What is the main cause of wind?

The primary cause of wind is temperature differences across the Earth's surface. When sunlight heats various areas of the Earth, some regions absorb more heat than others, leading to variations in temperature. These temperature differences result in changes in air density; warmer air is less dense and rises, while cooler air is denser and sinks.

As warm air rises, it creates an area of lower pressure at the surface. Conversely, cooler areas with denser air create higher pressure. Wind is essentially the movement of air from areas of high pressure to areas of low pressure in an attempt to equalize these differences. This flow of air is driven by the temperature-induced pressure differences, highlighting why the first option accurately identifies the main cause of wind.

The other choices do have a role in weather phenomena, but they do not serve as the primary cause of wind. Humidity levels influence local weather and can affect air density, but they are secondary to the effects of temperature. The rotation of the Earth contributes to the Coriolis effect, which helps define wind direction but does not create wind itself. Lastly, while pressure differences in the upper atmosphere can affect larger weather patterns, the actual wind that we experience near the surface is primarily driven by temperature variations. Hence, the correct answer