During the period when the Earth is furthest from the sun (aphelion), the average temperature of the entire planet is about 4°F (2.3°C) higher than when it is closest to the sun (perihelion). On average, the intensity of sunlight falling on Earth during aphelion is about 7% less than during perihelion. Despite this, the Earth ends up being warmer during the period in which it is furthest away from the sun.
Although the intensity of light from the sun is diminished when the Earth is at its closest, the tilt of the Earth and the physical attributes of the hemispheres cause a greater average temperature when the Earth is at its furthest. This is because a much larger portion of the Southern Hemisphere, compared to the Northern Hemisphere, is made up of water and water has a significantly greater heat capacity than land. Similarly, during the summer for the Southern Hemisphere, the overall average temperature of the Southern Hemisphere doesn’t increase as much as the Northern Hemisphere does during its summer, for this same reason.
Basically, there is a lot more land in the Northern Hemisphere than the Southern Hemisphere; this land heats up much faster than water and water cools down much slower than land. So even though there is less intensity of sunlight during the summer in the Northern Hemisphere, the Earth’s average temperature is higher at this time when it’s furthest from the sun.
As you might have guessed then or already known, the seasons are not caused by the distance the Earth is from the sun, but rather are caused by the fact that the Earth is tilted on its axis 23.5°. This is why when it’s summer in the Northern Hemisphere, it’s winter in the Southern Hemisphere, and vice-verse. Without this tilt, there would be no seasons and the weather from day to day across the globe would be relatively uniform. In this case, there would be a very slight variation in temperature as the Earth got closer or further away from the sun, but for the most part, everything season-wise would stay the same year round.
Bonus Science Stuff:
- All planets in our solar system travel around the sun in roughly elliptical orbits. The distance to the sun for the Earth varies by about 1.7%. We are closest to the sun in January (perihelion) at about 91.1 million miles (146.6 million km). We are furthest from the sun in July (aphelion) at around 94.8 million miles (152.6 million kilometers). The average distance from the sun to the Earth is known as 1 Astronomical Unit, (1 AU or about 93 million miles).
- Summers in the Northern Hemisphere last 2 to 3 days longer than summers in the Southern Hemisphere. The reason why is that the Earth moves more slowly at aphelion than at perihelion.
- The date of the period where the Earth is furthest away from the sun is called Summer Solstice. The date at which the Earth is closest to the sun, is called Winter Solstice. Summer Solstice happens on June 21/22. Winter Solstice happens on December 21/22.
- In between these two points, there is a point in time where the Sun will appear to rise and set along the equator, so that the length of night and day is almost exactly equal everywhere on the planet. These two points are called the vernal equinox (March 20/21) and autumnal equinox (September 22/23).
[Reposted (with editing) from Misconception Junction]