Climate scientist Dirk Notz researches sea ice at the University of Hamburg, and on Thursday he speaks at the Zukunftsfestival "Could be good" in Oberhafen. The event was organized by the citizens' faction of the Hamburg SPD. In an interview, Notz explains how progressive climate change could affect Hamburg, where he sees the greatest need for action in the city - and why it is important that climate change is discussed differently than before.
ZEIT ONLINE: You talk about "Hamburg climate neutral 2050". Is not it already too late in 2050?
Dirk Notz: The title of the lecture is not mine, it was given. As a scientist, I do not want to formulate goals or demands. In my opinion, it is not the role of science to tell people how to live. That's why I find it difficult to say: From a certain date, it's too late. I can only describe different scenarios: With global climate neutrality until 2035, we could still achieve the goal of limiting global warming to 1.5 degrees. If the world were carbon neutral in 2050, it would only be enough for the two-degree target.
Professor Dirk Notz is a climate scientist and head of the research group "Sea Ice in the Earth System" at the Max Planck Institute for Meteorology in Hamburg. © Arved Fuchs Expeditions
ZEIT ONLINE: What would the world look like in one case and the other?
Notz: An example from my field of research: In a world with 1.5 degrees warming, we assume that the pack ice would cover the Arctic year-round. With two degrees warming, the Arctic Ocean should be a sea in the summer like any other, without ice floes, without seals. The polar bears would then have to survive the summer ashore. The melting of the Greenland Ice Sheet could be stopped at 1.5 degrees Celsius, but not at two degrees - not even if it was possible to bring CO2 back out of the atmosphere and cool the climate again.
ZEIT ONLINE: Is not it frustrating for you as a scientist if such scenarios are accepted?
Notz: We scientists say the same thing for 30 years and so far, almost nothing has happened. It is becoming less and less realistic to achieve goals for the 2030s or 2040s. More important than determining which goal or which date we have to create, I find the question: How can society in a democracy be made to change faster? Personally, I do not see an answer yet.
ZEIT ONLINE: How would Hamburg in 2050, if the sea ice would continue to melt as before?
Notz: At present, the greenhouse gases that emit Hamburg emit a pack ice surface every year in the Arctic, the size of the Eimsbüttel district. But I suspect that Hamburg would still look like Hamburg in 2050 under the same conditions. Climate change is more likely to impact weather extremes here: heat, drought and heavy rainfall, for example. According to our simulations, every second summer in Hamburg would be hotter than anything we've ever experienced - when the two-degree target is reached. It would also be much more difficult for agriculture. In principle, however, such regional subtleties are still very difficult to calculate.
ZEIT ONLINE: At present, the dikes are being increased throughout the city. Is this enough in the long run? Or do we need an Elbe barrage sooner or later?
Notz: The rise in sea levels is an extremely slow process that announces itself well in advance. In Hamburg, however, other factors also play a role. It's not just about how much water there is in the ocean, but how storms develop. How much water is being pumped into the Elbe? I'm not an expert for these local scenarios, our simulations are not so small-scale. In my estimation, the protective measures in the port of Hamburg will be sufficient by 2050. I do not think that the city will be flooded in 30 years.