Binding of oxygen with hemoglobin tends to displace carbon dioxide from blood. This is called the Haldane effect. Combination of O2 with hemoglobin causes it to become a stronger acid which, in turn, displaces the CO2 from blood. It plays a far greater role in promoting CO2 transport.
In functioning tissues, liberation of CO2 causes rise in H+ ions. Reaction between CO2 and H2O results in the formation of H2CO3 (Carbonic acid). As a result, more O2 is released into the tissues from blood.