Answer
The orbit's shape is very close to a perfect circle. There is very little difference in the intensity of sunlight we receive from the sun at different points in the Earth's orbit during one year.
The Earth's closest distance from the sun occurs in January when it is winter in the northern hemisphere.
The seasonal changes in the northern hemisphere and the southern hemisphere are not synchronized.
Work Step by Step
It is true that the Earth's orbit about the sun is elliptical, but the shape is very close to a perfect circle. There is very little difference in the intensity of sunlight we receive from the sun at different points in the Earth's orbit during one year.
Also, the Earth's closest distance from the sun occurs in January when it is winter in the northern hemisphere. If seasons were caused by differences in the Earth-Sun distance, we would expect to have summer in January.
Also, if seasons were caused by differences in the Earth-Sun distance, we would expect the seasons to change in the same way at all locations on the Earth. However, the seasonal changes in the northern hemisphere and the southern hemisphere are not synchronized.
