Why does atmospheric CO2 rise

1. Why does atmospheric CO2 rise ?

Time and again, some people claim that human activities are only
a minor source of atmospheric carbon dioxide (CO2) which is swamped
by natural sources. Compared to natural sources, our contribution is
small indeed. Yet, the seemingly small human-made or `anthropogenic'
input is enough to disturb the delicate balance. "Anthropogenic CO2
is a biogeochemical perturbation of truly geologic proportions"
[Sundquist] and has caused a steep rise of atmospheric CO2.

The vexing thing is that, in the global carbon cycle, the rising level
of atmospheric CO2 and the human origin of this rise are about the only
two things that are known with high certainty. Natural CO2 fluxes
into and out of the atmosphere exceed the human contribution by more
than an order of magnitude. The sizes of the natural carbon fluxes
are only approximately known, because they are much harder to measure
than atmospheric CO2 and than the features pointing to a human origin
of the CO2 rise.

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