We don't know what other explanations there might be. Trotting out a limited number of counter-explanations like solar activity or volcanoes, and showing they don't explain the phenomenon, and therefore your pet explanation is true because it matches the data more closely, is logically specious.
We don't know the dynamics of the system. All we know is that for the data we have so far, the models work pretty well. We have no idea whether, in 200 years, these trends would lead to a 20 degree average temperature increase, a 0 degree increase or a 20 degree decrease by activating some unanticipated alternate environmental dynamic that plunges us into an ice age.
CO2 emissions as the cause of the recent temperature trend is plausible, and the results could be catastrophic, so I'm all for reducing emissions and taking every other practical measure we can to avoid the risk[1]. That's not the same as, "Anthropogenic global warming is settled science, deniers are morons, and if we don't do something now Earth in 100 years will be hell."
[1] I think the problem is, we can't agree as a society, or globally, how much we should do to mitigate it. We could spend lots of money directly, on solar power, nuclear power, electric car subsidies, etc. We could impose tremendous costs on CO2 emitting industries through regulation. But we can only speculate, based on a simplified economic model and assuming long-term accuracy of some environmental model, what the ultimate cost/benefit would be.
The science is settled, in the sense that the vast majority of people working in the field think this is probably what's happening. I think people who object to "settled" want it to mean "absolute certainty" but that's just a quibble over wording.
Deniers are morons. That's not the same as saying that there's no room for debate. There's always room for debate. But it's also a fact that the loud public face of the deniers is a bunch of politically motivated faith-based science illiterates peddling terrible rationalizations. Now, the fact that one side is full of idiots doesn't make the other side correct. But neither does the lack of complete definitive proof for one side mean that the other side isn't full of idiots.
And I've never seen anyone say that the Earth will be hell in 100 years. I have seen a lot of deniers say that this is said, in order to discredit climate change. What's actually said is that there will be a lot of disruption and chaos from changes, but of course there will always be lots of nice places to live, climate-wise. They just may not be where they are today.
