Ice
This essay mentions the Younger Dryas but what it doesn't mention is that the Younger Dryas was a sudden return to glacial temperatures after the earth had already warmed up at the end of the last glacial period. The magnitude of these swings in both directions are absolutely enormous and occur at much too rapid a speed to be attributable to trace greenhouse gas concentrations. Something else must have caused those swings. Either volcanic and geothermal activity or meteoric activity are the only likely culprits.https://en.m.wikipedia.org/wiki/Younger_DryasThere is evidence of Geothermal activity under the Antarctic ice sheet. Why is magma not on the table for glacial melting? See NASA article below:https://www.jpl.nasa.gov/news/news.php?feature=6996By the way the Antarctic ice sheet is currently at median levels (based on 1981-2010 baseline): https://nsidc.org/data/seaice_index/The article also mentions 1m of sea level rise before 2100. There is no evidence of sea level rise acceleration. It is averaging 3.3 mm per year since 1993. Assuming there is not a cyclical downtrend in sea level (likely sometime this century, given grand solar minimum odds or chance of a major volcanic event), that would only amount to just under a foot per century of sea level rise. Source: https://climate.nasa.gov/vital-signs/sea-level/