What is the most important source of carbon entering the atmosphere? What other sources?

Answer 1

This is more of a global warming question. The most important source of net CO2 increase in the Earth's atmosphere is the burning of fossil fuels.

Answer 2

Uhem ... Excuse me, I hate bring up "an inconvenient truth", but the ocean, followed by volcanos and respiration are still the main sources of CO2 entering the atmosphere, just as they have been for the last billion years. Burning fossils fuels is a dangerous perturbation because results in a significant *net* flow, after accounting for the removal rate.

Answer 3

Burning biofuels; incomplete combustion yields CO and CO2 because biomass (stuff from living things) is largely carbon. This is why we say life on Earth is "carbon based."

Biofuels include: coal, petroleum products, wood, leaves, peat, animals, animal wastes, and a host of others I can't recall at the moment. The point is, burning any biofuel will pump carbon into the atmosphere without filtering, complete oxidation, and other means for removing or preventing the carbon by products of burning biomass.