1. Most, but not all, of the carbon in the earth will be turned into CO2 by humans. It will be stopped short of complete transformation by an epidemic combined with social and economic collapse which will, in turn, be caused by the rising price of getting the carbon out of the ground.
2. The epidemic in question has a simple cause which is overcrowding — not overpopulation per se but the economic arithmetic which is leading to exponential urbanization around the world. Human monocultures combined with overuse of antibiotics will inevitably lead to epidemic disease, simply because bacteria and viruses have lifetimes several orders of magnitude shorter than ours and evolve that much faster.
3. No one knows what the effect on global climate of this catastrophic release of CO2 will be. The overall response of warming is fairly linear, and thus theoretically predictable. However the global climate is a non-linear system and thus inherently unpredictable even in the short term. Unpredictable literally means “un-predictable.” No computer has been designed which can make a prediction about the effect of this warming on the global climate. The results of climate models run on computers — positive feedback, leading to a surface temperature equivalent to that of Venus, a new ice age, or something in between — are nothing better than guesses. These results cannot be assigned a probability, or a margin of error.
4. High tech methods, like photovoltaic cells, integrated fast reactors, clean coal, etc, will do absolutely nothing to stop this process. The fundamental reason for this is that humans are not smart enough to design foolproof systems. Any design-intensive solution will fall victim to the law of unintended consequences. Further, human politics are only human neurosis writ large. We are a short-sighted species and, as long as there are profits to be made, long-term rational decisions will not be made. This is because profit is a proxy for evolutionary fitness and we have no choice but to maximize it. Also, the non-linearity of the global climate system assures that hard evidence of climate change will not be available to us until it is too late to turn back. Photovoltaic cells, fast reactors, geoengineering, GM crops and the rest of it are brought to us by the same minds that brought us thalidomide, DDT, Chernobyl, the Green Revolution, and biofuels — that is minds intoxicated by hubris and profoundly conditioned by greed and short-sightedness. Minds exactly like our own.