While there may be many relevant factors, such as elevation, latitude, the amount of cloud cover, and the condition of the ozone layer, the main culprit may simply be too much exposure to the sun.
Walaupun ada banyak faktor yang terkait, seperti ketinggian, garis lintang suatu daerah, ketebalan selubung awan, dan kondisi lapisan ozon, biang keladinya mungkin hanya terlalu banyak terkena sinar matahari.