Over the geological time scale, the greenhouse gases concentration, specifically the methane and carbon dioxide have been found to fluctuate naturally. Moreover, human activities like burning of fossil fuels, use of transportation which are gasoline based and clearance of forest have contributed to changes in the concentration of gases in the atmosphere.
Various industrial effluents have increased the level of carbon dioxide in the atmosphere which further combines with the air pollutants present in the atmosphere. This traps the solar energy and raises the temperature of earth’s surface. This is also referred to as global warming. So, in the absence of carbon dioxide, global warming declines and the temperature of the earth thus decreases.

Source: ICSE book