[gizmo686]

Carbon is generally not removed from the environment by photosynthesis.

In photosynthesis, CO2 is converted into sugar [0], storing the solar energy in the chemical bonds of the sugar molecule. Later, the energy is released through the reverse reaction where the sugar is converted back into CO2 [1].

Carbon is also used in biology for things other than sugar production, but in general the carbon that gets consumed by an organism eventually gets released when that organism (and the organism that ate it, and so on up the food chain) decays. This is refered to as the carbon cycle.

Under some circumstances, the carbon cycle is broken, and dead organisms end up sequestering their carbon in a place that does not allow it to return to the general environment (eg. fossil fuels).

TL;RD when we burn fossil fuels we are adding carbon to the environment. When plants consume carbon, they are moving it from the atmosphere to another part of the environment, and it almost always ends up back in the atmosphere.

[0] The full reaction is CO2 + Water -> Sugar + Oxygen, or 6(CO2) + 6(H2O) -> C6H12O6 + 6(O2)

[hackuser]

Yes, good point. I knew that but somehow it escaped me when I wrote the post. My point was, the global ecosystem can handle the release of some carbon by human activity without a problem; we don't need to go to zero.

However, the sooner and farther we reduce carbon output, the faster we reduce excess carbon in the atmosphere. There's nothing magic about zero; negative output would help too.