I believe that man-made CO2 emissions likely have a significant impact on the climate, and we should do something about it, but even so the issue is a very complex one and its politicization hasn't helped. Here's why it's not so easy:

1. The data is crap. What you need is average temperatures and other data (humidity, pressure, cloud cover, albedo, etc.) over the entire Earth down to a fairly small scale. What we have is a mismash of horribly calibrated weather station data near cities combined with limited satellite data and various proxies, all of which has to be massaged a great deal to make it usable. Sea level data has the same sort of problems, nearly impossible to properly calibrate to sufficient precision. The fact that people have poured tons of effort into collecting and attempting to calibrate data doesn't mean the data is actually very good.

2. The models are also crap. A century ago Svante Arrhenius came up with the greenhouse effect theory and did some back of the envelope calculations on its magnitude, coming up with a figure of climate sensitivity of about 2 deg. C per CO2 doubling. Today all of our vaunted climate modelling hasn't managed to come up with a more accurate figure than that. Current estimates are still "maybe 2 deg. C per doubling, with some enormous error bars". Modern models have several problems. The conceit is that climate models are de novo elaborations from first principles and are as rock solid as our understanding of the laws of physics. In practice all climate models contain multiple "empirically determined" fudge factors. They fit the data, they don't predict it. And that's assuming we even had enough good data to really run good prediction checks, which is dubious at best.

3. The climatology scientific community is very problematic. There is little indication of sufficient rigor, and criticizing results is an easy way to get effectively excommunicated from the community. Take, for example, the famed "hockey stick" paper, which has now been thoroughly discredited, but all of the discrediting happened effectively "behind the scenes" and quietly. Science works best when it's open and boisterous. It's surprising that climatology isn't in even worse state given how insular and political it is.

4. Even if we assumed that man-made carbon emissions were going to cause a huge degree of global warming there is still a huge gap between that fact and figuring out what to do about it, which many folks simply skip over. The actual damage (to the biosphere and to human activities) is just as difficult to determine as the climate is to predict. The right course of action to take depends a great deal on lots of different factors: sociological, technological, and economic. Especially since a lot of the CO2 production of the 21st century will come from economies that are climbing out of poverty and into affluence. It may well be the smartest choice to simply continue polluting until the world is richer and more technologically advanced and then consider mitigation strategies.

4a. CO2 emissions may not be, and likely is not, the most important pollution issue everywhere in the world currently. But it gets the most attention and sometimes that makes it more difficult to get traction on other issues.

Meanwhile, there really are serious "climate change denialists" and some of the folks on that side are absolutely terrible. Canadian PM Harper banned government scientists from talking to the press, for example. But the answer to science being perverted for political reasons isn't to simply pervert it in the opposite direction to compensate.

It's just a complete shit-show across the board and I'm not happy with how any of it is being handled at either the level of scientific inquiry or public policy.