Question

how is CO2 is added to atmosphere in excess​

Answer 1

Carbon dioxide is added to the atmosphere by human activities. When hydrocarbon fuels (i.e. wood, coal, natural gas, gasoline, and oil) are burned, carbon dioxide is released. During combustion or burning, carbon from fossil fuels combine with oxygen in the air to form carbon dioxide and water vapor.

Answer 2

Although a certain amount of carbon dioxide (CO2) occurs naturally in the Earth's atmosphere, there are several human activities that increase levels of the greenhouse gas. While some scientists are beginning to focus on rising atmospheric levels of nitrogen trifluoride, methane and soot, the production of CO2 remains a topic of concern for many people -- CO2 accounts for 77 percent of man-made greenhouse gas emissions.