Season 3

Episodes 12 and 13 – Ocean Warming, Ocean Currents, Sea Level Rise – ft. Prof. Dr. Jochem Marotzke

Episode 11 Episodes list Episode 14

In the first hald of this episode, Bea talks to Prof. Dr. Jochem Marotzke, a managing director at the Max Planck Institute for Meteorology, about the role of the ocean in climate and climate change. Jochem does fundamental research into human-caused climate change and researches the role that the ocean plays in climate and how it interacts with the atmosphere. Here, he explains how the ocean slows down the climate change by acting as a carbon sink and what consequences this has for the ocean.
Jochem describes the main reasons behind the global rise of sea level and talks about a handful of places where, locally, the fall in the sea level can be observed. He also talks about El Niño (a climate pattern of unusual warming of surface waters) and fluctuations in the global atmospheric temperature.
[A correction to what was said on El Nino and global temperature: The globally warmest year, 2016, followed the large El Nino of 2015/16. The second warmest year was 2020, not 2018, and there was no El Nino prior to that, which made 2020 all the more remarkable. Jochem said 2018 which should have been 2020.]
Bea and Jochem talk about climate change models and how they can be used to make statements and forecasts about the future. Jochem explains how we can discern the influence of humans on the temperature rise and how this discovery led to a Nobel Prise and the Paris Agreement.

In the second part of this episode, Bea continues her conversation with Prof. Dr. Jochem Marotzke, a managing director at the Max Planck Institute for Meteorology.
Bea and Jochem discuss ocean warming, greenhouse effect, interplay between the ocean temperature and the currents, and how we can measure the energy that the ocean takes, mitigating the effects of climate change but causing the imminent rise of the sea level. They talk about some of the ways to combat and prepare for the sea level rise, including some nature-based solutions, as well as about the ways to prevent further rise by cutting the carbon emissions down to zero.
Jochem also talks about renewable energy, alternative energy sources, as well as the nuclear power and the price we pay for it, literally and through long-lasting consequences of its mismanagement.

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Bea: Hello and welcome back to the Offspring Magazine the Podcast! It’s Bea and I will be hosting today’s podcast. Today, we will be talking to professor Jochem Marotzke, who is director for the department The Ocean in the Earth’s System at the Max Planck Institute for Meteorology in Hamburg, Germany. We talk about his research on the ocean and how it is affected by climate change. More specifically, we talk about the warming of the ocean, why sea levels are rising, should we be worried about sea level rising, and what are some solutions to slow down the rising sea levels. We also touch on both nature-based solutions on how to reduce climate change, but also what is the best way forward to reduce CO2 emissions. Professor Marotzke also talks about the use of climate models in his research and, in general, about his views on climate change. I hope you will enjoy this podcast!

B: Hello, thank you so much for joining the podcast today! Why don’t you just start by introducing yourself?

Jochem Marotzke: Yeah, hello! I’m Jochem Marotzke, I’m one of the directors here at the Max Planck Institute for Meteorology. And we do climate research here, at this institute.

B: Yeah, very hot topic these days.

JM: Very hot, yes.

B: Yeah, so what kind of research do you specifically do? Because climate change is such a large field of study.

JM: It’s a big field. We do fundamental research into how climate change functions. On our webpage, we say we investigate the changing climate of our earth. That’s what we do. So this is pretty broad. So we research not only the human cause climate change, we also do a lot of research on how climate functions in principle. Sometimes, how climate functions on other planets or how climate may have functioned 700 million years ago on earth. So we take a very, very broad view of the changing climate of our earth. But part of it is, of course, how humans change the climate.

B: Yeah, I think a lot of talk in the media right now is solely focused on the way that humans influence climate change. There’s not so much talk on, maybe, the natural variability or, actually, really interesting that you also study how on other planets climate change.

JM: That is true. And, of course, it’s understandable. Because what many people are concerned with, what affects people’s lives is, of course, how humans are changing climate now and what we can do about it. If we look at how climate works on other planets or may have worked or may have worked in the past, I would see that more as a general scientific interest. Maybe the same way how people are interested in how a supernova functions or the recent photograph of a black hole. And so it’s exciting for those interested in science but it speaks, sort of, freely to a very different desire compared to when people are concerned with how humans are changing earth’s climate right now.

B: Yeah. Yes, I definitely want to be going back to talking about also how climate change affects other plants because that sounds very interesting. But maybe let’s just start more by talking about specifically what you do. I saw on your website that you’re the director for, like, oceans and the influence on their atmosphere, right? That research?

JM: Yeah, I call it, when I started, I thought a bit about calling it the Ocean in the Earth system. And that’s really our program and has been ever since. So we look at how the ocean functions. But not so much the ocean per se but, really, how the ocean plays a role in climate, in the interaction with the atmosphere. And so some of what we do is purely how the ocean works but a lot of it is how ocean-atmosphere interacts. And also a big part is how ocean absorbs and transports carbon around. Carbon is very important for climate change: humans are changing the carbon dioxide concentration in the atmosphere. Some of that goes into the ocean. And there is a question” will that continue to be like that? Will the ocean continue to take up carbon? Where does that carbon go? And so that is also what we do. So very much from this, as we say, from the coupled perspective, the ocean is part of a larger system – that’s really the focus of what we do.

B: So then let’s start by talking about the ways in which the carbon… the ocean can take up carbon? And how it’s impacted by climate change?

M: Yeah, the ocean takes up about one quarter of what humans emit into the atmosphere. Very roughly, of things we emit into the atmosphere, the carbon dioxide, half stays in the atmosphere, half goes into the land biosphere: plants, all that, and the… sorry, we should start again and correct myself. Half remains in the atmosphere, one quarter goes into the land biosphere, and one quarter goes into the ocean. Very roughly. And the processes by which they go into the ocean, that carbon goes into the ocean – they are reasonably well understood. Part of it is just dissolved in the surface ocean and then some is transported downward by ocean currents: some is taken up by a plankton, by small plants in the ocean, and they consume the carbon and they die, and some of that debris falls down to the deeper ocean, and that way, takes carbon down. So we know, in principle, how it functions but the big unknown is: how will that change in the future?

B: Yeah.

JM: We know the areas in the ocean where that downward transfer occurs – it’s mostly in the North Atlantic and in the ring of ocean around Antarctica, called the southern ocean. And especially the southern ocean is very hard to predict how they will change in the future because the processes there are difficult to simulate in our models. And because they are difficult to simulate it’s hard to predict how they will change. And so much of our effort is geared towards building better models of the ocean that then will do a better, more reliable job of predicting how in the future the southern ocean will take up carbon and transport that carbon down.

B: So oceans are extremely important to act as carbon sinks, basically?

JM: They are very important, act as carbon sinks. The ocean really plays an important role here. And in some way, the ocean does a dual service us, humankind, the ocean does two things to slow down climate change. One is, as I said, the ocean takes up a quarter of the carbon. Let’s imagine a world without an ocean, then all that carbon would remain in the atmosphere and climate change would progress fast, it would proceed faster. So there’s one service that the ocean does to us. The ocean does another service: it takes up energy, it takes up heat – and that slows down the climate change. If the ocean did not absorb that heat and transfer it down, then also climate change will progress faster. So the ocean does two services: takes up heat, in a way it cools, it tempers the heating, and the ocean takes up the carbon. But the ocean also pays a dear price for that. For the carbon, it takes up the carbon, it gets more acidic – it’s ocean acidification. Which, for example, attacks some of the small animals that live, those that form shells, calciferous shells. And so the ocean gets more acidic. And it’s harder for some living entities to survive in the ocean. The other price the ocean pays – it expands.

B: Exactly, yeah.

JM: It takes up, it takes up the heat, does us a service. But it expands because it gets warmer, warmer water expands, and so the sea level rises. So that service of the ocean does not come for free and it will not go on forever. So the ocean helps us but there’s a price to pay and it won’t last for eternity.

B: Yeah, well, like with everything, there’s always advantages and disadvantages.

JM: There’s always a price to pay. There’s no such a thing as a “free lunch”. And we have that too – that slowing down of climate change through the ocean comes with consequences.

B: Yeah. So, as you mentioned, so sea levels are rising, I think most people also are well aware of the fact that sea levels are rising. So are we talking about sea levels rising everywhere or are there particular places in the ocean where the sea levels are rising more?

JM: It’s not homogeneous. So sea levels are not rising everywhere. And that’s another big part of also the research we do to understand why they are not rising the same way everywhere. For example, if you look in the tropical Eastern Pacific, sea levels have been falling over the past 20 to 30 years, they have not been rising. Now, this has been taken by climate change deniers as to poo-poo the result that sea levels go up, which is complete nonsense because of the global average, it’s very clear that sea level rises. And the fact that, in some parts of the ocean, sea level goes down a bit means it rises ever faster in other parts. Say, the Western tropical Pacific, there, sea level has risen at about twice the global rate. So there is a heterogeneity in how sea level rises. Part of it comes from how the wind drives ocean currents. And the winds may change – we’ve seen strengthening of the wind system in the eastern tropical pacific, what we call the trade winds, they blow more from the northeast, the classical trade winds, we probably all know them. And they have increased in strength for reasons that we don’t understand. And because they have increased in strength, they’ve pushed waters more to the western edge of the pacific. And that has led to this decrease in sea level in the eastern pacific. As I said, we don’t really know why that is but it’s well observed. And so one of the questions we then have and, of course, a question that people who live on the small islands in the pacific have is: will this pattern continue?  Will there continue to be more sea level in the Western tropical Pacific compared to the east? Will that pattern change? And it’s very hard to say, we’re really not sure there.

