In a normal year volcanoes emit about 1% as much CO2 as human emissions. Even such a large eruption as Pinatubo in 1991 only added 0.2% to that. Water vapor is strictly limited by temperature and can't drive climate change. The Sun's output absolutely has an effect on climate. It's just that it hasn't changed enough to account for the global temperature changes we've seen. We've had very good measurements of the Sun's output from satellites since the 1980's Those issues have all been examined by climate scientists and factored in.
Right, volcano emissions must be insignificant compared to human emissions, since they are a mere 1% of what humans emit. Before reading any further, think hard about whether or not you accept that logic, it seems pretty solid.
Here's the trick, human's emit 3-4% as much CO2 as natural sources. If the above logic still holds, we might almost dismiss human CO2 emissions out of hand as insignificant, right?
The reality is that human CO2 emissions, despite being tiny, are special in that they fall outside the earth's natural cycles. The real question is, how much impact does that small 3-4% contribution we add make on a grand scale. To answer that we need to understand what kind of flux there is in natural CO2 emission and absorption, which is openly admitted to be poorly understood, it is the consensus, if one likes that kind of phrase. AFTER that is understood, we can begin to estimate the impact of the whatever net increase in CO2 we are causing has on temperature. That means understanding the role of water vapor, as it accounts for ~70% of the greenhouse effect while CO2 is a comparatively meager 10-25%. And, once again, the 'consensus' for those that like that phrase, is that the role of water vapor is poorly understood, so much so that different climate models aren't even agreed when to use water vapor as a positive or negative feedback...
Sorry, I'm just some ignorant, unscientific heathen trying to understand things out loud.