Earth__ampersandsign#39;s climate is determined by complex interactions between the Sun, oceans, atmosphere, land, and living things. The composition of the atmosphere is particularly important because certain gases (including water vapour, carbon dioxide, methane, ozone, and nitrous oxide) absorb heat radiated from the Earth__ampersandsign#39;s surface. As the atmosphere warms, it in turn radiates heat back to the surface, to create what is commonly called the __ampersandsignquot;greenhouse effect.__ampersandsignquot; Changes in the composition of the atmosphere alter the intensity of the greenhouse effect.Variations of Chennai?s average mean temperature and diurnal temperature range for a period of ten years are investigated and is compared with past hundred years data. There is an observed variability of average mean temperature and diurnal temperature range. The variation in the temperature can be influenced by various climate forcing. In this paper we have correlated the sunspot numbers and Carbon dioxide emission with DTR and have estimated which influences the DTR more. Global warming over land can be characterized by faster warming at nights. This observed recent trend should lead to considerable decrease in the diurnal temperature range (DTR). The decrease of the diurnal temperature range is approximately equal to the increase of mean temperature1.