Was this AGW?
http://themindunleashed.org/2014/01/huge-underwater-pyramid-discovered-near-portugal-navy-investigating.html
The pyramid was found in an area of the mid-Atlantic that has been underwater for about 20,000 years. Considering this is around the time of the last ice age where glaciation was melting from its peak 2000 years prior, whatever civilization, human or not, that was around before the ice age, could be responsible for