Well, if you are correct, after all of the fossil fuels have been used up, then carbon dioxide will return to Cambrian levels. The only unfortunate side effect is that mammals will cease to exist. Although, you might see a few Gorn evolving in a few million years...
But anyway, that's based on the assumption that there is a lot of coal and oil left, as opposed to only 50-100 years worth. Which is what the whole peak oil thing is all about.
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