If ALL of earth's carbon was released as CO2, how warm would it get?

Tough to say. There are masses of carbon sequestered away in sedimentary rocks--several orders of magnitude more than you'll find in the atmosphere+oceans+biosphere. At a certain point a runaway greenhouse effect would occur whereby the oceans evaporate and surface temperatures would climb to several hundred degrees C (similar to what may have happened on Venus). This is quite a ways off in terms of current concentration, but it would happen well before all carbon was released as CO2.

I don't know if this actual calculation has been done, but it's not really relevant.

Almost all the oxygen in the atmosphere came from CO2 (small amounts from photolysis of water).

That's why the earth didn't freeze over when the sun was young and dim.

And if all the carbon formation were to be reversed right now, we would choke as well as fry. I don't know if we'd boil the oceans, but if we did we'd be on the way to outgassing sulfuric acid haze from rocks and become like Venus.

ALL the earth's carbon!!!??? We'd be cooked like chickens in the oven. Venus - for some reason we don't know - turned inside out. It "outgassed" - apparently volcanoes went on for so long that the insides of Venus came out on the surface - and now it's atmosphere is heavy with CO2 - among other things. And the planet is so hot your could melt lead on the surface. It's a bummer!

CO2 does not directly cause the temperature to rise. CO2, and thousands of other gases, sit in the upper atmosphere and limit solar rays from leaving the planet. These rays bouncing multiple times down to the surface of the earth causes temperatures to rise.

Well we'd all be dead as there would be no Oxygen left, so it wouldn't really worry any of us.

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