Does the Existence of Global Warming Matter?

This past week, I found myself engaged in a debate regarding the existence of climate change. To me, it was like debating if the sky is blue, but my opponent probably thought it was like debating the existence of Big Foot (not to be confused with the Yeti whom we all know exists). He proposed the following argument (which you may have heard on "insert conservative talk show name here"):

For the global warming alarmists to be right, all of the following three have to be true:

1. The globe is warming.
2. It is caused principally by human activity (not principally by natural cycles).
3. It will result in disaster.

Makes sense right? It follows logically and I would not necessarily disagree with the structure of the first two caveats of the argument. As I said above, I do believe the first two are true. The scientific consensus from every major scientific body backs those two claims. I do not believe that I am an expert in everything (contrary to what my wife may say about me), so I have to defer to those "in the know" (or at least to whom Wikipedia says is "in the know"). In regards to the third part of the argument, I would rewrite it as follows:

3. It will result in a net negative effect on humanity.

I think an important underlying premise of this rewritten third caveat that net negative effect does not necessarily only incorporate "bad things" happening to humanity, but also includes missing out on "good things" for humanity. Much in the same way that financial decisions look at net present value, it is important to look at the net present value of not taking action against climate change. If we miss out on returns by not taking action (e.g. renewable energy, sustainability movements, etc.), then those accrue as "negative cash flows" to humanity.

OK, I realize I was just a little over philosophical and nerdy, so to simplify my argument, I think you can simplify the argument to take action down to one question:

Is there a higher probability that EITHER climate change will result in a net negative effect on humanity OR taking action against climate change will result in a net positive effect on humanity?

Notice the relevant question is not if global warming or climate change or the great socialist conspiracy (feel free to pick your own name as well) actually exists, but whether not acting against climate change is the best option. Further, as we are dealing with imperfect information, we have to use our best judgment (via probabilities) with the data that is available. If we take the no-action approach, then we are simply rolling the dice and hoping nothing bad happens. However, if we take action against global warming, then the probabilities point to two positive outcomes, a cleaner and (more than likely) cooler world and a good start on energy independence.

If you are still not impressed, I came across this link on Twitter as I was posting this. The use of Pascal's Wager is an excellent premise (if you're into that sort of thing).