Which condition causes an aircraft to climb more slowly?

High temperature is a significant factor that causes an aircraft to climb more slowly due to its impact on air density. As temperature increases, the air becomes less dense, which means that the same volume of air has fewer air molecules. This reduction in air density results in decreased lift generated by the wings and a reduction in engine performance.

In warmer conditions, aircraft engines may experience a reduction in power output, and the wings require a higher speed to generate the same amount of lift compared to cooler temperatures. Consequently, this leads to a slower rate of climb since the aircraft cannot ascend as efficiently. Overall, high temperatures compromise the aircraft's climb performance.

In contrast, lower humidity can improve engine performance and contribute positively to climb rates. Low density altitude, which often occurs with cooler air, enhances lift and engine efficiency, allowing better climb rates. Calm winds also generally support effective climbs by providing stable air conditions rather than introducing turbulence or downdrafts.