Past sea level has varied by somewhat more than a hundred metres. This is primarily due to the growth and decay of ice sheets (mostly in the northern hemisphere) with water evaporated from the sea. The Mediterranean Basin's gradual growth as the Neotethys basin, begun in the Jurassic, did not suddenly affect ocean levels. While the Mediterranean was forming during the past 100 million years, the average ocean level was generally 200 metres above current levels. However, the largest known example of marine flooding was when the Atlantic breached the Strait of Gibraltar at the end of the Messinian Salinity Crisis about 5.2
Sea level rise if several degrees of warming are sustained for millennia. For example, sustained global warming of more than 2 C° relative to pre-industrial levels could lead to an eventual sea level rise of . Societies can respond to sea level rise in three different ways: retreat, accommodate and protect. Sometimes these adaptation strategies go hand in hand, but at other times choices have to be made between different strategies. Ecosystems that adapt to rising sea levels by moving inland might not always be able to do so, due to natural or man made barriers. Understanding past sea level is important for