Always pleasure GREENLEAF, just google "Plate Climatology Theory", it has only come to the fore-front of research in the last decade or so, there are many articles on it. It's in it's infancy, but as it points out, data on this underwater activity with vents and huge volcanoes that truly dwarf those on land, especially the plate faults and their ever releasing not just CO2, but methane and other gases that effect the environment, has been scarce. As you point out, many through history believed their impact to be negligible, but that opinion is being researched, new data gathered and challenged. 


Our government is very much part of the polarized political debate on climate change, sadly, when opposition presents, it is dismissed often out of hand. We assumed the underwater volcanoes and vents acted a particular way as to be of no concern, they don't throw into the atmosphere thus they don't bring cooling. 


This damn "CIVIL" format limits me from explaining, it's awful! I'd say more