C14 from solar storms and nuclear testing can be taken into account. If for some reason it was not taken into account when someone was using isotope ratios to determine how much of the atmospheric carbon is from ancient sources, or if there was some other C14 source that was missed, the result would be that the calculated amount of ancient atmospheric carbon would come out lower than the correct amount.
As for having only ~100 years of measured data, around 70% of the increase in atmospheric CO2 in the last several hundred years has taken place in the last 60 years. We have much more than enough measured data to say that nearly all of that increase in the last 60 years is due to human activity.
BTW, that also matches very well the curve you get when you try to calculate human CO2 emissions over time by looking at the known sources of human CO2 emissions and estimating their growth over time by looking at the economic records. Most of the human sources are commodities and there is extensive historical data on their markets.
As for having only ~100 years of measured data, around 70% of the increase in atmospheric CO2 in the last several hundred years has taken place in the last 60 years. We have much more than enough measured data to say that nearly all of that increase in the last 60 years is due to human activity.
BTW, that also matches very well the curve you get when you try to calculate human CO2 emissions over time by looking at the known sources of human CO2 emissions and estimating their growth over time by looking at the economic records. Most of the human sources are commodities and there is extensive historical data on their markets.