The Earth slowly depletes excess atmospheric CO2 due to the geological carbon cycle of silicate weathering. This is the slow, natural counterpart of the accelerated silicate weathering discussed above. It is too slow to reverse global warming on human time scales, but it means that if anthropogenic emissions ceased Earth would reach its peak temperature in less than a thousand years (ice melting and other reactions to this change would go on for several thousands of years) and gradually decline back to the pre-industrial atmospheric CO2 and climate within about 100,000 years.

My source for this recollection is David Archer's 2009 book The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth's Climate.