Actually, there’s quite a bit of doubt. It’s an open question as to whether or not the atmospheric CO2 concentrations we observe are comprised of independent, or dependent variables. That is to say, one might believe that CO2 concentrations are comprised of independent variables that don’t interact with each other, and any new source of CO2 (or sink) will simply directly affect CO2 concentrations. On the other hand, it is not only possible, but quite likely, that atmospheric CO2 concentrations are comprised of dependent variables, where the system can dynamically react to additional sources and sinks in a stochastic manner.
The current data suggest that in fact, the system dynamically reacts. As human sources of CO2 have increased over the years, surprisingly, and unexpectedly, natural sinks of CO2 have increased to keep pace. Let that sink in for a moment.
Imagine if we started with a 100 gallon tub that was draining at 1 gallon per minute, and was being filled at 1 gallon per minute. Then we get another hose, and add another 1 gallon per minute. Most rational expectations would be that the tub would fill with water at a net of 1 gallon per minute at that point. Instead, the drain magically opened up in response to the additional hose, and we see only 1 tablespoon per minute of increase. We redouble our efforts, and pump 2 gallons per minute more. Instead of a net 3 gallons per minute gain, we only see 2 tablespoons per minute of increase. At this point, it’s obvious that the drain is dynamically modifying itself in response to additional water input.
The same thing seems to be true of CO2, and nobody predicted it.
So do you deny that there are natural climate change drivers that we don’t know about yet, or fully understand yet? Your lack of doubt on attribution seems like quite a denial of the complexity of the biosphere, and the current limits of our observation network, and of proxy data.