Although information regarding volcanic activity on land is available, I sense that there is more climate/weather related influence from underwater volcanic activity than is being discussed.  I'm reminded of the airline passenger leaving Australia or New Zealand looking out the window and seeing a massive blob in the ocean.  Turns out is was a hugh floating island of lava.  Further investigation revealed an underwater field of volcanos, one of which was one of the largest ever encountered.

Given how vast the oceans are, I realize it would be extremely difficult to track or monitor underwater activity, but perhaps surface temps of the ocean would provide some insight.