What is the biggest source of carbon dioxide emissions?

Answer

The biggest contributor of Carbon Dioxide is natural and not man made.
With carbon dioxide, it is important to distinguish between natural and man-made sources. One of the largest sources of atmospheric carbon dioxide is through plant and animal decay as microorganisms break down the dead material, releasing carbon dioxide into the air as part of the process. Other naturally occurring sources include forest fires and volcanoes.
Burning fossil fuels is a primary source of greenhouse gases caused by man; as the chemical energy in a hydrocarbon-rich fossil fuel is converted into heat, carbon dioxide is produced as a byproduct. Forest clearing - or deforestation - and the burning of solid waste, wood, and wood products are also sources of atmospheric carbon dioxide.