@hawkeye10,
We have a pretty good (but crude in some areas) record of the earth's geological history, but no adequate model for the changes it has undergone. We can develop some plausible after-the-fact explanations for the major changes that have occurred (mass extinctions, ice ages, warm periods, etc), but, even there, new evidence emerges that alters previous throries. We aren't even close to the ability to start with the estimated conditions in one geological age and using that, deduce the changes known to have occurred after it. That means we don't have the ability to reliably calculate a future state based on current conditions. Indeed reliable predictions may not be possible, owing to the problem of sensitive dependence on iniotial conditions that plagues weather predictions.
That said, the occurrence of a, probably geologically significant, increase in the Earth's atmospheric CO2 concentration naturally gives rise to serious investigation about what may be the consequences of it. The result, of course has been a lot of unprovable speculation about what may happen based on models of unproven merit in a situation that simply doesn't (so far) permit accurate predictions.
The interest of ambitious investigators in their own efforts to make such predictions is understandable, and the potential stakes for humanity are indeed high. However we are left with the unanswerable question of whether the problem is worth fixing. With current technologies the cost of transitioning to emission free sources of energy - without using nuclear power - is enormous. Tripling the cost of energy will have profound and lasting effects on human welfare and even population. If we take the advice and demands of the global warming zealots, there is a 100% probability of suffering these consequences, while we can't really be sure of the cost of doing nothing.
Beyond that the question appears to be moot in that, given their overwhelming committment to economic development, there is little chance of getting China or India to go along with any such program. With that restriction there is little the Western world can do to make a meaningful difference in whatever might unfold - no matter what draconian measures we may take.
New technologies, nuclear Fusion and/or a solar powered version of photosynthesis that produces free hydrogen, might do the job, but both are likely several decades away. I believe the best approach is to attenpt to buy that time. Additional use of fission nuclear reactors and natural gas as a replacement for coal might do the job while containing the growth in our emissions. That, however, is strangely unacceptable to the AGW zealots.
Unfortunately, the debate today doesn't permit such rational approaches.
