Abstract
Saudi Arabia (SA) has witnessed human activity in all aspects of urbanization, industrial, socioeconomic, and transportation, all of which depend on fossil fuels. The record from the period 1986 to 2014 was investigated; during this period, SA was exposed to general warming appeared through the extreme events of warm nights (TN90p), warm days (TX90p), cold night (TN10p), cold days (TX10p), tropical nights (TR), and summer days (SU). The study showed warming throughout the country. In Riyadh City, TN90p and TX90 increased by (10% and 5.1%) per decade respectively, while the TN10p and TX10p decreased by (1.5% and 0.4%) per decade respectively. TR has increased significantly in Riyadh by 20 nights and as for the rest of the stations, the highest < 14 nights. The purity of the atmosphere is introduced through the concept of solar polygons (SP) as the clearness index (K-T), which represents the amount of solar irradiation at the earth's surface relative to the extraterrestrial radiation at the top of the atmosphere. Recently,K(T)is decreased in all regions except in the east region at Al-Hafuf station. As an example, Riyadh CityK(T)is decreased from 0.63, in January during 1976-1984, to 0.41 in the second period (1986-1995), which means that 0.63 of the solar irradiation at the top of the atmosphere was penetrating the atmosphere, decreasing recently to 0.41. The study is attributed to this change to the impact of the anthropogenic activities that accompanied the large development projects during the last decades.