Three Oxygen Dissociation curves illustrating the Bohr Effect. Increased carbon dioxide in the blood causes a right-shift in the curves, such that the hemoglobin more easily unloads the oxygen it is carrying.

See: Maynard, R.L. & Waller, R. (1999) Carbon monoxide. In: Air Pollution and Health, Academic Press, New York, Chpt. 33, pgs. 749-796.