Undersea volcanic eruption has caused a Snowball Earth long ago. Recent papers (HERE, HERE) and blogs WUWT, CLIMATE-ETC, ICEAGENOW showed interest concerning the impact on ocean warming, CO2 increase, and climate change. The problem is different: It could trigger a new ice age within a short period of time. The ocean is too big to reflect pronounced on a bit heat input, but may alter oceanic currents. Major changes in the global flow system would affect the sea surface. Overall ocean temperature is about 4° Celsius. The warm sea surface with more than 10°C is a very thin layer north and south of the Equator. Cooling the upper surface layer down by a few degrees Celsius could be sufficient to trigger new ice age. Mankind may have only a few months to lament about the good time of “global warming”, as the chance to alter the trend is nil, and a Snowball Earth would end further commenting pretty soon.
Nature Geoscience (January 18, 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2632.html