Final answer:
The angle of the sun's rays relative to the Earth's surface is the single biggest factor affecting how warm a region of Earth will be on a clear day.
Step-by-step explanation:
The single biggest factor affecting how warm a region of Earth will be on a clear day is the angle of the sun's rays relative to the Earth's surface. The angle at which the sun's rays hit the Earth determines how concentrated the heat energy is. When the angle is higher, the rays are more direct, leading to a warmer region.
For example, in regions closer to the equator, where the angle of the sun's rays is more perpendicular, the heat is more intense. However, in regions near the poles, where the angle is more oblique, the heat is less intense, resulting in cooler temperatures.
While other factors such as the amount of water nearby and the direction of the wind can influence how warm a region feels, the angle of the sun's rays is the primary determinant of temperature on a clear day.
Learn more about Factors affecting temperature on a clear day