| Global climate patterns are controlled by the input of energy from the sun. Equatorial regions receive 2.5 times as much energy as the poles, but the atmosphere and oceans redistribute this energy poleward. Due to the tilt of the Earth's axis of rotation, the amount of energy received by the northern and southern hemispheres varies throughout the year, resulting in cold winter and warm summer seasons. The tropics - 23.45° North and South - mark the latitudes at which the sun is directly overhead on midsummer's day. They also delimit one of the three main climate zones - the warm tropical zone. The cold polar zone is the other extreme, with the temperate zone in between. |