What is the main cause of fading observed in radio waves?

Fading in radio waves primarily occurs due to short-term variations in energy absorption as the radio signal travels through the atmosphere. This energy absorption can fluctuate based on various atmospheric conditions, leading to temporary decreases in signal strength. Factors such as precipitation, atmospheric conditions, and even the presence of obstacles can cause interruptions or changes in the signal path, which manifest as fading.

While interference from other signals does play a role in diminishing signal quality, it typically results in a different phenomenon known as signal interference rather than fading per se. Changes in temperature and humidity can affect radio wave propagation but they tend to influence longer-term transmission characteristics rather than the short-term fluctuations that are primarily responsible for fading. Therefore, the most accurate cause of fading is indeed the short-term variations in energy absorption encountered by the radio waves as they propagate through different mediums in varying conditions.