Joining me in the studio today is Professor Ulrich Cubasch. He's a meteorologist and climate researcher from [the Free University] Berlin.
DW: Now are these city planners from Hamburg actually preparing for something that isn't really happening? Because, as we've heard, global temperatures have not been rising for the last 15 years.
"Well, they are talking about sea level rises, and the sea level rises are continuing. So the heat which comes from the greenhouse effect goes into the oceans and the atmosphere. But currently it's more heat going into the ocean and it's not warming up so much, so the total air temperature isn't rising so much either. But still, the sea level is still rising."
And do you know why now all the sun's energy is ending up in the oceans and not in the atmosphere?
"We don't really know yet. We say it's a long periodic oscillation, so it's going up and down. In the years before we had a lot of El Niños, so it was very warm. Currently we had sort of anti-El Niño -- La Niña we call it -- so it's rather cool."
So we can't really hope for another plateau of the temperature, so we'd have stable temperatures on Earth for another 15 or 20 years?
"Well, we don't know how long it will last. But we expect it to bounce back and then it might rise even higher."
Now, in the past, we've always heard about greenhouse gases in the atmosphere. Now you're always talking about the role of the oceans. Did you actually look for the wrong factors in the past?
"Not really. It's more that the ocean was a 'white spot' [Ed. uncharted territory] in our science. And it's only in the last 30 years that the ocean was equipped with a lot of technical equipment to measure it. It was really a white spot. And currently we get a lot of data which are now evaluated."
It sounds as if there are quite a few surprises coming up in climate research. Is it possible that one day you'll find out that humankind is not to blame for global warming?
"I don't expect it. There are the physical laws in the background and things are following the physical laws. But we had a lot of unknowns and we are following up: What are the unknowns and making them knowns, hopefully."
Now you're one of the lead authors of the United Nations IPCC (Intergovernmental Panel on Climate Change) report. Are there any surprises we have to expect?
"Well, currently I don't see any big surprises. Everything is sort of continuing. But we have more data, so it's probably stronger statements which we can make."
It's already leaked through, obviously, that the sea level rise is increasing. What about those data?
"Well, the sea level rise has been underestimated -- particularly in the previous report -- because it didn't consider that Greenland isn't just melting from the top, but also from the bottom layers where it sort of sits on the rock. So this effect certainly increases the sea level rise."
So does that mean we have to invest more into adaption, instead of mitigation, of greenhouse gases?
"Well, we certainly have to invest in adaption. But these sort of figures we have -- and you could see it in Hamburg as well -- are still in the ballpark of what was predicted in previous years."
Thanks a lot for the talk, Ulrich Cubasch.