Rotation axis of the Earth is tilted to 23.5 degrees. Axial tilt plays an important role for the life on Earth. The axial tilt produces seasons and mild weather.
To appreciate why it is so important for the survival of life on Earth, let's consider what happens if the rotation axis is not tilted
First of all, we can’t have more than one season. If we live near the equator, we will have summer only that is much hotter than the present one (see Fig. 1.4). The extremely hot summer causes serious climate problem. If an ocean temperature rises above 80 degrees, it will provides a sufficient condition for the formation of tropical hurricane. Thus, if the Earth is not tilted, we will have hurricanes all year round. On the other hand, if we live near the south or north pole, we will have winter only that is much colder than the present one. In either case, Earth will be a very harsh place to live.
Fig. 1.4 – If rotation axis of the Earth is not tilted, we will have only one season.
Now, what will happen if the rotation axis of the Earth is completely tilted to 90 degrees?
In such a case, we will have strange seasonal patterns. If we live in equator, we will have two very cold winters at positions A & C and two very hot summers at positions B & D (Fig. 1.5). If we live in pole regions, we will have day only (no night) for 6 months and night only for next 6 months. We going to have seasons, but summer is extremely hot and winter is extremely cold.
Fig. 1.5 – If rotation axis of the Earth is tilted to 90 degrees, people living in equator will have two very cold winters and two very hot summers. In pole regions, we will have very cold winter and very hot summer.
In solar system, Mercury and Jupiter are not tilted (0 and 3 degrees respectively) and Uranus is almost completely tilted (98 degrees). Even if we are located within the Habitable Zone, Earth will not be a nice place to live if the rotation axis is either not tilted at all or completely tilted.