B: Yeah.

JM: And there’s another, maybe more, almost, probably exotic way of why sea level is not the same everywhere. And that is: if you look at Greenland, Greenland has a massive ice sheet, it’s about three kilometres thick, and the ice sheet is melting. And that melting ice that melts, the water flows into the ocean, and sea level rises. But there is one other effect that is not so obvious: that big fat massive ice sheet sitting there also exerts a gravitational pull, a horizontal gravitational pull on the water. And because that water that actually goes down, the gravitational pull, the horizontal pull towards Greenland gets less. And therefore, the net effect of, in the vicinity of Greenland, of ice that is melting, is actually that sea level drops in the very vicinity of Greenland, and the water is exported elsewhere. Elsewhere, of course, the sea level rises more than, more than average. So this is a really peculiar way of, and when one first hears it, very surprising aspect of sea level rise, of inhomogeneous sea level rise. And the third contribution that people in Scandinavia see very clearly: that locally there sea level also falls, it does not rise, it falls. And what we see there is that Scandinavia still recovers from the last ice age, in the sense that there was also a massive ice sheet sitting on Scandinavia, suppressing Scandinavia into the earth’s mantle – that ice melted and now we see what we call the post-glacial rebound. The pressure is away, is off, and now the land rises and the land rises faster than the sea level goes up so, locally, sea level falls.

B: Yeah.

JM: So we have a number… if you look at… if every person looked at where they live, it’s not at all clear to say by how much sea level rises. And maybe even whether it rises. But just to make that absolutely clear: where most people are, they are affected by sea level rise. If we look at many of the big cities in the world, almost all of them experience rise of the sea level, surrounding sea level – that is very clear. But the picture is complicated.

B: Yeah, it seems very complicated. I actually, when I was thinking about it, I was like, “I think maybe not everywhere sea level rises”, but you also assume that, on average, sea level is rising.

JM: On average, sea level rises. And, as I sometimes say, “sea level is like taxes and death – it comes for sure, there is no way of escaping it”. And we have already, through the warming we have created in the past, we have already committed for centuries, really centuries of further sea level rise that is completely unpreventable, unstoppable. There will be sea level rise for a long time to come, just from that one degree of global warming that we as humans have already caused. And sea level remembers that past warming history for a very very very long time.

B: Yeah. So we talked briefly about that, since the ocean is warming, that’s one of the contributing factors for why sea level is rising. Are there any other reasons why the sea level is rising, other than temperature?

JM: The main other contribution is that land ice melts. And so the large ice sheets on Greenland and Antarctica, but also alpine or mountain glaciers in the Alps, Alaska, Himalayas, there are lots of glaciers, and they melt almost everywhere in the world. 97% or so of all mountain glaciers reduce in volume. And that water eventually flows into the ocean. And that also leads to sea level rise. Currently, we estimate that about half of the sea level rise is due to the ocean warming and expanding. The other half is from land ice melting and that water flowing into the ocean. But we expect that in the future the contribution from the land ice melt will increase and will dominate the total sea level rise. There are small contributions from other effects, for example, where the land, the ground soils can store more water, the groundwater level may increase or decrease. That’s an effect that is important seasonally, say, when there is an El Niño, then that influences how much water is stored.

B: What’s an El Niño?

JM: Oh, I’m sorry. El Niño is a warming of the tropical eastern pacificю and sometimes around Christmas time, when it gets unusually warm thereб and then the whole weather patterns in and around the pacific changes. And, for example, then, where it’s normally dry, in Mesoamerica and in South America, southern North America, they may have torrential rainfalls. On the other side, Indonesia, when it’s normally very wet, they have unusual unusually dry climate when an El Niño event happens. And it’s called “El Niño”, the Spanish for “the child”, because it was first observed around Christmas – it was named after the christ child. And El Niño influences plant growth on land, it influences how much water is stored on land. So we see in measurements, when an El Niño happens, we can see some change in sea level because some more water is stored on land. But long term, that effect is very minor. And the two really big effects that you want to count is: the ocean warms and expands and there’s less ice on land and that water flows into the ocean.

B: One more brief question about the El Niño. So does that happen, like, every year? Does that happen on a regular basis, I don’t know, every five years? Or is it completely random?

JM: It’s irregular. It’s not completely random – it happens, sort of, every two to seven years. And you can see from that stretch, it’s quite irregular. But if we had a period for 10 years without El Niño, we would start wondering what’s happening. So there’s a certain regularity in it but not much. And it’s always, the height of it is always around December, January, February. And so it’s tied to the seasons. And what we always have if an El Niño event has happened, the year after tends to be very warm globally. You may say, “ah, but this is, he said, tropical pacific”. But the tropical pacific is large, it’s huge. The Pacific is a huge ocean and the tropics take up a lot of space. And so if the tropical Pacific is warmer than usual, that leaves an imprint also on the global average because the tropical Pacific is so large. And therefore, the year following an El Niño event, or a year that has an El Niño event in January, February tends to be warmer than usual. And you may have seen that, I think the last year… you know, I’m afraid I can’t quite get the name… I would have to look up the exact year where it was… 2016 or maybe it was 2018… 2018 was not an El Niño year and still it was very warm.

B: So I remember… yeah, that’s true, like, 2018 – 2019 was very very warm, yeah.

JM: I think the 2016 followed a large El Niño. And 2016 has been the record year, if I got my dates right off the top of my head. 

B: We can always, like, fact-check that and put it in the show notes.

JM: Yeah, but there was one of the other years… I think it was 2018 where… and this is why this was so remarkable that we said, “well, no El Niño to push the temperature up and still it was very warm”.

B: Do we know why?

JM: No. No, there are other things that influence the global temperatures on a year-to-year basis. Or, global temperature fluctuates on a year-to-year basis. Plus minus 0.2 degrees we could have. So for some way, for no apparent reason, a year could be warmer by 0.2 degrees or colder by 0.2 degrees. If an El Niño happened before, then we say, “ah yeah, we know why it may be warmer than usual”, but there are many other things that fluctuate. The other big part of the globe, if you wish, is Eurasia, Siberia. It’s a huge landmass. And it’s very strongly influenced by random variability in the atmosphere. So we’ve seen a period, the early 2000s say, we’ve seen a period of about 15 years where there was an unusual cooling trend in winter over Siberia. And it happened. Things, sometimes, things just happen and with no parent cause. And that also contributes to fluctuations in the global atmospheric temperature.

B: Yeah, I know. That’s why I often think, I mean, I guess, thinking a bit about climate models as well, sometimes I find it very hard to grasp how you guys measure what kind of global temperature rises because of humans, what is because of the natural variability, and then how you all put that into climate models to try to predict what’s going to happen or explain certain things.

JM: Well, you’re asking the right question: it is one of the most difficult questions to answer in our field and one of the most important questions to answer. How much of the fluctuation we see or how much of the change we see, maybe I should put it this way, how much of the change we see is due to natural fluctuation and how much is due to the human effect? And that’s very very hard to do. By now we have a clear answer on the warming, the global surface warming. And the latest statement we made in the report by the intergovernmental panel on climate change, which is this group of scientists asked by the united nations every six to seven years to…

B: The IPCC.

JM: The IPCC. To assess what we know about climate. And in our latest report, we published last year in August, we wrote “it is unequivocal that human influence has warmed to the atmosphere, the ocean, and the land surface”. “unequivocal” – there is no scientific doubt that we as humans are responsible for that warming. Took a long time to get to this certainty. But for temperature rise, we can say: this was humans, there is no scientific doubt. For other quantities, it’s much harder to say. For example, has strong precipitation, it has increased in places – was that the human effect? And if you look, and we also put that in, there’s only one region in the world, we’ve divided the world into 42 different regions, and for each region, my colleagues said: how certain are we, how much confidence do we have that it was really the human effect that led to this increase in strong precipitation? And of the 42, there’s one region, Scandinavia, northern Europe, where we are really confident that it was humans. There is one other region, central North America, where we are moderately sure it was, very moderate confidence that it was the human effect. And everywhere else, 40 other regions, there’s low confidence that the observed trend is due to humans. We just don’t know. It may well be, we can’t exclude it. And it may well emerge as human-driven change in the future. But currently, we are not sure. And so we have this huge range for temperature we are certain. For precipitation change, strong precipitation events, it’s very unclear yet. And that shows how difficult, as a general problem, how difficult this separation into human effect natural variability is. And this is why, the fact that it’s so difficult is, of course, also the reason why Klaus Hasselmann last year won the Nobel Prize in physics. He was the founding director of my institute here. And Klaus Hasselmann showed us, in 1979 in a breathtaking paper, how, in principle, we could discern the human fingerprint in all those fluctuations, in all that noise, how to go about it. And the difficulty of the problem is properly reflected in the fact that he received the Nobel Prize for that.

B: That was actually my next question: how can you, with global temperature rise, how can you be certain that it is also because of humans? Whereas then with the precipitation you’re not sure? What is there in those models that make you certain?

