What is one effect of high humidity on aircraft performance?

High humidity can significantly impact aircraft performance due to the way it affects air density. When the air is more humid, water vapor displaces some of the oxygen molecules in the air. This results in a decrease in the overall density of the air, which can have several implications for aircraft performance.

For lift, the reduced air density means that there are fewer air molecules available to generate lift over the wings. This can lead to higher takeoff speeds and longer takeoff distances, making it more challenging for the aircraft to become airborne. Reduced lift efficiency may also affect the aircraft's climb rate after takeoff.

On the engine performance side, engines rely on a certain air-fuel mixture for optimal combustion. With the presence of water vapor in the air, the engine might not receive enough oxygen for efficient combustion, leading to a decrease in power output. This can affect not just takeoff but also climb performance and overall flying capability.

Thus, the combination of decreased lift and impaired engine performance makes the chosen answer correct, highlighting the importance of considering humidity as a critical factor in flight planning and safety.