Well, I'm sure human activity isn't helping, but there's one unavoidable fact: the Martian polar caps are shrinking. We're not doing that.
Solar energy decreases as a square of the distance, so Mars is getting a lot LESS solar energy than earth.
So, doing the math, if our planet gets more solar energy than Mars, and what Mars is getting is enough to make its caps shrink...
Does this mean we can do whatever we want? Of course not. We will just make it worse. Would the world change in such a way to make the climate hostile to humanity even if we weren't here? Possibly.
The fallacy of the "green" movement is that the Earth and the sun are static. It has been both far warmer and far cooler than it is now with no human intervention. It can easily become either again, and any change could possibly render the planet if not uninhabitable at least inhospitable except for the previously inhospitable regions (ie Antartica becoming a great place to live if it gets real hot and the equatorial areas being nice and temperate if things chill down).
So the question is not "is mankind changing the climate", because we know we are, it's "is mankind changing the climate enough, in combination with its own tendency to change anyway, that we or our children or grandchildren will be in severe peril, and what can we do to alleviate the problem?" It's quite possible that if every "emitter" disappeared today, whether coal burner, fossil fuel burner, gas emitter, etc, the world would continue on its merry way with no real observable difference in what is to come ie it's too late for us to change anything except for the worse. Doesn't mean we shouldn't try. But if all our efforts won't help, and business as usual isn't going to make it that much worse, how much effort should we really exert?
This is what studies should be for.
This is what they have failed to provide.