More on the carbon cycle.......how little we (I) know.
The CO2 level of the atmosphere is regulated by the water in the atmosphere,
i.e. CO2 is readily absorbed by water to form carbonic acid H2CO3. The carbonic has a much lower vapor pressure than CO2 and will stay in the water. The rain falls to the oceans, which are slightly alkaline. This neutralizes the carbonic acid to form carbonate and bicarbonate (shells and coral), fixing the CO2 in even lower vapor pressure ways.
A chimney stack CO2 scrubber (e.g. to remove CO2 from burning coal, Peter's comment) works by the same principles, with CO2 rising up the stack and water raining downward. If by chance the CO2 was to accumulate to form a greenhouse affect, that means warmer global air. The warmer air means more evaporation of surface water and bigger thunder clouds. The net affect is more water in the atmosphere to rain and scrub out the excess CO2, with the bigger thunderclouds reaching higher into the upper atmosphere to get at the higher height CO2.
The warmer climate and the greater amount of rain due to the higher CO2 also means that more plants are able to grow and last longer. The greater plants density will also increase their rate of CO2 absorption. With all these affects, the tide will eventually change with the CO2 levels gradually dropping. This will lead to cooling. The lower CO2 and cooling means less evaporated water and less scrubbing of the atmosphere. Relative to the plants the cooler air combined with less rain means less plant growth, less CO2 absorption and forest fires. The latter will help increase the CO2 levels for another cycle.