Q1. Why has CO2 gone up?
The stock answer is that man is responsible through the burning of fossil fuels.
This would only make sense if the CO2 in the air was totally independent of the land, the oceans, the plants, the plankton, the biosphere. You could just increase it unilaterally and it would stay. That is in fact the core assumption of the whole man made global warming story, the 50% increase is due to man alone. It sounds possible if the air is totally disconnected from the environment except over a very long time.
Q2. Then you can ask, where has the doubling of C14O2 gone after the bombs in the 1960s?
The stock answer is in rapid gaseous exchange into the biosphere, the water, the plants, soil.
and there you have it, the massive contradiction. These things cannot both be true.
A system which exchanges CO2 is in equilibrium and in this state, you can only temporarily increase the concentration on one side but it quickly goes back to the centre. Yes, the total amount goes up but the proportion from one side to the other does not change. In this case, the ocean side of the equilibrium is 50x bigger, so neither side appears to change. (That is 98% of the extra aerial CO2 vanishes into the ocean where it adds 0.5% to what is there already.)
Each year we add 35 billion tons to a system with 100,000 billion tons. No wonder we make no difference. The CO2 level before the industrial revolution and the rapid growth of the human population was set by the planet in equilibrium, not by man. Real forces of equilibrium keep it at the one level unless there is a major change in temperature, volume, radiation or even volcanoes or crashing asteroids.
The graph of C14 after the bomb shows precisely the sort of behaviour you expect from a system in equilibrium which is disturbed. The rate at which it goes back to the equilibrium position demonstrates the rate of exchange. The rapid disappearance of the C14 rich CO2 shows dramatically that one huge reservoir of CO2 dominates all others in a single decay curve and the only candidate big enough to wipe out all the C14, the oceans.
Even worse, for a constant CO2 level to work, you would have to replace every C14O2 in the air with C12O2 and still maintain the concentration of CO2. Now why should the planet precisely put back what man added, exactly replacing new for old? Why shouldn't the CO2 concentration find its own old level?
So we have a proven, simple and clear model for CO2. Equilibrium between the air and the deep oceans which cover most of the planet. This obeys the chemistry equilibrium laws we know and understand. For this not to happen would break the fundamental law of gas exchange which govern everything from air for fish in the ocean or even our own breathing where we eliminate CO2 and take in new O2 from the blood.
Q3. If not through man, why has CO2 has gone up 50%?
As most of the CO2 is in the oceans, a quick check of vapour pressure or solubility shows that it would only take an average 1C increase in the ocean temperature to increase CO2 by 70%.
Q4. Can you prove the extra 50% of CO2 in the air is not from fossil fuel?
Yes. Fossil fuel has no C14. The C14 level in aerial CO2 should have started to drop in the 1880s and now be around 2/3 of the long term average. Firstly it did not drop at all before the bombs and after the bombs is clearly, quickly and simply returning to the same point as before the bombs. This constant level of C14 is exactly what you would expect. Man's additions with the C14 rich CO2 after the bombs or with the burning of C14 free fossil fuels simply vanish into the oceans. The old equilbrium just returns. We have had no impact on it at all even though we created a lot of C14 in the 1960s.
Q5. Do you have any other confirmation?
Yes. Firstly, according to climate scientist Dr. Murry Salby, the presumption that CO2 and CO2 alone is the predictor of global temperature is not at all true. In the popular computer models, it is an absolute assumption and the predictions of temperature exactly match CO2. There is no connection. This fundamental idea behind every computer climate model is utterly broken.
At the same time he has also found that the graph of temperature over time is able to exactly predict CO2 growth precisely if you take the area under the graph. This discovery likely exactly matches nett heat input in the ocean, which in turn indicates steady heating of the oceans which in turn would push up CO2 levels in precisely the way they have gone up. In hindsight, this is exactly what you would have expected.
Overall conclusion. To discuss CO2 levels in the air without discussing equilibrium is nonsense but equilibrium is not an obvious concept to a non scientist. It has to be explained. Once this essential concept is understood, it completely explains everything we have seen and we can even precisely predict CO2 from global temperature alone, something alarmists cannot do. Unfortunately for the alarmists, only the sun is to blame for the warming and man needs a warmer, richer, wetter, higher CO2 planet. The greatest growth in the history of man is associated with such warmer periods including the Roman period, the Renaissance and the 20th century. The periods in between were terrible dark ages where even the Thames froze over and ice covered most of Europe. We should be very glad the glaciers are gone.
Postscript: What were CO2 concentrations over time? Consider the original data from the Law ice dome in Antarctica.
How cold were the 'ice ages'?
Utah geological survey
Beware these are GLOBAL temperatures including the tropics.
Now this is interesting. At its coldest, the average planet GLOBAL temperature was 50F (10C) and at its hottest 74F (23C). So it has been much hotter, but all these temperatures are survivable, except that there would be no ice and jungle in antarctica. All the world's big coastal cities would be gone as people moved to higher ground. Still few of the world's big cities are very old anyway, so we can build them again, in time or surround them with walls as the Egyptians did every year for the 35 metre Nile flood.
The graph shows however that the world could get a lot warmer! I doubt there was much industrialization 100 million years ago but there was no ice.
From the same source, a shorter time scale and using local temperatures, not GLOBAL temperatures.