Increase in P50 results in change in oxygenation curve, which is due to decrease in
Hb-O2 dissociation curve shift to left indicates more affinity of Hb to O2 and thus less delivery of O2 to tissues. 
Hb-O2 dissociation curve shift to right indicates less affinity of Hb to O2, and thus more delivery of O2 to tissues. 
When P50 increases, the affinity of Hb to O2 decreases, or there is a shift of the curve to the right. 
Among the given options, the only decrease in pH causes a right shift of the curve. All others when decreased cause shifts to left.
pH
Oxygen
Temperature
CO2