Couple of nuances here. The CO2 "cycle" is the whole of generation and retention. BOTH the Land (plants) and the Oceans are the major players in this..
I hate it when the units are in carbon and not CO2 -- but human emissions are about 5% of the YEARLY CO2 cycle that nature sources and sinks. And after reading a lot of lit on this -- I doubt that NATURE'S contributions are KNOWN within 5% of the correct numbers.
CO2 is NOT permanently resident in the atmos and has both a long and short term time constant for residency.. All that exchange is constantly in flux and the oceans (especially the colder ones) are SUPER sinks for CO2.. This is sequested DEEP in Davy Jones locker land at great depths.
Even now -- about 1/3 to a 1/2 of man's emissions are eaten yearly by natural land/ocean sinks.
The other "nuance" is -- the greenhouse POWER of CO2 to heat the surface is logarithmically limited by increasing the CONCENTRATION in the atmos.. The MORE CO2 -- the LESS the incremental increase.. For every doubling of CO2 -- you get the SAME increase in surface temperature..
SO -- since the Industrial revolution we haven't even REACHED the 1st doubling, but from basic physics and chemistry you can find the math for an atmos GHouse model. A doubling in Concentratiion using this BASIC SCIENCE -- yields about 1.1degC increase in surface temp.. We've seen about 1.6DegC since that time.. That's from a baseline of 270ppm conc CO2 to about 410 today.. Haven't REACHED the 540ppm mark YET,.
But the IMPORTANT bit of this is that the NEXT 1.1DegC of CO2 warming to reach 1080ppm WILL TAKE TWICE AS MUCH CO2 as the 1st doubling... Not gonna finish the 1st doubling til about 2050???? Will reach 1080 by 2150??? Dont know.. That's the basic Greenhouse math in every Atmospheric Physic textbook..
But where I get off the GW crazy train is with the auxillary - MORE CONTROVERSIAL -- CATASTROPHIC theories of GW.. The ones that make people shit their skivvies with monster storms and droughts, melting of antarctica/greenland, fantastic amounts of ocean rise --- ARE NOT SETTLED science.. After 30 years of closely following the science, my position is that CO2 has power to increase surface warming, but NOT SUPERPOWERS theorized as "all positive feedbacks", "accelerated warming curves" and "trigger temperatures" at which we could no longer make a difference to outcome.,
Sorry for the length.. Appreciate your objectivity and interest.. Thought you might find some things to discover here...