What single feature is primarily responsible for the variation of climate throughout different times of the year?

The answer is angle of incoming sunlight

The Sun is the basic source of energy for the Earth which affect the growth of all living things and the Sun also affect the all the biochemical processes. We know that the amount of radiation from the Sun changes day by day due to the distance of the Earth from the Sun. The rate of Solar energy affects the Earth in two ways.

The rate of solar heating which directly affects the processes like the evaporation and condensation and indirectly it affects the cloud forming processes of the Earth. The rate at which the solar energy reaches the Earth is called as the Total Solar Irradiance or TSI. This affects the climate of the Earth in many ways.

The change in rate of cloud formation increases of decreases with the distance of the Sun from Earth and hence a warm, moderate or cold climate is formed

It also affects the formation of winds due to the low or high pressure in the water bodies and hence affect the climate in the coastal areas.

The tropical areas have hot and humid climate due to the equator which has maximum exposure to the Sun’s heat.

Hence, the Sun is one primary feature that affects the climate in the Earth.