TA, do you think there would be any negative effects from doubling the amount of carbon dioxide in the air in the last 50 years?
We don't even have a firm handle on how much carbon sinks take in per year. Measuring stations in much of the old USSR are poorly handled if not neglected. We haven't really invested into proper measuring tools in the "developed world" until the latter half of the past century. So there is still uncertainty if what we have recorded "in recorded history" is even accurate.
We are not quite sure the true output of exposed soils, we do know that the thawing of permafrost in Siberia releases untold amounts of Co2 and methane into the air, but only approximations of what that would be. There is even major questions in whether trees found in the temperate areas of the world have any carbon negating effect AT ALL.
There isn't even any firm ideas of WHAT doubling CO2 in the atmosphere does to our temperature.
http://en.wikipedia.org/wiki/Climate_sensitivity. It could range from 1.5 C all they way to 10C. Some have even floated the theory that CO2 can only "trap" so much and actually "caps" at a certain point.
Not to mention the fact that we have no way of predicting what increased water vapor (as the world heats up) in the atmosphere will do to the temperature. As H2O both helps and hinders the greenhouse effect.
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So yes, I do think we have an effect. But I do not think it is significant or "speeding up" the natural process of this planet.