2.13

## University of Bergen

Skip to 0 minutes and 5 secondsWelcome to week two of our course Causes of Climate Change. Today, were going to give you a bit of feedback based on the questions you submitted. My name is Kerim Nisancioglu. And I'm Asgeir Sorteberg, and together with us today, we have our student Nadine, and she has picked out some of the questions that a lot of you have wondered about in week two. So Nadine, what is the questions we're trying to answer today? Yeah, hi, I am Nadine Steiger, and I've have just finished my master's in climate dynamics. And in this course, I'm your mentor together with Ida-Maria, and we're trying to help you through this course.

Skip to 0 minutes and 45 secondsSo the first question is about the topic on climate feedbacks that we had in this week. So there we calculated the change in temperature by adding up to different various climate parameters. But there are so many feedbacks, and these parameters, they're coupled together. So Asgeir, could you explain us if it's even possible to just add up this different parameters. Well, thank you. I'll try to take a brief explanation of this on the blackboard.

Skip to 1 minute and 20 secondsSo the question was, can we really add these feedbacks together? And the answer to that is no, you cannot really add them. They are not linear in the way that you can add them. They actually interact with each other. So in reality, it's a bit more complicated than what we try to explain in the course. So I'll just try to give you an example. What we did in the course was say that, if you had feedbacks here, feedbacks, we just said, if you have one feedback, you could add it to another and so on, all right, without them being interacting with each other. So the strength of them was independent of all of the strengths of the other feedbacks.

Skip to 2 minutes and 0 secondsBut in reality, they actually-- the strength of them are connected. So let me take an example here. If you have a temperature change-- and this will make, for example, a change in the sea ice. All right, so we have ... sea ice here, sea ice, which again then will change the reflectivity, which again will change the temperature. This is what we call the albedo feedback, all right? And on the other hand, we maybe have another feedback like the cloud feedback, which will be that, if you have a change in temperature, that will also change the amount of clouds.

Skip to 2 minutes and 46 secondsAnd the amount of clouds will again change the reflectivity, which again will change the temperature. So these are two separate feedbacks now, but they interact together. So for example, if you change the sea ice, for example, you will change the evaporation, right? For example, if the sea ice disappear, you have a lot of open water, you will have more evaporation.

Skip to 3 minutes and 14 secondsThat again will then change the clouds. So you see that the two are connected together, and that's just one of several examples that feedbacks are closely tied together, and they're not really separate. And that... and that's one of the reasons why we have to make complicated climate models, to actually answer the question which feedbacks are most important. Yeah, thank you very much, Asgeir, for this really nice explanation. So we also-- in this course, we also discussed the relative role of the ocean versus the atmosphere when it comes to transporting heat towards the poles. And we discussed the Gulf Stream, which causes higher temperatures in Western Europe compared to other areas at the same latitude.

Skip to 4 minutes and 3 secondsSo Kerim, could you please explain why, then, we say that the atmosphere is more important in transporting heat towards the poles. OK, yes, thanks. So this is a key question that comes up very often. And the thinking is that the ocean and the Gulf Stream is really dominating the climate of Western Europe, and that's why it's so warm here, both in the winter and also a little bit milder summers. And in particular, you can see this in Bergen where it's quite mild winters and relatively cool summers. And we think this is due to the ocean, but it's not the full story. So I'll explain a little bit more in detail.

Skip to 4 minutes and 41 secondsSo if we draw a map, and with my beautiful skills and in drawing, this is Greenland and this is Norway. And Norway and Europe here are-- has a big North Atlantic Ocean to the west of it. In the ocean, there are what we call ocean gyres, and these gyres are rotating like this in the north. That's the subpolar gyre. And then down here, you have what's called a subtropical gyre, which rotates in this direction. Between these, you have the Gulf Stream, and it goes something like this. This is one of the pathways for warm water from the tropics, or the Caribbean even, up to the coast of Europe, and in particular Norway. But this is only part of the story.

Skip to 5 minutes and 31 secondsSo the main circulation in the ocean is due to the subpolar gyre and this subtropical gyre. And these are the ones who mainly transport mass, and the Gulf Stream is a minor component of this. So the big players in circulation in the ocean are the gyres, and those are wind driven. So these wind driven gyres transport most of the mass in the ocean, and then you have this smaller part, which is a Gulf Stream. But it's warm, and for sure, it brings heat in towards the coast of Norway.

Skip to 5 minutes and 59 secondsBut if you were to shut this down-- and there have been experiments doing this, actually turning off in a climate model, the component that transports heat to the north-- it doesn't make a huge difference for climate in Europe. And that's because, over this area, you have very strong westerlies and storm tracks, so these bring a lot of moisture and heat to the continent. And these hit pretty much the west coast of Norway and Bergen, where we are. And that's one of the reasons it's so wet here, but it's also one the reasons why it's so warm here compared to, for example, Greenland or Canada, which is at the same latitude.

Skip to 6 minutes and 40 secondsSo part of the story is that the ocean is warm, but the main player here is still the winds who transport a lot of this heat from the ocean onto the continent. So you have to see these two together. And for high latitudes, the atmospheric heat transport dominates. And I think we have a bit more-- there's a bit more to this story that, actually, Nadine, you're going to explain, right? Yes, I will try to do that. So Kerim has just explained why there is a temperature difference at one latitude because of the ocean currents, which makes Greenland, for example, much more colder than Norway.

Skip to 7 minutes and 19 secondsBut he also mentioned that the west coast of Norway, it's a much smaller seasonal variability compared to further inland, and I will try to explain that. So at one latitude, the mean temperatures at the coast compared to the inland may be very similar. But if you look at the annual variability, the temperature along the time from January to December can look along the coast, it may look something like this. So it's cold in winter, and it's warm in summer. But when we go further inland, the variability looks more like this, so it's much colder in winter and it's much warmer in summer. And this has to do with that we have the ocean versus the land.

Skip to 8 minutes and 25 secondsSo the ocean needs much more time, and it's much less efficient, in heating up when it gets heated up by the solar radiation, and this has four different reasons. So the first one is the heat capacity, and this is about 4.2 for water, but it's only about 1.8 for land. So the heat capacity of water is more than four times as large as the one for land. And that means that, if you want to heat up one kilogramme of water, if we want to heat it up by one degree, then we need four times as much energy as if you want to heat up one kilogramme of land by one decree. The second effect is the transmission.

Skip to 9 minutes and 29 secondsSo we all know how that water is more transparent compared to land, so the sun rays, they can travel much further in depth compared to land. In the ocean, therefore, the sun energy, solar energy, is being spread over a much larger volume compared to on land, where it only heats up the surface. The third point is motion.

Skip to 10 minutes and 2 secondsThe ocean is in motion all the time, due to currents and eddies. So the warm water at the surface gets mixed up with deeper layers, which are colder, and then the surface gets cooled by these deeper layers, whereas the land cannot mix as well so the heat just stays at the surface.