It is absolutely a belief. A theory. It is not necessarily correct, given that warm periods have occurred in the past. And I haven't ignored it. The discussion didn't begin when you arrived, you know. But I will indulge you for your own edification.
Three percent of CO2 emissions are attributable to humans. Three percent.
CO2 concentration only began rising markedly after 1950. Therefore you must agree, according to your beliefs, that warming between the Little Ice Age and 1950 was natural, and warming since 1950 man-made. Think about that for a bit.
There are no human fingerprints of global warming. None. You get shitty beliefs like that from reading Cook's website. And the strength of human-caused warming cannot be calculated from first principles. Even if all warming is assumed to be human-caused, the IPCC's climate models are exaggerating climate sensitivity by approximately double. Man's impact is simply not able to be definitively shown. If it was, it would've been done long before now.
To subscribe to alarmism you must believe that a) climate is fragile, b) climate has been relatively stable and unchanging and c) today's climate (or the climate prior to the IR) is a naturally-determined optimum that we should aim to preserve. All three are at least eminently debatable if not simply false.
The difference between warmists and skeptics in a nutshell is that warmists trust models, skeptics trust observations. So you put your trust where you please, and I'll do likewise.