During the last several interglacial periods, ice core readings from Greenland and Antarctica show that any increase in CO2 levels was dependent upon natural temperature increases (caused by an increase in sunlight received by changes in Earth's orbit (Milankovitch Cycles).
This means that the CO2 level increases tagged along behind the temperature increases. The ice core data shows that the 'highest' that CO2 levels ever got was 300 parts per million.
However, during our current interglacial, we are currently at 400+ parts per million and climbing due to our artificially unsequestering carbon and creating carbon dioxide. Now, temperatures are being dragged along behind CO2 levels. This describes the greenhouse effect, which was identified by Fourier in 1834, proved by Tyndall in 1859, and fully quantified by Arrhenius in 1896.
Graphic: The relentless rise of carbon dioxide-
History of climate change science: