Do the annual variations in Earth-Sun distance adequately account for seasonal temperature changes?
1 Answer
No, the variations in Earth-Sun distance have very little effect on seasonal temperature changes.
Explanation:
The Earth is at its closest to the Sun when it is at perihelion. This currently occurs around 4 January.
The Earth is at its further from the Sun in early July when it is at aphelion.
Curiously, the average Earth temperatures are higher in July when the Earth is furthest from the Sun. The reason for this is that the Southern Hemisphere is mainly water which retains its heat. The Northern Hemisphere, which is mainly land, gets colder in the Winter than the Southern Hemisphere does in its Winter.
The main reason for seasonal temperature changes is that the Earth's axis of rotation is inclined at about 23 degrees to the orbital plane.
Near to the March and September Equinoxes the Earth's axis of rotation is perpendicular to the Earth-Sun direction. This means that both hemispheres get the same amount of solar heat.
Near to the June and December Solstices, one hemisphere is pointing towards the Sun and the other is pointing away. This is why we have seasons.
Due to precession, perihelion is getting later each year. In about 12,000 years, perihelion will be in July. At this time the Northern Hemisphere will experience warmer Summers and colder Winters because of changes in the Earth-Sun distance. The axial tilt will still be the dominant effect.
