/306/5702/1686
because Science is the premiere journal published in the United States ( Nature is published in the UK, and is of similar stature) for representation of the academic consensus of professional scientists on any topic related to scientific inquiry. They don't tend to shy away from legitimate scientific controversy, and they put a great deal of effort into avoiding dishonesty, misrepresentation, and inaccuracy. In studying almost 1000 papers on this topic published in the forums in which real professional scientists stake their reputations and report their lives' work, there were
no publications whatsoever that argued against the scientific consensus as defined in that article.
I don't exactly mean this to be an attack: I'm glad that you're thinking for yourself, and I encourage you to learn as much as you can and decide for yourself. I find both the "heartland" video and "An Inconvenient Truth" to be oversimplified, misleading, alarmist, unscientific, and silly, and I think it's pathetic that we're making public policy decisions on the shallow propaganda version of this. And, I know how you feel, since my dad has been involved in the defense industry, and often gets frustrated when reality in that area is misrepresented by snooty academics. I trust and respect my dad, and enjoy having intelligent discussions on what he believes and why, and get irritated when I run into people who make simple-minded arguments that I believe are justified more by knee-jerk political views than objective reality, so emotionally I can very much relate to where you're coming from...
I don't expect you or anyone to automatically agree with what I say, so I hope that this is taken as an attempt to help you discover new information and consider why I might have the viewpoint that I have, and that perhaps I and others who share that have put some effort into having an informed opinion.