What is most likely to cause a rise in the average temperature of earth's atmosphere in future?

Thanks for your question! 

According to NASA (National Aeronautics and Space Administration) the planet's temperature depends on the atmospheric level of carbon dioxide. CO2 is the major Greenhouse gas besides that Water vapor and clouds are the major contributors to Earth's greenhouse (NASA, 2010).

 Rapid industrialization will produced more greenhouse gases near future. On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2). This happens because the coal or oil burning process combines carbon with oxygen in the air to make CO2. To a lesser extent, the clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.  Greenhouse gases and clouds play in absorbing outgoing infrared radiation. Non-condensing greenhouse gases  such as carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons  as providing the core support for the terrestrial greenhouse effect.

References

United States Global Change Research Program, "Global Climate Change Impacts in the United States," Cambridge University Press, 2009

Mike Lockwood, “Solar Change and Climate: an update in the light of the current exceptional solar minimum,”Proceedings of the Royal Society A, 2 December 2009, doi 10.1098/rspa.2009.0519;

Judith Lean, “Cycles and trends in solar irradiance and climate,” Wiley Interdisciplinary Reviews: Climate Change, vol. 1, January/February 2010, 111-122.