This is some introductory discussion of the carbon cycle and its relationship to the Mauna Loa carbon dioxide data
This diagram shows the regular increase in CO2 concentration in the atmosphere since 1958 when the measurements began at the Mauna Loa Observatory in Hawaii. The annual oscillations are due to seasonal changes including the warming and cooling of the oceans and the annual cycle of photosynthesis of vegetation and its decay, particularly in the northern hemisphere.
The carbon cycle shown above connects four main regions of carbon storage - atmosphere, the biosphere, the oceans and the sediments. The latter do not show the vast amount of carbon stored as carbonate rocks and as kerogen - the material of fossil fuels. The amounts given are in units of gigatonnes of carbon [Gt C, one gigatonne = one thousand million tonnes = one Petagram - 1015 grams] and the arrows representing the flows or fluxes indicate the rates of exchange between the various regions in terms of Gt C per year.
The two important flows are those taking part in photosynthesis & decay and the flows to and from the oceans. Respectively these are ~120 Gt C per year and ~90 Gt G per year, a total of some 210 Gt C per year (other versions of the carbon cycle have the total influx/outflux at only 150 Gt C). This is a large total flow in comparison with the current ~7 Gt C per year injection into the atmosphere from the burning of fossil fuels, wood burning and cement manufacture.
It is very important to attempt to separate the changes in atmospheric CO2 due to the annual anthropogenic injections and the seasonal cyclic changes.