JM: Well, maybe the most important thing it is: it is in the observations.

B: Yes, that’s true.

JM: Modern models are indispensable for understanding what is going on and also for detecting the human influence. But at the bottom of everything is the observation and that temperatures have gone up. And what Hasselmann did was he said: “look, if I just took temperature measurements all over the globe, I have many very good records, hundreds of good stations that have measured temperature for a long time”. He showed and argued why it is a difficult statistical problem to find out that really things are going up and for a particular reason and not just like that. And what he then suggested is the following: let us, rather than trying to build the effect or the influence of humans from the individual station data and piece it together, let us use a model and let us use a model to say: what do we expect? What pattern do we expect? And models show us very clearly what pattern to expect. For example, at the surface, the arctic warms a lot faster than the rest of the globe. That’s what models show us we should expect from an increase in CO2 in the atmosphere. There’s another effect that models show us we should expect, another pattern, which is: the stratosphere should coo,l the region in the atmosphere above, say, 12-14 kilometers, depending where you are, the troposphere is where the weather occurs, the troposphere will warm, but the stratosphere will cool. And that’s a very robust result from models and we understand well why that happens. So there’s another pattern: CO2 increase means tropospheric warming, stratospheric cooling. So we have two elements of a pattern. And then Hasselmann said, “and now, let us assume the pattern is there, that’s our hypothesis, and let’s see whether we find that pattern in the observations”. And it’s much, much easier to look for a pattern than trying to piece something together afterwards. And he showed that what we call “statistical significance”, so does it, has the signal risen out of the noise, is much, much improved by doing it this way. And that was the way in which he and his group, people working with him, some 20 when was it 25-26 years ago, could identify the human fingerprint on the climate. And what’s interesting is… no, maybe we should say… well, I’ve been asked this question and I don’t know the answer, whether this idea to first define a pattern and then look for it, whether this has been used in other areas of science. I don’t know whether it has. In our field, this came out of nothing, his idea to do this: define the pattern first and then look for it. But you probably noticed that, when the gravitational waves were discovered 5-6 years ago, for which people got tone more confirmation of, general relativity theory, einstein, and people got the Nobel Prize for that, that detection followed the same principle: with a numerical model people first define patterns they were looking for in the data, and then they identified the pattern in the data that they got from those huge observatories. So that idea is much more general than just from climate research. But I am not, maybe my ignorance speaking, but I don’t know that this idea has been expressed in another field of research. And that’s another reason… so it’s a very, very generous strategy for detecting a signal in noisy data. And another reason why this deservedly, why did somebody won the Nobel Prize in physics. Because it’s really such a broad fundamental idea that it applies to many other areas of physics, too.

B: Yeah. Do you use this kind of idea of detecting a pattern first in when you study the ocean or rising sea levels?

JM: We don’t, at this institute, any longer, which is maybe a bit ironic. But the idea has taken off and is applied all over the world, say the person working with Klaus then, she was a post-doc here, Gabriele Hegerl, she’s now a professor at the University of Edinburg,h in Scotland, and many other people use these techniques. And in the reports by the IPCC, the six reports have come out, and every one of them had a chapter or a sub-chapter on, what’s called, detection and attribution, building on Hasselmann’s idea, now that they have other ideas have joined that, but the core of answering the questions “are humans responsible for this change?” is the method that that was invented by Klaus Hasselmann. So there has been a huge legacy in the field. And I would say if we hadn’t been so sure that it’s humans responsible for the observed climate change, for crucial parts of the observed climate change, I am sure there would never have been a Paris Agreement on curbing further climate change. Because the doubts would have lingered too strongly: is it really us, humans? Which implies we can really do something. But it’s it goes back to Hasselmann’s work, that we were so certain and we could already in 2015, or around 2010, we could say, “okay, there’s a there’s a tiny margin of error but yeah, just wait a bit, we know it’s the humans”.

B: Yeah. So another question about climate models that I always find very hard to understand is just: climate change is so complex, there are so many things that you need to factor in when you use climate models. So how do you make sure that you really factor in everything?

JM: We can’t ever be sure that everything is in there. So we got to be humble there. But we are reasonably certain that we’re not missing anything that’s really important.

B: And I guess, you could always change, like, maybe your climate models also change year by year? If you design them differently or you factor in something?

JM: Well, the model in the model remains the same. It may be worth explaining what a climate model is, how it functions.

B: Yeah, actually. That’s a good idea.

JM: Yes. What one way of characterizing, what we sometimes say: it’s a digital twin of the real earth. So we try to build the real earth but in a digital universe. And what do we mean by that? Most important thing is, we know the real climate is governed by some fundamental laws of nature: mass is conserved, energy is conserved, momentum is conserved, so newton’s laws of motion – these are fundamental laws of nature. We know, if you go to the very small, the very big, and so on, the very fast, that you have effects where these classic laws of classical physics are no longer valid, but for climate, we know that these laws are true and are valid. Newton’s laws of motion: energy is conserved, mass is conserved, water is conserved. And we express these conservations mathematically. There are equations that we know are correct. And then we solve these equations on computers. Now, and that’s when it gets tricky – these equations are very, very hard, they have a very complicated mathematical structure, they’re very hard to solve: we have turbulence in them, which makes life hard, which makes equations hard to solve. And so what we do is: we solve the equations not in, as we say, in the continuous form, that for a continuum, at every point in the world, this equation is valid – we solve the equation on, what we call, a grid or a mesh. We say, we have one grid point, maybe here and the next one is 50 kilometers away. And we assume that this grid point is representative for its surroundings. And when we do that, we can solve these equations on a large computer. We start from some initial state, say, what did the ocean do a year ago? And we start from that state. And then, we use the equation and the equations tell me how things evolve in the future. And that we do many times over. And then, when we’ve done, so that is also why I mean we create a digital twin – the observed world does not enter, not in the first instance, we really create a digital twin of the earth, if you wish, from scratch. It is created independently of what we observe. And what we then do is: we take observations and check how well are we doing? Did the, say, the warming, the global warming of the 20th century, do we reproduce that in a sensible way? Or temperature patterns we have, well, tropics are warm, poles are cold – the temperature drop from the topics to the pole, does our model recreate that from the laws of nature? So we’ve done, we as a field, we’ve done thousands of tests of these models. And that is also something that is often overlooked. If you at the publications in climate research and modeling papers, the large majority of modeling papers has to do with the evaluation of the models. 

B: Yeah, I can imagine.

JM: To see how well are we doing and, if we are not doing well, why is that? And that usually gives us a hint at what to do better. So we look at how processes occur, we have, sometimes you have very good observations of certain processes, say, in how the cloud forms and how the air rises, there are observations, and we try to look in models – how do the models do that? And we, when we find discrepancies, we try to improve the representation of clouds in models. And so this is also why… this goes on unnoticed by the public, this is technical work, really really important work, but technical work, for an outsider not very exciting. If I tell you, “well, the model is too warm east of Boston by 1.5 degree”, you would say, “well, I couldn’t care less”, rightly so. Why should anyone outside our field be excited about it? And that’s just fine. But it’s a foundation on which statements are built.

B: Exactly. 

JM: Which then do catch the interest of the public. 

B: Exactly, exactly. And I guess that’s also why I’m so interested in how good the climate models really are. Because in the end, you make statements based on the models.

JM: Yeah. And so what we do is: so the typical part of a large part of modeling is this type of evaluation for which we need observations, we need measurements. And that also makes this question of how good are the models for the purpose, or how good are the predictions, that makes it difficult. And in the fifth assessment report of the IPCC, the one that came out in 2013, I was one of the two people in charge of the chapter on model evaluation. And so I can tell firsthand what happened, what did people want to know? Essentially, largely, they wanted to know – tell us the models are good enough for what we apply them for but please spare us the gory details. I’m exaggerating a bit but we felt a bit like the big shady cousin of the family – we got to invite him but let’s not seat him at the center. Because the contents of the chapter is technical and I think for many people not very exciting, fair enough. But just absolutely necessary. And also difficult. I mean the epistemology of model evaluation is really hard. Because I can only check the models for the past but what people want to know is how good are our predictions for the 21st century? And that’s hard, that’s very hard. Because normally, if you contrast that with weather forecasting, I mean we’ve had thousands and thousands of days for which to check our weather forecast. Wait till tomorrow and you’ll see whether the forecasting was good. Not quite that simple, even weather forecasting evaluation, if I say a 50% chance of rain tomorrow and it rains – does that mean my focus forecast was good? So just checking tomorrow, it does not cut it. But still, weather forecasting has had so many instances of being checked. They know very well what they do well and what they do not do well. It’s much harder for us. If I make a forecast for 2100 – gee, I gotta wait 80 years to check that forecast. I mean that’s nonsensical.

B: Yeah. 

JM: I don’t want to wait, I can’t wait. And even, I mean, my forecast is always conditioned on human behavior in the future. So this is a fundamentally hard problem. And what we do is we try to make educated guesses of what we think is needed to make a good forecast. There’s a philosopher of science, Wendy Parker, who wrote about the adequacy for purpose, and she said, “let us look into the future. If I want to make a good forecast for 2050 for temperature, global temperature, what do I need to get right? What do I think I need to get right in order to make a good forecast? And then let me check back whether these things are fulfilled in the past.” so you’re breaking down the question into smaller pieces. I’m not just asking “is this a good model, this is more reliable” – that’s too big a question. But “is this model adequate for this particular purpose?” and although I can never find an absolutely definitive answer for such a long-term prediction, at least I cannot, not in my lifetime, I find decent and maybe useful answers. And that is how we work. That is why, eventually, we build trust in our models. Or where we know, we really got to be careful with models here. 

