What causes lightning?

Lightning is caused by the buildup of electrical charges within a thunderstorm. As warm air rises and cools, it creates updrafts and downdrafts, causing collisions between ice particles that result in a separation of charges. The negative charge accumulates at the bottom of the storm cloud, while the positive charge rises to the top. When the difference between the charges becomes large enough, a discharge of electricity occurs in the form of lightning. This rapid release of energy causes the air to expand quickly, creating the sound of thunder.