"A large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period. Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions."

This is because most of additional energy (more than 90%) from CO2 forcing is stored in ocean. Oceanic thermal inertia is enough to keep warming in 1000 years scale without any additional CO2.