B: Yeah. Would you say that the field is mainly based on what the models predict in the future and you, kind of, research what’s going to happen in the future? Or you more look at the past and say, “this is what we have in the past and based on the past these are the decisions that we’re gonna make in the future”?

JM: I would have to guess, because someone would have to look at the actual body of literature, but my guess is that overall more work, more papers are published on the past. Because that’s where we have the observation. So all observational work, in that sense, is geared towards the past. The model evaluation looks at the past. And so even though there are many papers looking at the predictions for the future, I think the majority of the papers are published on things that lie in the past. Just out of necessity but also because at some level if you wanna… in some way models can never tell us what the world is, how the world is – that can only come from empirical evidence. Models help us explore our ideas and deepen our ideas, they help us find consistency between different observations. And so there are many many things that the models do and why models are necessary. But they can never tell us: that’s the way it is. And so, for that, there’s always, if you wish in terms of papers written, number of papers written, it’s probably always have to be a bias towards the past, it almost has to be.

B: I feel like that’s a natural thing as well. Because you’re certain about the past, you’re not certain about the future.

JM: Not at all. And I think that would have to be checked. I mean someone, almost like a sociologist of climate research, would have to check whether what I say is true, just from the published literature. But it’s definitely what I expect. That it builds a foundation for those who want to look into the future.

B: Yeah, I mean, I’ve completely sidetracked. I told myself, “in this podcast, I’m going to be talking about climate models at the end because I don’t know how many people are interested in climate models”, and then we just talked, I don’t know, 40 minutes on climate models at the beginning. So let’s go back to rising sea levels since we were talking about that. And I guess, something that we didn’t talk about yet is the ocean’s warming. So you mentioned that the oceans are warming because global temperature is rising. Is that the only reason why oceans are warming?

JM: Yeah, that’s really… and you asked why are we so sure that humans caused the climate change, in terms of physical explanation. I mean, I told you the more, the statistical approach that Hasselmann introduced. But at a more intuitive level, there’s another argument, which, physically, I find much easier to grasp. And that is: if we look at what is the greenhouse effect, human-caused greenhouse effect…

B: You know what, pause there and maybe let’s just take two minutes to explain the great greenhouse effect for people that don’t know that?

JM: What is the greenhouse effect is, let’s look at the natural greenhouse effect first, what happens – we have an atmosphere around the earth and sunlight hits the ground, the ground warms, the ground radiates back. But that radiation is caught by, what we call, greenhouse gases, it’s absorbed by these greenhouse gases. The most important greenhouse gases are water vapor and carbon dioxide, CO2. And that energy that the ground emits is absorbed by the atmosphere, by the greenhouse gases, but that energy has to go somewhere, it cannot just stay there. And then it’s re-emitted by the atmosphere, emitted upward and it’s emitted downwards. And the net effect means that the ground receives extra energy, the one that comes from the atmosphere. And that’s a greenhouse effect. So we have more radiation arriving at the ground and that leads to warming. There’s another way of putting it is that, at a certain temperature, not all of the radiation from the ground makes it to space, some of it is held back. And that is… I should start differently, I’m sorry for that. So what I just described, that’s a natural greenhouse effect, that is important to keep earth warm. What is it we humans are now doing? We are increasing the concentration of CO2, of carbon dioxide, in the atmosphere, so we have a stronger greenhouse effect. And that means there’s an additional amount of energy held back. And that energy has to go somewhere. And if you look at – where does it go? More than 90% of it goes into the ocean, it goes into ocean warming it. A little bit goes into atmospheric warming but just the amount of energy is tiny. And the reason is that the ocean is this big fat massive reservoir, this huge heat capacity, as we call it. And so the ocean warms. First, by a little, but to warm the ocean you need a huge amount of energy compared to all other elements in the climate system. And the thing is, now, we find that energy. So the greenhouse, the human-induced greenhouse effect means we hold energy back in the system, and we find that energy, we find it in the ocean because the ocean is warmed. Mostly in the upper one kilometer, thousand meters or so, but also below.

B: That was, actually, I was going to ask, whether you see the ocean warming more on the surface or more from below? Because that would tell you whether the oceans are warming because of CO2.

JM: Absolutely. And it’s very clear it wants from the surface. The heat penetrates from the surface down. And the longer we wait, the more clearly we see the warming also at greater depths. But it’s more the, typically, we could say, even the upper 700 meters. And we know why it’s more in the upper 700 meters. So it really comes from the surface. And what we can say now is that, if we think about the extra energy we held back on earth through the additional CO2, so we held the energy back, there’s one more step I need to explain – not all that energy goes into the ocean because some, of course, leads to warming at the surface but, if your surface is warmer, some of that energy makes it out of space. Not all but some. So we really have a three-way balance: the CO2 holds energy back, some of it goes into the ocean, some of it eventually leaves it, does leave the system, because the surface warms. And the big thing is: by now we have a reasonably good estimate of how much energy we should find in the ocean and, when we look at ocean temperature rise, we do find it. And even at a quantitative level, we find the right amount of energy that we should be finding, according to this three-way balance of CO2 holding energy back, some energy, extra energy leaving to space eventually, and some of it in the ocean.

B: Wait, sorry, I’m just curious: how do you study, like, how do you quantify how much energy the whole ocean takes up?

JM: We got to measure ocean temperature continuously in a lot of places. 

B: Because the ocean is huge.

JM: It’s huge, it’s humongous. 

B: Like, people can’t understand how big it is.

JM: And measuring the ocean, in a way, is painful because ships are slow and the ocean is huge. And what people have done is, and it was an idea born around the mid-1990s, that we should have floats, as we call them, which are small robots, which are deployed in the ocean and they sink to a depth of usually 2000 meters. They just follow the currents and every 10 days they rise to the surface, they measure temperature along the way they rise to the surface, they transmit the information, the data to a satellite, they sink again, and then they go on. 

B: That’s so cool, is that being used?

JM: Oh, it’s a fantastic thing. It’s called Argo, that system is called Argo, it’s Argo floats, around 4,000 of these in the world ocean. So they autonomously traverse the ocean, they live for five to seven years, one of them. And that has been the backbone, that’s why we now have a much much much better idea of measurement of the changing energy content of the ocean. And why we can be so certain now that, indeed, we have found the right amount of energy, right, in terms of consistent with how much energy has helped been held back by the additional CO2. So this is a different argument, this is not a statistical argument, this is basic physics – energy is conserved. Which means, does not mean the amount of energy remains the same, but the amount of energy we put in – we find it. That’s energy conservation in a broader term but. And that’s why I also like this as an argument for why we know it’s, why we’re so sure it’s humans. Because it’s really the very fundamental physics in its purest form, energy conservation. And then, as you can tell, even from my, sort of, simplified depiction, it’s a very very very different approach from what Hasselmann did. It’s more based not so much statistics based. But they are fully consistent with each other. And that is one reason why we are so sure – we try a number of things and they all point at the same direction. So many approaches have been tried to say: is it humans, is it natural fluctuation? And for temperature rise, the outcome is always the same. And it’s that consistency. I know of no, not a single line of reasoning, that has been checked and that has been considered valid, not a single line of reasoning that says, “there is another explanation for the observed warming”. Because there have been things that have been proposed but they have all been discredited because the effect is too small, it goes in the wrong direction. And so on. So there’s not a single valid line of evidence, scientifically by line of evidence, that says that warming is due to something else. And all lines of evidence that have been collected point in the same direction, that’s why we are so sure. It all fits together. Again, different from precipitation change, much harder for precipitation change, but for the temperature rise, this is a very clear thing.

B: So if the ocean warms because the temperature is warming, global temperature is warming, global temperature doesn’t always, is not steadily increasing, right, like, it fluctuates? So do we see that the ocean temperature also fluctuates, the same way that the global temperature?

JM: It fluctuates more slowly than the atmosphere. The atmosphere flickers, the ocean is slower and it fluctuates, but it also fluctuates.

B: That’s because it’s a lot, it takes a lot more energy to, like, cool down… 

JM: Exactly. It’s so inert. And everyone living near the sea knows that. Well, actually those living near the sea and those living in the center of a continent, or on the east side of a continent. The western side of the continent is influenced by the sea, by the ocean, the maritime climates, and the seasonal cycle is much smaller because the ocean is so inert. Or even if, in summer, you just go out sailing or go out on a boat, if you’re away from the coast by, it’s enough to be away by five kilometers, and you tell how cold it gets. You better take a jacket because out there, it’s a lot colder. And it’s just, it takes a lot more energy, as you say, to change ocean temperatures. But the ocean also, it also flickers, but much less and much more slowly than the atmosphere.

B: And the ocean warms the same amount everywhere? Or does it warm more in certain areas?

JM: It’s also inhomogeneous. Not the same everywhere.

B: And that’s again because of different currents, different winds?

