.
>> “If the chemistry shifts just a little, such as CO2 increasing 0.01% over 100 years, slight increases in plant growth will beat it back down.” <<
.
The phyto plankton in the top half inch of the ocean will deplete it long before land based plants get a crack at it.
.
Some types of phytoplankton generate a chemical that induces more cloud cover. The evolutionary purpose might be to indirectly reduce sunlight intensity to their liking. This natural thermostat dwarfs the climate effects of humans.
Climate Control by Marine Algae
http://www.csa.com/discoveryguides/dimethyl/overview.php