Wind is caused by uneven heating of the earth's surface by the sun. Because the earth's surface is made up of different types of land and water, the earth absorbs the sun's heat at different rates. This uneven heating produces global circulation patterns. As the abundance of energy reaching the equator produces hot humid air that rises high into the atmosphere. A low pressure area forms at the surface and a region of clouds forms at altitude. Earth's tilted axis causes the seasons. Throughout the year, different parts of Earth receive the Sun's most direct rays. So, when the North Pole tilts toward the Sun, it's summer in the Northern Hemisphere and when the South Pole tilts toward the Sun, its winter in the Northern Hemisphere.