JM: Absolutely. And it has to do with… the energy has to be transferred into the ocean by ocean currents, by vertical ocean currents, and they are more vigorous in some regions. In some regions, sometime,s we have very efficient vertical mixing and that also takes energy down. In other regions, we have currents, fairly steady currents that tend to go down and take heat with them. In other regions, say, typically come back to the tropical, to equatorial eastern pacific, there we, typically, have upwelling, as we call it, upward currents, they bring the cold water from beneath and they make it harder for the warmth to penetrate, so that does not warm as much. And so, depending on the current systems, you have a greater or lesser degree of warming in the ocean.

B: So the currents affect how much warming there is in certain places? But doesn’t ocean warming also affect or change the currents?

JM: Absolutely, yes.

B: So, again, they both work together so that makes it very complicated.

JM: That’s complicated. And what the ocean currents, what they are governed by is by two things really: one is the wind blowing at the surface and the other is by temperature or density contrasts or horizontal density contrast. And density depends on temperature: if temperature goes up, density goes down. But density also depends on the salt content: the saltier the water, the denser it is. And if you have a region with very strong temperature contrast, that’s where you typically have strong currents. If you cross the gulf stream, for example, that’s how sailors, 200 years ago, discovered the gulf stream: if you come from the south and cross, go to the northwest, and cross across the country and, say, again, towards Boston or so, you cross the gulf stream, but you, suddenly, find it, it gets much much colder at the surface. Over 50 kilometers, you may have a temperature drop of, maybe, up to 10 degrees or so – really really a lot. And those very large temperature contrasts over a small spacing horizontally, they, usually, they come from the strong currents, and we understand why that is, we understand that…

B: Wait, sorry, I have a really quick clarification I want to make: so is the depth of the ocean always the same?

JM: No.

B: Because that, surely, also influences the temperature change?

JM: Yes, but in a more, much more subtle way.

B: Oh, okay.

JM: And the currents near the surface often don’t feel the depth, the depth relief, as we say, they are shielded almost. It’s not universally true and not everywhere. But often yes, the ocean, so floor is rugged, but the surface currents don’t really, don’t always feel that.

B: Okay, good, thanks. 

JM: But, as I say, what they do feel is temperature contrasts, density contrasts. And here we’re at this point that you’re making. So the density, sorry, the current’s influence, they influence the temperature, but then the temperature also influences the currents. And that makes the ocean difficult. Because if you look at that mathematically, you see: this is a really really difficult situation, it’s what we call a non-linearity in mathematics. That things don’t just depend on temperature, velocity, or so on. But things depend on temperatures squared, that’s not linear. And whenever things are nonlinear, they easily get completely out of hand mathematically. And this is why, even at the very basic level, ocean circulation is difficult, theoretically, because of that interplay of temperature, temperature differences and how they steer the flow, so to speak, but then the flow influences the temperature differences in the temperature gradients and contrasts, and that makes it hard. This is why we struggle simulating the ocean well.

B: Yeah, exactly. And I can imagine it’s also a lot harder to simulate the ocean as opposed to land, the land is probably a bit easier? It’s just because, with land, I feel like we have a lot more information because it’s easier to study, whereas the ocean, it’s also so deep, you’re not going to go 10 kilometers down to study the ocean.

JM: It’s difficult, but it’s difficult in a different way. Land is not as turbulent, that’s true. But land is terribly heterogeneous on a very small scale. In the ocean, contrasts, they’re easily wiped out because you have currents, they just flow horizontally. On land, you can’t. And that is, that heterogeneity is why land is hard. Difficulties arise in a very different way. And there’s one other thing that makes it hard: okay, the ocean is non-linear, it’s mathematically difficult, but it’s governed by the fluid equations, by the laws of motion, newton’s laws – mass conservation, energy conservation. By contrast, there is no such a thing as an equation for a tree – it does not exist and I doubt it will ever exist. Of course, also when trees grow and decay, you have energy conservation, water conservation, carbon conservation. But that is not sufficient to describe how an ecosystem functions. Now, photosynthesis is governed by some law so there are equations that can be used, are being used to simulate the land biosphere. But you reach the limits of what you can base on laws of nature very quickly. So people who simulate land biosphere, they have to resort a lot more to plausible assumptions, rather than laws of nature that we do when we simulate the ocean. So their difficulty arises in a very very different way.

B: Yeah, so it’s just hard no matter what, it’s just always hard.

JM: It’s hard in a different way. And also, for the atmosphere, is also hard in a different way: those basic currents, how density difference influences currents, and so that interplay is easy in the atmosphere. Because the… for reason that probably can’t go into. The typical swirls you have in the atmosphere, they are much bigger than in the ocean. So a low-pressure system that brings rain, it’s a thousand kilometers wide. The corresponding piece in the ocean is maybe 50 kilometers wide. So much harder to resolve. But in the atmosphere, they have a lot of other problems: they have clouds, they have phase transition, they have radiation interacting with clouds. So the atmosphere has a much richer set of phenomena than the ocean has. But just the fluid motion of the ocean is a lot harder to simulate than it is in the ocean that, as we say, the fluid dynamics itself is much harder in the ocean than the atmosphere. But the atmosphere, again, has a lot of other things that make their lives hard. So the difficulties lie, sort of, in very different pockets. And what we sometimes find also: different difficulties attract different people is what we find. So that’s also curious.

B: Yeah, that is. So we have oceans warming and that contributes to rising sea levels, how much should we be worried about the rising sea levels?

JM: If you’re a planner, you should worry a lot. Because, as I said earlier, sea level rise as a function of warming is as certain as taxes and death are certain. And it will come. And we are committed to a certain level of sea level rise, not immediately but in the long term. And very very very roughly, we can say, over thousands of years, we’re quite sure that every degree celsius of global warming will bring one meter of sea level rise, give and take, roughly, a global sea level rise. Now, we haven’t done that, we’re not there yet, we have one degree of warming, and we’re far away from one meter of sea level rise. We just wait long enough, it’ll come, inexorably, it will come. And even within the century, that we may get, if we keep increasing emissions, we may get one meter of sea level rise. If we don’t increase emission so much, it may be less. But it will be quite a challenge to limit sea level rise to 50 centimeters, globally. So it will come. And 50 centimeters may not sound so much but the thing is, of course, if you think of coastal protection, of course, you have other effects: your storm surges, for example, like, here, in northern Germany. And the storm surges, they ride that background sea level rise. And, of course, it makes a big difference whether the storm surge gets to just below the crest of a dike or 50 cent centimeters more to spill over. And there are many parts of the world where people are not well prepared for future sea level rise. Bangladesh is the poster child, they’re taking some measures, relatively inexpensive measures, to build differently more. It houses, if necessary, might be able to float a bit and so on. But still, I mean Bangladesh is so low-lying and so poor of relief. And that sea level rise will hit Bangladesh hard, that’s very clear. Many big cities are right next to the coast. And even things like waves, I think, a wealthy powerful country like the united states, a hurricane Sandy, which okay, was tough luck in a way, that hit New York city head-on, but just the flooding of the subway and so on. And the risk just goes up with sea, more sea level rise. So another hurricane like Sandy hitting would mean, may cause greater problems if sea levels rise by a few tens of centimeters. So sea level rise is really one of the things that humankind must prepare for very very clearly. And it’s not some exotic thing that might happen if some free accidents all come together. It’s coming for certain.

B: So you say “it’s coming for certain”, are there ways that we… what are the best ways, I guess, would be a better way to phrase my question, what are the best ways in which we can prevent or slow down the rising sea level?

JM: It’s generally true, to slow global warming, we need to reduce emissions. That’s the truth. 

B: So still, find ways to reduce emissions.

JM: Reduce emissions, reduce emissions, CO2 emissions have to go to zero if you want to stabilize temperature. We have to reach zero. That has not sunk into quite a number of people. We’ve got to go to zero if you want to stabilize temperature. Stabilizing sea level is much harder still. So we…

B: Just because glaciers are melting anyway…

JM: Yeah, they melt from the past warming. The past warming, as I said earlier, the past warming commits us to quite a bit of future sea level rise. And so, for some level of sea level rise, there’s just nothing we can do. But we can prevent further sea level rise. But it’s also clear, because some of it we already committed to, we really need to think about better protections against sea level rise.

B: Yeah. I guess that was also what I was a bit alluding to. I mean, there’s always the argument that we need to reduce CO2 emissions, but I think there’s less talk on ways that we can, other ways that we can prevent the sea rise. I heard, for example, like mangroves could be used?

JM: Protecting. We would not prevent the sea level rise but we would prevent the effect of sea level rise. 

B: Exactly.

JM: And yes. And I think that is one of the areas where, what it’s now fashionably called, nature-based solutions, where they are really powerful. I’m more sceptical about nature-based solutions when it comes to mitigation, to preventing, to reducing emissions. But certainly, when it comes to adaptation, and especially against storm surges and sea level rise, nature can be a great help. And then there are examples already. So I have a colleague here from geography, she works on also the social the social aspects of protecting yourself against sea level rise. And she has examples from some small islands and also poor communities, where you say that technological solutions are by far not as good, they’re good examples. You build a wall here, that means where the wall stops, it gets all the much worse. And so built like mangroves, building them out there, slowing down the waves and so on, basically, to take the edge off what is coming. I think another example is New Orleans, which was destroyed by the hurricane Katrina in 1995, that also showed how poorly protected New Orleans was against storm surges. And I heard recently, apparently, some of the measures that were taken go in that direction. I mean, rather than just building a wall, think how you can make nature work in your support. And I think, generally, when it comes to how to deal with climate change, I think more should be done on accepting that some of it will happen and how can we prepare for it? How can we protect us from it? It’s sometimes not popular. And it’s gotten a bit better in Germany but, say, if I’d said in 20 years, gee, some climate change is going to happen anyhow, so let us prepare for it – some people who said it, they were accused of defeatism and say, “hey, you’ve already given up”, and almost, “you’ve joined forces with the enemy, you’ve given up on trying to mitigate further climate change by wanting to spend money and effort on adaptation”. 

