The cause of my original beliefs on climate change is my parents' politics.
In my larval form, I had many more common misconceptions about how the greenhouse effect was supposed to work. The most wrong, and also the only one that I actually changed because of an anti' web site, was that the cycle of historical CO2 was a cause of historical climate changes, rather than an effect. Otherwise, I learned much more from RealClimate than I did the antis.
There was a distinct moment when I figured out that global warming was a physics problem that I could actually understand simple models of. Without these simple models, I would not actually understand the physical mechanism behind global warming. Most people still don't - people arguing on both sides don't know what they're arguing for/against.
The experts are basically right.
Note: Please see this post of mine for more on the project, my sources, and potential sources for bias.
I have written a couple of blog posts on my understanding of climate forecasting, climate change, and the Anthropogenic Global Warming (AGW) hypothesis (here and here). I also laid down the sources I was using to inform myself here.
I think one question that a number of readers may have had is: given my lack of knowledge (and unwillingness to undertake extensive study) of the subject, why am I investigating it at all, rather than relying on the expert consensus, as documented by the IPCC that, even if we're not sure is correct, is still the best bet humanity has for getting things right? I intend to elaborate on the reasons for taking a closer look at the matter, while still refraining from making the study of atmospheric science a full-time goal, in a future post.
Right now, I'm curious to hear how you formed your views on climate change. In particular, I'm interested in answers to questions such as these (not necessarily answers to all of them, or even to only these questions).