General weather conditions can be explained from a few basic principles. One important principle is the way the earth absorbs heat from the sun. The farther one travels from the equator the colder the climate gets - this is due to the angle of solar incidence (see illustration below).
The angle of solar incidence is the angle that the sun's rays strike the Earth's surface. At the North or South Pole the sun's rays strike the Earth's surface at an oblique or small angle, the sun rays travel through more atmosphere and are spread over a large area. This results in lower temperatures at or near the North or South Poles. At the equator, the sun's rays strike the Earth's surface at a right angle, travel through less atmosphere, and the suns rays are concentrated to a small area. This results in higher temperatures at or near the equator.
The variation in the seasons is attributed to the tilt of the Earth. In the summer months in the northern hemisphere the Earth is tilted 23.5 degrees toward the sun (see illustration below).
This increases the amount of time the sun is high above the horizon. The North Pole experiences up to 24 hours of sunlight and the northern hemisphere experiences summer. At the same time, the southern hemisphere experiences winter. Conversely, when the northern hemisphere is tilted 23.5 degrees away from the sun, the northern hemisphere experiences winter and the southern hemisphere experiences summer.