B: Yeah. 

JM: Which is, I think it’s a silly stance. Because we have to prepare – some of it is going to happen for sure, like sea level rise. Some other things, we don’t know, they may happen but we don’t know. Heavy precipitation – it’s just so hard to predict. So there we better prepare for a certain range of outcomes. We don’t know what will happen. But we have a large spread of possible futures there and we better prepare for that spread. Again, that is preparedness. And the difficult thing there is that okay, so you prepare for a possible disaster and it doesn’t happen for 30 years, then people come and say, “hey, we’re wasting our money, see, nothing has happened what have you told us?” and we’ve seen that last year in Germany, the terrible floodings, which people were very quick to jump to conclusions – it was climate change. I kept my mouth shut, I was really glad, no one was asking me right after. Because what I should have said, and now can say, would have come at the terrible, completely wrong moment: that if you look at the fatalities, only a small amount is climate change and most of that is just complete lack of preparedness. And that is so. But that’s not something you could say the day after.

B: Oh, definitely not. 

JM: It would have been, sort of, smarter that coming in and maybe playing in the hands, in that case, playing the hands of climate change deniers. But now, with a bit of a distance, I mean they had no warning systems to speak of, the sirens have been disbanded after the end of the cold war in Germany. And if someone had said, “gee, we need to well we have a river that could go wild”, and probably the answer would have been, “are you nuts? I’ve lived here for 50 years and nothing has ever happened, what are you telling me?” well, I should have told, look the real, the last really really terrible flood was 200 years ago. And that’s what we just saw repeated, apparently. But to argue with something that happened 200 years ago and then to say, “we got to spend money on protection”, that’s a tough battle to fight. And I have no recipe for how to do that. But what we’ve seen, in both, in Nordrhein-Westfalen and in Rhineland-Palatinate, it was parallels in lack of preparedness in both states. That is breathtaking but maybe understandable. Because gee, hasn’t happened for as long as we can think back so why should we prepare for something that’s not on our minds. Well, we know the answer why maybe we should. But it’s very hard to prepare for something that is not on our minds, let me put it this way.

B: Yeah, I mean I also, I like to stay optimistic right now. I mean, as a scientist, I feel like I need to stay optimistic as well, but that science will be able to find nature-based solutions to help slow down or prevent huge disasters from happening because of the rising sea levels.

JM: My throat is getting dry. 

B: I mean, you’re definitely talking a lot more than me.

JM: It’s true but you also have a fair share. Which should be – we want to have a dialogue here, not a monologue. 

B: Yeah, I mean, it’s the expert always, it’s more interesting when you talk than when I talk. 

JM: No, no. But what do you throw in is very important because, I mean, I can tell that you prepared very carefully. 

B: It’s just, it’s a very interesting topic. And I think in the public, we also see so many different opinions on it. We see people that are very apocalyptic about climate change, that it’s, you know, doomsday, like we’re all going to die. And then we have the climate deniers that think it doesn’t exist. And then we have, like, a wide range in the middle. And so sometimes, I just, I like to think about all the different opinions and see well, where do I even stand? And it’s good to talk to an expert about it, any scientist about it.

JM: Because yeah, some of it is opinions but some of it is not. And there are a few things we do know, it’s not as if you knew… as if everything was just up in the air and completely uncertain. No, some things we are unsure about. And it’s really important, I think, to make that distinction clear enough, you know, some things are beyond doubt and some others, we just don’t know. And I think we need to keep that separate.

B: Yeah, I just quickly… because we’re talking about nature-based solutions, so we mentioned the mangrove swamps, that I guess, for the audience, if they don’t know about it, I think mangrove swamps, they act to rise the land faster than the sea levels, right?

JM: Ah, I didn’t even know that. But I take your word for it. I thought it was just breaking the flow but okay.

B: No, so that’s what I heard. Because they take up a lot of the soil and so that’s why they can actually rise the land faster.

JM: That’s really effective.

B: Exactly. And then they also, obviously, act as a carbon sink. But so I heard that that is a nice nature-based solution to think about, to prevent rising sea levels. Do you know any other nature-based solutions?

JM: No, I’m really… in terms of protecting against the seas, not really of the top of my head, in addition to the examples. But well, then I have to say, when it comes to technology, that’s not really my strong point.

B: Yeah, of course, of course. 

JM: So the thing where I’m more sceptical, like, I can say, is also something you think when it comes to the mitigation part, like, afforestation. Now, it’s clear we should not deforest, it’s clear we should not cut down the amazonian rainforest – that’s a terribly bad idea for a number of reasons. But afforestation is often overestimated in its efficacy. 

B: Yeah, with “afforestation” you mean planting trees as a carbon sink. 

JM: Really planting trees, deliberately planting trees as a carbon sink. And, because the one thing we have to think about, and that’s sometimes forgotten, just like for every ton of CO2 we met into the atmosphere, only half of it remains in the atmosphere, every ton we take out of the atmosphere and that goes into tree, only half of that becomes effective. Because in a way, the other half then comes out, relatively speaking, comes out of the ocean and the land biosphere. So we have that reverse effect too. So if we pull CO2 out of the atmosphere, in whichever way, half of it is being replenished by the ocean and the land because they then take up less than they originally did.

B: Yeah. Yeah, that makes sense. For me, I guess, the main thing that I was thinking about planting trees – I find it a bit of a, it’s a short-term solution but I don’t see it being a long-term solution. Just because, when the trees die, they release all the CO2 back.

JM: Yeah, it may buffer the effect. And there are people thinking about, if you used more wood for construction, rather than concrete, cement production is also a big CO2 emitter, so we may… it will not be the big solution but it may have an effect. And I think, as long as we understand that whatever we do we cannot escape the complete transformation of our energy system, we got to bring CO2 emissions net, the net to zero, and that requires a gigantic worldwide upheaval of the current energy supply systems. As long as we understand that, we are not getting away from that, I would say all contributors are welcome. So if you plant more trees, it may have other effects too. Maybe we log the trees and use them for construction work rather than cement, good. But we just shouldn’t fall into the trap of believing that planting trees will solve the problem. As long as we burn fossil fuels we’re not solving problem. That’s just true from the magnitude of it, we’ve got to be aware of it.

B: I agree. Yeah, we talk about reducing CO2 emissions, we do live in Germany, where a lot of investment has gone into renewable energy sources, but we do not have any nuclear energy. Do you have an opinion on that?

JM: Yeah, think the, by and large, I think the way the germans took is the right way: if you think about using nuclear power and then shutting it down, and that was haphazard there was no strategy, and the conservative government first extended the lifetime and then, after Fukushima, they very quickly said, “we want to get out quicker”. I think, had they decided to phase out nuclear power on a somewhat longer term, I would have had no problem with that. What sometimes people say, “nuclear power is the solution for the climate problem”, then I say, “nope, it’s not, it’s much much much too expensive”. There’s one country in the world that builds nuclear power plants to schedule and to a budget. And that’s South Korea. Every other country has humongous cost overruns and time overruns. So by the time we have built those nuclear power plants, it’s too late almost. Well, one could say, “it’s never too late”. But we’re talking about a 50-year period, in which we want to bring CO2 emissions to zero. And it would take this time to build a fraction of the nuclear power plants. So there’s a big distinction between keeping them running and building new ones. There’s another example: if you look at the total supply of nuclear power worldwide, in terms of gigawatts, power created, the installed power of new renewables, the currently installed powers, in two years, it’s the same power as all nuclear power plants together. 

B: Okay, wow.

JM: Now, that may not be usable the whole time, fair enough. But even if we discount that and say it’s 50%, then it will be at four years. And that’s what we’re doing right now. And that’s compared to all nuclear power plants together. So to me, the belief in building more nuclear power plants is completely misguided because it misses the opportunity of creating power from renewals. Plus, of course, storage – storage system, intelligence systems, they have to be built, they don’t exist yet. But if I look at how long it takes to build nuclear power plants, even in countries that are favorable, like Britain, even they have huge trouble with the new plants they are trying to build right now. So from a purely practical standpoint, it’s not going to work.

B: Wouldn’t you think it would be more efficient, though, to keep the ones that we already have yes running?

JM: Yes, I think I would have…

B: Just because the cost is not… because the cost mainly comes from building a nuclear power plant.

JM: They are written off. And the completely still, completely unsolved problem of what you do with the nuclear waste, the problem is huge and unsolved. But it’s getting marginally bigger. No, I think I would have… that I thought it was too quick to move out. But as I said, there was no, there was no real strategy. I mean the social democrat green government said, “we want to phase out nuclear power plant”, and then the conservative government extended the run time, and they said, “we were getting out faster”, I think it was faster than even planned before. So that was all, sort of, just reacting to the current situation.

