I've gone over that several times - it depends on what the driver of the change is. In the warming period about 125,000 years ago, when it was the earth's orbit and angle that drove the warming, the carbon dioxide was released from the ocean *because warmer water cannot hold as much carbon as colder water*.
This current change, the carbon is leading the temperature *because the carbon is coming from us humans burning fossil fuels*. We know that it is coming from burning fossil fuels in three ways:
* We humans are producing 50-100X carbon dioxide as much as volcanoes.
* Volcanoes produce carbon dioxide by melting rock which is not burning any oxygen - the rise of carbon dioxide matches the fall of oxygen.
* The carbon dioxide increase in the atmosphere is carbon 12 which is from old plants. Volcanoes produce more carbon 13 than we see in the atmosphere, and carbon 14 only comes from plants that grew recently.
Geddit now?