First, I believe that CO2 (among other gases) is increasing in the atmosphere due to human activity, and that this will have a first order effect of warming the planet. I also believe that we have seen moderate warming over the last century or so (indeed the warming started even before the CO2 really took off). But I don't believe that the evidence for predictions of large, catastrophic global warming is, as we are often told, "unequivocal." Here's how I know.
In 2009 I saw global warming alarmists on the internet gleefully pointing out this new study from MIT scientists, showing that "climate change could be double previous estimates. " Here's a quiz: should this make you more or less confident in global warming models? I'd say that if you just found that your previously unequivocal models might be off by a factor of 100%, you might want to rethink whether they are really so unequivocal or not. If they can be 3 degrees too low, maybe they can also be 3 degrees too high. (This isn't unique: here's something from 2005 predicting warming twice as bad as previously thought.) Instead, findings like this seem to only make climate alarmists more sure of themselves. And people were already saying these predictions were unequivocal back in 1996 when they didn't even know about something so important as the Pacific decadal oscillation yet.
I mean, these models are really, really complicated. They have lots of degrees of freedom. And I don't believe they have produced any very impressive out-of-sample predictions yet. Furthermore, I'm confident that all the funding and publication biases would run in the direction of people wanting to predict more warming. Scientists are unfortunately not immune to overconfidence and confirmation bias.
And when I read criticism of "deniers" and "skeptics," all the focus seems to be on the least informed straw man arguments that come from people like Rush Limbaugh. I never see anyone respond to skeptics like this guy.
So I don't discount the possibility that CO2 emissions might have large impact on climate. I think it is definitely something to worry about and study. Climate science is not a "scam," as many crazies on the right will tell you. But being told it is unequivocal really gets my BS detector going. Apparently expressing any skepticism about even the magnitude of effects is enough to get you kicked out of polite society. This is not healthy.