Bremen city center will remain dry for a long time to come. At some point, however, the water masses will eat their way with the tide. You will overcome the ramparts on the city moat, take the Domshof and finally, when the world has warmed up by four degrees, flood the forecourt of the 600-year-old town hall.
Such a scenario threatens an analysis of Climate Central. The researchers from the US organization have used new topography and population data to simulate the global rise in sea levels. If it stayed with the current emissions path, in the long term 50 large cities would lie at least two meters below sea level and lose a large part of their currently inhabited area if dams of unprecedented proportions were not to protect them by then.
Of course, Bremen would not go under overnight. It could take hundreds of years. “We don’t know when it happens, only that it happens – we shouldn’t reduce emissions to zero quickly,” says Anders Levermann from the Potsdam Institute for Climate Impact Research (PIK). In a joint study published in the specialist journal Environmental Research Letters published, Levermann and scientists from Climate Central and Princeton University first examined the ultimate consequences of sea level rise for the world. For low-lying coastal cities in particular, they worked out what would happen in the next 200 to 2000 years at two or four degrees warming (we are currently within this range).
“We now decide how much of our cultural heritage will be eaten up by the sea.”
But why should one worry about something that is so far in the future, especially since people have enough time to relocate? “Nobody has to be afraid of rising sea levels,” says Levermann. The question is rather whether Hamburg will exist for another 750 years. Or New Orleans, Tokyo or Calcutta. “We now decide how much of our cultural heritage will be eaten up by the sea.”
The deceptive thing about sea level rise is that it unfolds over centuries or millennia. Even in the event that the states do not emit any more CO₂ overnight, the world would continue to warm up due to the long retention time of carbon dioxide in the atmosphere and the oceans would rise by an average of almost two meters in the coming centuries, so the study. Around 360 million people would now live in areas that may already be doomed, including parts of the German North and Baltic Sea coasts and the mouth of the Elbe. “Geisterland” is what lead author Benjamin Strauss, the director and chief scientist of Climate Central, calls them. “Many cities will have a wet end.”
If the world were to warm up by two degrees, as the Paris Climate Agreement provides as the upper limit, there could ultimately be an average rise of almost five meters in sea level, affecting areas on which more than 700 million people live today. In the case of four degrees, there would be an increase of more than ten meters and areas on which around a billion people live today. “If one country were to threaten another that it would have to give up ten percent of its land area, then there would be war,” says Levermann. “The same thing happens with global warming, only no country really realizes that it has to surrender part of its area to the ocean.”
Dykes hardly protect against a rise of several meters
Of the ten most threatened countries, nine are in populous Asia. These include the countries that are most driving coal-fired power, such as China, India and Indonesia. If the world were to warm by two degrees, in Bangladesh and Vietnam, for example, there would be areas of land under water at high tide, on which more than half of the population now lives.
But can’t the coastal cities protect themselves? After all, the scientists’ calculations do not assume any protective measures, and countries like the Netherlands prove that even cities that are already below sea level can be preserved. “In most cases, high dykes will not be the solution,” says Levermann. At some point the oceans would be above people’s heads. These would then have to live on in the knowledge that a dike breach would lead to an immediate catastrophe. “We have the dikes to protect us from storm surges and not to keep the oceans off permanently.”
Benjamin Strauss also sees a moral problem in relying on dykes instead of climate protection and letting the sea level rise. “We’re leaving a mess for every Generation that comes after us, “he says.” What we do in the next ten years can have an impact on the next millennia. “So the question is what legacy we want to leave behind.” If our leaders fail when it comes to climate protection, then it will be the only thing that will be remembered by us, “said Strauss.