Throughout the Earth's history, sea levels have fluctuated massively, rising and falling hundreds of feet as the Earth cyclically goes through periods of warming and cooling. Sea levels now are approximately 120 meters higher than they were 20 thousand years ago. As a collective, humans had no real effect on this process up until the industrial revolution in the 1800s. Since the 1900s, human-induced warming reached approximately 1°C (0.8°C -1.2°C). In a scenario where global warming is limited to under 2°C by the sharp reduction of greenhouse emissions, sea level rise could be contained to between 30-60 centimeters. As the current trend continues, the actual rise is more likely to be between 60-100 centimeters by the end of the century. By 2100, if sea level rise is kept to conservative predictions, some 115 million people will likely still be displaced and 420 thousand square kilometers of land could be lost to the encroaching seas. Humans have had a significant effect on thermal expansion, loss of ice sheets and melting glaciers. These three factors are the main contribution to rising sea levels.
Since scientific records began in 1880, global sea levels have risen by over 20 centimeters. In the past few decades the rate at which they have risen has increased to around 2.5 centimeters per decade. Approximately 7.6 of the 20 plus centimeters of global sea level change were seen between 1993 and 2016, faster than any period during the last 2,800 years. The acceleration in field work, data collection, mapping projections and scientific reports continues to show even more extreme outcomes from rising sea levels. New projections released in late 2019 from Climate Central show even more ocean encroachment globally, with much of Asia seeing the worst of it.
The potential cost to 18 of Europe's at risk cities is based on the latest estimations, in a scenario where no further action is taken in terms of climate change mitigation and adaptation at a 1.5°C and 4°C global temperature rise. This includes the total value of residential real estate at risk, the square meter area of property at risk and the number of residents at risk of displacement.