Climate and sea level have been exceptionally stable over the last several thousand years, to the benefit of humanity, who could settle in the coastal zone and develop coastal infrastructure. Over the last fifty years, whole cities have been built in the hazardous zone of storm surges and protected against flooding through major coastal engineering. Global warming may lead to a period of much larger and rapid climate change, introducing the risk of rapid sea level rise in the future. Already today, we see a large acceleration in ice loss of the Greenland and Antarctic ice sheets, and a rapid rise in sea level over the next twenty of thirty years can no longer be excluded. Like in any other insurance problem, society is facing the risk of a large loss ...
About 20,000 years ago, when the ice sheets of the last ice age slowly started to disintegrate, Global Sea Level (GSL) started to rise from a level of about 120 m below today's average sealevel (see Figure). In many locations, coastal Local Sea Level (LSL) started to change rapidly with large drops in sea level close to the melting ice masses and a rise reaching up to 150% of the global average far away from the ice loads. Between 14,000 years and 8,000 years BP, GSL rose on average by 1.9 m/century, and in some centuries, rates were much higher.
About 8,000 years ago, GSL became far more stable, with rates soon slowing down to 0.1 m/century or less. In many areas, where no large subsidence took place, humans could finally settle in the coastal zone. Rowley et al., (2007) speculate that human civilization may have been able to develop as rapidly as it did over a few millenniums only because sea level was largely stable and allowed human settlements in the coastal zone to persist over a long time span.
The last deglaciation was not exceptional. Over the last 400,000 years and more, sea level has been fluctuating at rates exceeding 1 m/century almost all the time, and often reaching as much as 2 m/century. During these times, coast lines were shifting rapidly, and settling in coastal zone was a hazardous undertaking. Our society is challenged by the biased concept of sea level basically being stable. Nothing that happened during the time of human civilization indicates that this concept might be biased. However, the intuitive understanding is not backed by the paleo record and needs to be corrected.
Rowley, R. J., Kostelnick, J. C., Braaten, D., Li, X., Meisel, J., 2007. Risk of rising sea level to population and land area. EOS Transactions, 88(9), 105, 107 (pdf).