Why the Earth is Hottest When It’s Farthest Away from the Sun

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. So what’s going on here? During the winter
months, for the Northern Hemisphere, the overall temperature of the Southern Hemisphere, where
it is summer, doesn’t change as much as the other way around. 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. On a similar
vein then, 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. So the “tl;dr” version is: 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 completely 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 only be a very slight
variation in temperature as the Earth got closer or further away from the Sun, but for
the most part, everything weather-wise would stay the same year round.

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