Final answer:
The shape of Earth's orbit around the Sun is elliptical and slightly wiggly, known as eccentricity, which contributes to climate change over long periods. The tilt of Earth on its axis is responsible for the changing seasons, as it causes varying sunlight intensities across the planet throughout the year.
Step-by-step explanation:
The shape of Earth’s orbit around the Sun is elliptical with slight "wiggles" due to gravitational interactions. This shape, known as eccentricity, changes over time and affects Earth’s climate by altering the distance between Earth and the Sun, thus affecting the amount of solar radiation received by the planet. Earth’s orbit completes a full cycle of change approximately every 100,000 years.
The tilt of Earth is responsible for the seasons. The axial tilt relative to the plane of its orbit around the Sun leads to varying intensities of sunlight hitting different regions of the planet during its yearly orbit. This variation causes the seasons to change as the Northern and Southern Hemispheres alternately receive more direct sunlight.