There's some discussion about global warming going on in another post. So, what harm could a small post by me do, except for increasing the spam in my blog's mailbox :)
The main reason that I believe that global warming, which can be influenced by humanity, is not a hoax, is that 194 countries including traditionally "selfish" ones like China, Russia and India are part of these climate conferences. Sure, progress is terrible as is to be exspected considering that they have to deal with the mother of all Free Rider problems.
But don't look so much at what is being written and more at was is being done. If so many countries accept high costs to do something, there's something to it in my opinion. I don't think the European Union would unanimously give away billions of dollars if it were a hoax.
To a degree, you can also try to look at the science yourself. That more CO2 causes heating is pretty obvious. It's even easy to see in very simple experiments. You can do these things yourself at home, actually. Alternatively you can do a youtube search for "greenhouse effect experiment".
It's also a pretty good explanation for why other planets, like Venus, are as warm as they are. At least I favor this explanation to aliens having installed heaters there :)
I guess the only thing about global warming which is uncertain is what the exact effects will be. But since 194 countries on the planet - irrespective of their current governments - seem to think that the consequences could be a real problem - so do I.
Honestly, the only people I know who don't believe in global warming are right-leaning US-Americans. And they have a good excuse: they have an active and well founded press in their country that understands that the more controversial a topic the higher the profit. Still, right-leaning Americans are a very tiny global minority.
So, sorry Goodmongo, but I think the reasons to believe in global warming are overwhelming. And I say "believe" on purpose. Only in the church do people believe to know something. Outside the Church we all know that we can only believe.
Final sentence: there are many scientists who lie and cheat to make the countries do something against global warming. They are stupid and should know better.