B: I think also, maybe, reacting to the public’s opinion.

JM: It also, yes. And I think in both cases, I think I would have wished for a bit more rational policy. But still, I think, by and large, I mean it is sometimes, by circles also in Germany, “oh, you’re giving up on climate change mitigation by phasing out nuclear power” – I disagree with that. I really think the way to go for renewables, that’s the thing. And it’s a lot cheaper, we see that. We see now how the price of renewals, how dramatically cheap they are for power production compared to others. And in a way that no one would have foreseen. And so I think that direction is very clear. Now, it’s only part of the issue. Transportation is hard, buildings are hard. But I would say, it’s also, part of the argument is political. I think that if we don’t even manage for power production, for electrical power, then how are we going… if we don’t solve the relatively easy problem, how do we solve the harder one? So it’s also part of creating a momentum. Now, that is not an economic argument, that is not… this is really a political argument to say “let us build a success story”, to say “okay, look, we can do it”. Okay. A – we can do it, and b –  we’re not suffering by doing it, we’re actually doing fine by doing it. And I think we need those, sort of, success stories. Because if we don’t have them, if prevention of further climate change is being perceived as just a sacrifice, just something you don’t want to do it but you have to, then it’s not going to work. Because no one is playing a sacrificial lamb for the whole world, it’s not going to happen. We know it, there’s plenty of empirical evidence that people are not willing to do that. And so I think these kind of success stories and saying, “look, we manage a transformation of part of what we do and we’re doing well doing that”. I think that that’s the way to go.

B: Yeah, so you think that using wind, solar, I guess those would be the two main renewable energy sources that you could use here, in Germany, you think that yeah, in the upcoming years that would be the best solution to get to net zero?

JM: Yes, absolutely. 

B: And you also think that it would be possible for Germany to get to net zero just. Or would we still need to be using natural gas? Just because solar and wind don’t give you constant energy supplies.

JM: I’m sceptical about the natural gas but that may be the thing, especially the debate we’re currently having about – do we prepare for more use of natural gas and liquefy natural gas? I don’t know. And I don’t envy our economics and climate minister, who’s now being beaten by the green movement, and saying “how can you invest in liquefied natural gas?”. And I say: maybe they are right, maybe maybe not? Because, I mean, as often in climate, we have the tension between short-term and long-term interests. And if you don’t serve the short-term interests, you have a crisis, you have a short-term crisis and you’re out of office quickly. So you can’t just bank on the long-term interest, this is not going to work. So I don’t know whether they are, the current government is betting too much on gas, maybe they are. But I find that hard to judge. What I am sure of is one thing: it would be too short-sighted only to look at solutions within Germany. I do think that we have to look more broadly and more at the European level. I mean, we have the story like solar energy and photovoltaics and the question of, like, there was this company, desert tech, they tried to build it in morocco, I think. 

B: Okay, I have not heard of that.

JM: That was about, I think, it started 15 years ago and died 10 years ago. Because of the political instability in northern Africa. And, of course, you got a chance to transport that power. But now there’s more discussion in Spain. I mean, Spain has kind of, almost desert, I’m not sure what the official classification is. So a collaboration with Spain, I mean about photovoltaics, in Spain, maybe built with german money, German investment would, could make eminent sense. Again, transmission losses and so you have to think about it. And I don’t know what they are and what can be done. But I am quite sure that, if you think more broadly about European countries collaborating on that, but this may well be the thing. I’ve heard people say, “oh, Germany can never be climate neutral, even with power, they cannot do that”, and that sometimes said, “what’s all this nonsense?” well, that’s the wrong conclusion. I mean it may well be true that german cannot be completely self-sufficient. But the conclusion cannot be that we keep importing oil from Russia.

B: Well, exactly. 

JM: But the conclusion then has to be: hey, why don’t we get together with our friends in Europe, like Spain? And say, “hey, can we struck a deal?”

B: And would the cost of going to Spain to harvest some solar energy and then transporting it back to Germany, would that still be a lot cheaper than building a nuclear power plant?

JM: I expect so, yes. But I’m not sufficiently an expert on that. But I expect so, looking at the cost estimates I’ve seen of the British power plants, my guess is – yes, it would be. Because you would have an economy of scale. The one that we have also now, and that was some of the really impressive figures that were shown in the working group three IPCC report, that came out in April, yeah. They showed just the cost per unit power created and for renewables. And it was just unbelievable how that cost has plummeted over the last 20 years. And as far as I understand, it wasn’t a technological breakthrough. It was just more efficient production because things scaled up.

B: Yeah, well, I guess the demand increased, right? So then it’s easier to get to the economies of scale. My thought would be just with nuclear, I guess, ever since, I don’t know, the 1950s, 1960s, the demand for nuclear has gone down, public opinion has gotten a lot more negative about it. So is that also influencing the fact that the cost is staying so high?

JM: That may be. But I see two other things that would speak against the effect of public opinion. One is, for all I can tell, nuclear power plants are uninsurable. That goes up, no insurance would do that. Because, we know, just look at what happened in Fukushima. There’s an area of several tens of square kilometers, which are de facto uninhabitable. And who would… can you begin to imagine what economic damage that is and that is… no one ensures that. And the other is – no one ensures or takes financial guarantees for what to do with the nuclear waste. If that wasn’t subsidized by the states, it wouldn’t happen, no private company does that. Because we have no idea what the long-term cost of that is. And you can see, look at the agreement in Germany, basically, there was a certain number of billions of euros that the industry paid to the state, but then the risk was transferred to the state. So the public takes the risk for what to do with the nuclear waste. And what to do with highly reactive nuclear waste, it’s completely unclear. No one knows what to do.

B: I feel like I’m totally playing devil’s advocate right now and I’m going going to… 

JM: No, no that’s fine.

B: But I’m just wondering…

JM: Yes, no-no and I think we need to ask these questions. But it’s just that… so it’s an element of risk analysis, of course. And this is one example where I find the use of the precautionary principle adequate. Because if things go wrong with nuclear power, they can go wrong on such a grand scale. And that is different from… and which says that the past is not a good guide, or ever events from the past are not a good guide from what could happen in the future. Whereas, if you take coal, of course, we had many more people dying in coal mines than from nuclear power, that’s true. But we have a pretty good idea of how big the risk can become. With nuclear power, I would claim no, we don’t. And Fukushima is an example. And that there was no big city there. I mean the thought of being… nuclear power, something happening like Fukushima and something happening with a really big city close by. Would we by, in that case… By Tokyo. And the other thing is, and that is something, where some proponents say, “oh, this could never happen in Germany”, they’re always quick to say, after three mile island in Harrisburg, they say, “it could never happen in Germany, ours are built differently”, “Chernobyl, this could never happen in Germany”. Yeah, may be. But what struck me in Fukushima is that, such a high-tech country like Japan, I mean, why did the meltdown occur? Because of the most stupid low-tech error that you can imagine, all the emergency diesel power generators, all drowned in the same hall. They were not protected against the flood and they were not usable. And therefore, the power plant had no power and they could not pull the reactors. And this had nothing to do with nuclear safety design. This just had to do with, could I say, common sense: you don’t put all your eggs in one basket. But they did put all the eggs in one basket so that was a low-tech design error. And they did it. And who’s to say that, in a German power plant, such a similarly stupid mistake is not gonna happen. 

B: Can always happen.

JM: And so I mean, they were so different. Each error was, it was design errors. Some were at a higher tech level. Chernobyl was in a completely uncontrolled experiment, running into the unstable regime of the power plant. Fukushima was stupidity with the generators. And who’s to guarantee that something stupid is not happening… oh yeah, in Harrisburg, they forgot to open the valve for the feeding, for the cooling water feeding. After maintenance, they didn’t reopen. Now, this is low-tech, but it happens…

B: Yeah, it’s stupid that these things happen. 

JM: But that’s the point: stupid things happen. And the potential risk is high. And that is why, I have to admit, I would rather accept a bit more in global warming than having that, to me, uncontrollable risk, sort of, at the tail of the probability distribution. 

B: And actually, going back to the waste, because we were talking about nuclear waste and how we don’t know what to do about it. Actually, so with solar panels though, there’s quite a lot of waste, solar power… especially, because… I’m not sure what metal is in solar panels… I can’t quite…

JM: No, fair enough, a lot of the high-tech products we’re using there, they come with their own pollution problems, no question. And I think we ought to get a lot… we, collectively, ought to get a lot better in reusing, recycling, and whatever. Still, thinking of the waste, highly reactive nuclear waste… and whatever it is that comes out of the solar panels…

B: I will double-check that.

JM: Yeah, I see there is no contest. Because, I mean, I’ve seen a statement recently, someone who was a converted from being against nuclear power, now in favor, said, “oh, after 500 years, it’s no longer dangerous”. And I thought, “well, where does this come from?” and I think, she was referring to the medium-level reactive material. That, indeed, has cooled off after 500 years. But not the highly reactive one. Unless it is being transformed to something else. And that’s a whole new industry.

B: It is, yeah.

