Quote:I computed the % of the global temperature increase caused by human CO2 emissions into the atmosphere to be quite small, assuming that "5%" figure were to remain constant.
You computed nothing of any worth.
If something contributes 5% per year, what is the cumulative effect after 5 years?
If we assume that none of that 5% is removed then we only have to figure simple compound interest which would mean after 30 years the total effect from humans would not be 5% but would instead by about 330%.
However there is a problem. There are actually 2.966 x 10^12 tonnes of CO2 in the atmosphere. Based on the numbers you have given about 150 billion tons cycle every year. If I do my math right that means that 150 of 2966 billion tons cycles every year. That is about 5% of the total which means that the human introduced CO2 is only about .2% of the total CO2 in the atmosphere. So that means if we run the numbers again and assume that all the human CO2 is retained in the atmosphere we end up with about 6.18%.
But we know that all the human caused CO2 doesn't stay in every year.
So, lets assume that the natural section cycles all the human CO2. Since all the CO2 in the atmosphere doesn't cycle every year we need to know about what % does.
There are 2.966 x 10^12 tonnes of CO2 in the atmosphere. Based on the numbers you have given about 150 billion tons cycle every year. That would by roughly 5% cycling through natural sources. Assuming that all the CO2 has a random chance to cycle in a given year. Lets do a simple list with 150 billion tons cycle naturally and no increase in atmospheric CO2.
First year - .2% is introduced by humans and 5% of the total cycles
That means 5% of the .2% of human caused CO2 would become part of the natural cycle leaving .19% of the atmospheric total as human caused. First year 6 billion tons of human CO2
Second year We add another .2% of human caused CO2 to the atmosphere. We already have .19% of human caused there so it becomes .39% which again we lose 5% of that.
Second year 11.7 billion tons of human CO2.
And so on and so on.
At the end of 30 years we would have 94 billion tons of CO2 with the atmosphere staying the same that would be 3.2% of the total CO2 would be human caused with no cycling in the natural process.
But that's not quite right either. We know that the amount of CO2 in the atmosphere is increasing. For the sake of argument we will just let the CO2 increase by 1/2 of the human caused CO2 in a given year.
The first couple of years look like this
total CO2___total human CO2__ total human CO2/total CO2
2966 _________ 6 _________0.002022927
2969 _______ 11.7 _________0.003940721
2974.8______17.115 ________0.005753231
2983.4075 ___22.25925______0.007461016
and so on to the 30 year mark
3823.566517___94.24334833____0.024648021
So after 30 years with 1/2 the human CO2 being retained in the atmosphere that means we get about 2.5% of the total CO2.
But then of course we can figure the amount of the increase caused by humans based on those numbers as well. If the effect of natural cycles are constant and random as to which CO2 molecules enter it then we would see 94 billion tons out of 1124 billion increase could be directly attributed to humans. That means that 8.4% of the actual molecules in the atmospheric increase would have directly come from human activities. Of course the molecules from human activity would on some random basis also end up back in the atmosphere which would increase the figure slightly.
That leaves us with an indirect displacement of molecules by human ones within the existing cycles.You are arguing ican that somehow when the human caused CO2 molecules leave the atmosphere they no longer are part of the normal cycle. But that has some problems because it assumes that the natural cycles have some unknown and unquantified CO2 cycle that only occurs when humans introduce CO2. That is nothing more than wishful thinking on the part of those trying to propose such a thing. There is no evidence of it existing and no reason for it to only occur at the time humans are releasing CO2.
That means we somehow have to figure the molecules that have indirectly come from humans in that they were moved into a cycle that existed already. This is where we have to figure net effect. The net effect of the natural cycles is to remove about 50% of CO2 from human activity. The net effect of human activity is that the atmosphere will retain the equivalent of about 50% of what is caused by humans. We don't have to know how many specific molecules are removed by any part of the natural cycle. We only need to know the net effect. The net effect of human activity is to increase the CO2 in the atmosphere.