Exactly, sort of.
How much Global Warming is due to human actions?
That is one important question. The other is: how severe is the effect in the near term and in the long term?
Answer: Nobody knows.
There will never be a precise answer any more than you can ever predict when an hourglass will run out of sand with precision. And as you point out, there are many variable inputs to the problem that man does not control.
However, we do know that the answer is greater than 0%. And the more we find out the more we can constrain the limits of the effect. And there is the possibility that we are creating the conditions necessary for a disaster to occur.