This work studies how to compare the climate impact of the CO₂ emitted and contrails formed by a flight. This is applied to contrail avoidance strategies that would decrease climate impact of flights by changing the trajectory of aircraft to avoid persistent contrail formation, at the risk of increasing CO₂ emissions. We find that different comparison methods lead to different quantification of the total climate impact of a flight but lead to similar decisions of whether to reroute an aircraft.