JM: Maybe in 100 years, they will have the solution. But even 500 years, safeguarding something for 100 years, I mean we have to look hard to find a political unit in the world that has lasted for 500 years. Of course, China has existed as a state for longer. But, I mean to safeguard something for 500 years – it’s an incredibly long time. And something that’s really dangerous…

B: Yeah. And I guess the same goes for solar panels, like, I think the investment has to go into trying to find ways to take the material out of the solar panels that don’t work anymore, that have expired, basically, rather than just extracting the metals again. That’s really where… because if we can get that right, then it just makes the use of solar panels so much better.

JM: And I think… and that is something where it’s much easier for me to see a solution because we’ve found many solutions for many things. Also when it comes to batteries, we’ve seen…

B: Exactly.

JM: … the cheaper. Again, environmentally – no, not friendly, not usually, there’s work to do. Also, some people say with renewables, “we don’t have the storage”, well yes, but we’re working on it. And people are working on it with high speed all over the world. And we’ve seen the development in the past. And I think there’s good reason to believe it will continue in the future. By contrast, I’ve seen, not in terms of quick development when it comes to nuclear waste, I’ve seen nothing that has been quick. And, of course, there is also the political side – if you look at the history of west Germany, the state and the party that pushed nuclear power most fervently was Bavaria and the Christian Social Union. And if you now look who most determinedly says: “no nuclear waste facility can ever be in our state”, it’s Bavaria. They refuse everything. And so you have this hypocrisy that people don’t want to live with the consequences of their decisions. In this case, the party doesn’t want, that particular party doesn’t want to live for the consequence of their decision. And we can see that that, of course, makes it extra hard. Because they’re not in my backyard, then comes, once people know what they would be getting… and that has to be factored in. But the physics, the pure physics problem of dealing with that stuff is tough.

B: Yeah. So then clearly solar and wind are the way to reach zero here, in Germany.

JM: Absolutely.

B: I also think we should probably make more use of putting wind turbines into the ocean. Just because there’s just so much more wind there, it would be so much more efficient.

JM: Yeah, I don’t know, the thing is the current speed, it’s… or do you mean offshore?

B: Just, I guess, more onshore…

JM: No, do you mean, so to use the ocean currents directly? Or the wind over the ocean?

B: The wind. The wind over the ocean is so much stronger.

JM: Yes, it’s so much stronger. And also I think, and yes, you have less of a problem that people don’t like the sight of them and so on. And of course,  nothing is ever for free, and then, if you install a park somewhere offshore, then, of course, you are influencing ecosystems and so on, that’s true. But I think you’re not getting anything for free. And you’re right, of course, that the wind is stronger. The economic balance is unclear to me because, of course, it’s also hard…

B: To me, as well.

JM: But that is something where I do think solutions will be found. That this can be done. What annoys me is that, especially the conservative parties in Germany, that they blocked the further building of wind power plants in Germany because the distance rules.

B: I heard that. 

JM: Again, Bavaria number one, but Nordrhein-Westfalen, also, where they were blocking, really blocking it. And the installation of renewables has slowed down in the late tens of the century. And I remember, about five years ago, the, then, federal economics minister said: “we’ve got to cap the installation of new renewable power plants I think”. Why? Why we need… was a political goal to cap that? And so it has gone down now. Now it’s disreversing. But to me, it is clear that this is a way to go.

B: I guess one of my final questions would be: how easy is it for you to keep politics and science separate? Because I’m assuming that you talk to politicians as well or, you know, if you were helping with the IPCC, you surely have an influence. And I think that sometimes it can be hard to keep these two separate.

JM: I try to keep them quite separate, one thing that helps me… no, maybe I should start a different way. Someone pointed me to max weber not so long ago so I read a bit of max weber. And I don’t know much about sociological literature but he wrote, in political science, it’s much harder, and he apparently was the first to formulate that explicitly: that it’s a different thing to analyze scientifically how politics work and societies work and to make politics. And what he suggested is: you really ought to keep the object of your desire at a distance. And that’s what I try to do. So that’s one thing. So I try to stay out of concrete political things. I mean, I was asked a while ago: would you sign a declaration against building a coal-fired power plant here? And I said, “no, I’m staying out of these concrete things”. But then, one thing that has helped me is that, of course, people do research on how the politics of climate change, how do societies deal with it, how do social movements operate. And here, in Hamburg, we have an excellence cluster, we call… so funded by the DFG, the German research council, called climate climatic change and society. And I would claim certainly in Germany but I think in the world, we are certainly among the strongest, if not the strongest, in how much social science of climate change we do. Really, the social dynamics. And that has taught me a lot. So these people look at how the public creates narratives about climate change. Because they’re not created by scientists… so the picture of climate is constructed in the social dialogue. And they study social movements: how big is the influence of Fridays for Future, how big is it really? What is it we assume it is and what does it really do? They look at investment patterns and divestment patterns – some of large companies, like, with large CO2 footprints, how do they make investment decisions? Do they change their investment decisions? And so we do a lot of that research in Hamburg. And I’m one of the deputy spokespersons of that cluster, so I’ve learned a lot from them. And what I’ve also done, totally different angle, for many years, with a colleague, I’ve done experiments in the lab, where people play for money.

B: Okay.

JM: And it always has a climate change framing. And so we explore whether people are willing… they can make real money, it’s usually played with first-year students, they can make real money, not huge sums but they play for 45 minutes, an hour, and they can make between, say, 10 euros and 50 euros. And 50 euros for one hour’s work for first-year student, that’s a very good amount, they want to make that money. So we get to their real motives. It’s not role-playing – they want to make that money. They serve their interest, which is legitimate interest. And from all these things, I think I’ve gained, for a hardcore scientist, I would say I’ve gained a pretty solid understanding of political processes. And so I am looking at the political process and the social discourse and I try to understand. And then I would comment on what works and what does not work. And so I would say, I’m staying out of the day-to-day politics but I do look at what has happened. And then a colleague of mine here, from the social sciences, she actually said, a year ago, “well, you’ve changed your tune”. Because I’ve been asked, in an interview, “what can I as an individual do to prevent further climate change?” and said, “look, of course, there are these things that are sensible: less car usage, more public transportation – but that’s not going to change the political system and we need to change the energy transformation, we need to transform the energy system. But the one thing I believe you can do is: make sure people run ministries who take climate change seriously”. And in the old government, we have an economics minister and we had a transportation minister, who did everything in their power to block, to prevent climate change. I would still claim that was an analysis of the political system. And I think what we see now, even if people are not always happy with what the government does, but we’ve seen a huge improvement through this changing government. I’m a lot more optimistic now than I was before. So now you could argue – was I being political? Maybe I was but it’s also, I would say, it’s an analysis of the political situation, with a minister who doesn’t care or is unable, this is not going to work.

B: Yeah, that’s very true.

JM: And it may be almost a truism but still: the ministers are powerful. And we see, especially in Robert Habeck, we see that fantastic change that has taken place at the level of that ministry. So I’ve done that, so in that sense, I am not, I’m certainly not sitting in the ivory tower. I still try to acknowledge that the scientific analysis and the scientific result, even a scientific analysis of the political system, is something very very different from making politics.

B: Yeah.

JM: But I probably am a bit more forthcoming now in speaking my mind. Because I, in some way, I did get fed up. Certainly, I got fed up with that old government.

B: Yeah. I mean, I think it’s very important for scientists to speak their mind and make the narrative. It is our job to do that as well. But it’s just… I do feel like climate change is a topic that is very scientific but very politicized these days. 

JM: And the difficulty is, I certainly do not want to come across as an activist, that the difficulty is, I think, with activism is that… of course, some people have to be activists, of course, political change only occurs because they’re active, no question. But mixing the roles of a scientist and an activist, the fear I would have is that I underestimate the possibility that I’m wrong scientifically. And I got to be open for that. And if somehow being right means it serves what I like to see to be done politically, that’s when I’m getting sceptical. Am I as willing, I mean it’s always hard to admit I’m wrong, I was wrong, it’s never easy for a scientist, or anyone else, but also scientists. We always say, “oh yeah, new evidence comes in and we revise our statement”. Come on, it’s not that simple. Everyone who’s doing science knows that it’s not true. But I think it’s harder still if you suddenly say, “oh, it would be better if I was right because that helps this cause”, that’s getting dangerous. And so that’s why I think distance to the object of your desire is an important thing to increase chance of being self-critical enough.

B: Yeah.

JM: But I have no recipe for where to draw the line. I mean, I think we as a field have an obligation to engage in the public discourse, no question. Whether, would I be in favor of building this or that LNG terminal? That I find difficult. And there’s also the question: do I have the knowledge. And also I see a number of quick transfers of scientific analysis, especially in economics, into political demands, where I feel quite uneasy, I’m gonna say, I don’t think that your theory carries you far enough to place this demand.

B: Yeah. Well, thank you so much for this really nice conversation! I really enjoyed it! And yeah, thank you again.

JM: Thank you! I enjoyed it too.

B: That’s it. Thank you all so much for listening. If you would like to learn more about professor Jochem Marotzke and his research, you can check out his website. And if you like our podcast – make sure to follow us on Twitter, LinkedIn, and Instagram. Thanks again for listening! Bye!

Offspring Magazine the Podcast is brought to you by the Max Planck PhDnet Science Communication Group, known as the Offspring magazine. The intro-, outro- music is composed by Srinath Rankumar. And the pre-intro jingle is composed by Gustavo Carrizo. Give any feedback, comments, or suggestions, please feel free to write us at Until next week! Stay safe, stay healthy, bye!
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