(a) Even though there is far less carbon in the atmosphere than other reservoirs on earth (ie the land and the ocean), it plays a very special role in the carbon cycle. What is that role?

(b) Why are there annual oscillations in atmospheric carbon levels?

(d) Why are the fossil fuels already burned to date, as well as those being presently burned, predicted to impact climate for hundreds to thousands of years into the future?

The ocean is considered to be the carbon sinks of the world and thus all the carbon there exists is absorbed by these in the formed of dissolved salts and content and this plays a crucial role in the cyclic nature of carbon.

The three annual oscillations in carbon levels are land, at and air this is due to the impact of natural fluxes. The main components being the atmosphere, biosphere and interior parts of the earth. What is known as deep carbon cycling.

These re necessary as the amount of carbon which is stored in the earth gets consumed and again produced and being a gaseous medium it's not stable in nature.

The fossil fuels that have already been burned are totally exhausted as the form of crude oil and coal. They have been burning on for centuries and have been used in lots of production processes like that manufacturing, To date, the fossil fuel has been depleted and the predicted impact is catastrophic depletion of ozone and rise of another global cooling taking place.