Доклади на Българската академия на науките Comptes rendus de l’Acad´ emie bulgare des Sciences Tome 67, No 11, 2014 SCIENCES DE LA TERRE, L’ATMOSPHERE ET L’ESPACE Climatologie MAIN FACTORS INFLUENCING CLIMATE CHANGE: A REVIEW Todor Nikolov, Nikola Petrov * Mini Review Written upon invitation of the Editorial Board Abstract This article is an overview of topics related to the impact of main factors and especially of the Sun on climate changes on Earth which have always had significance for the life on our planet. Climate system of the Earth is very complex and is characterized by chaotic dynamics. It has been formed and is under the constant influence of several key factors: (1) variations in solar radiation, driven by dynamic processes of the Sun; (2) changes in the orbital parameters of the Earth due to its movement around the Sun; (3) changes in the intensity of galactic cosmic rays that alter the Earth’s cloudiness; (4) geo- physical and geological (tectonic) processes that generate the internal structure of the Earth, the structure and movement of lithospheric plates, formation of mountain systems, the opening and/or closing of oceans and formation of the main geomorphological features of the planet; (5) the strong impact of human activity, its growing importance since the Early Holocene. These factors can be divided into three groups: external (astronomical and orbital), internal (Earth – geophysical, geological and geographical) and anthropogenic. Climate changes are caused by the combined effect of these various factors, among which the orbital effects are of paramount importance. The role of the Sun as the primary energy source for the Earth and a driver of global climate change is particularly important. We also pointed many controversial issues about the exact physical processes that cause climate change. Some major problems are related to clari- fication of the relationship between solar variability and solar forcing, and also to the insufficient reliable statistical data disallowing more accurate physical models leading to inability to predict the long term climatic events [ 2, 4–6 ]. Key words:: climate changes, solar influence on climate, orbital forcing phenomena, human impact on climate, climate in Earth’s history 1455