Skip to 0 minutes and 5 secondsHi, and welcome to this the feedback video of week three, of the course "Causes of Climate Change." My name is Asgeir and today Kerim couldn't join us, so instead I brought Mari with me. Hi. This week has been great, as have all the other weeks. We've had a lot of discussion in the discussions forms, and we're very grateful for all the questions and comments you've had. Today we have Omar and Sunil with us, and they will be asking us some of the questions that you have had this week. In degrees and the records of the past climate change, there was a question-- which are the main drivers of the climate over the past 2,000 years?

Skip to 0 minutes and 44 secondsA lot of our students are little bit confused would this question, so Mari, can you explain which is the best answer to this question? Yeah. We've seen that this question was maybe a bit badly formulated, so we apologise for that. We've see that it's cost a lot of confusion. So I can just go through the different answer. The first alternative of the quiz which was changes in the orbital parameters of the sun, that is supposed to be wrong. And it's wrong in the quiz, because the changes in the orbital parameters are of a thousand yeah timescale-- or 10,000 years timescale, while we are looking for the main driver of climate change in the past 2,000 years.

Skip to 1 minute and 23 secondsAnd hence the changes in the orbital parameters, they're just too slow to be changing the climate a lot over a 2,000 year time. For answer number two, that was correct. So that was changes in volcanic emission and CO2, am I correct Sunil? Yes, perfect. Then answer number three, I think that was the one that caused the most confusion. The alternative was changes in land use and the release of methane, and we said in the quiz that that was wrong. So we were asking for the main driver of climate change. And changes in land use, while that is changing the climate, it's a very small effect-- at least a direct effect.

Skip to 2 minutes and 8 secondsSo the direct effect of changing land use is changing the reflectivity of the land, and this is not causing a big climate change, but yeah, to some degree. So this could be a correct answer, depending on how you define the main driver. And also release of methane is also drive growth of climate change. So we apologise for this answer, which some of you thought was right, and I would also say, yes, it could-- this is the right answer. So if you had that, everything down, then you are correct. And then the last answer, what was that about, Sunil? It was in the number of sun spots and the brightness of the sun.

Skip to 2 minutes and 47 secondsYeah, so this is also a driver of the climate change in the past 2,000 years, and this question it seemed like you guys already got. So I hope this helped with the confusion of the quiz number four, and that you now see what are the main drivers of the climate change in the past 2,000 years. In the last climate change article, there was an upswing in the CO2 concentration-- variation over the different glacial and interglacial time periods. So can you explain why we have such a large variation in the CO2 concentration in the past, and how it's different from the current CO2 trend? Yeah.

Skip to 3 minutes and 29 secondsSo CO2 has changed with temperature throughout the glacial and interglacial cycles, and this CO2's change is more often of a response to the temperature increase. So when the climate has gone toward an interglacial climate, CO2 has been released from the deep ocean, probably due to a warming of the ocean. This increase in atmospheric CO2 content has then amplified the warming, and that is consistent with the glacial climate. So the CO2 that's varying with the temperature is actually acting as a positive feedback to the temperature increase. So CO2 is a very possible mechanism to have brought the glacial climate.

Skip to 4 minutes and 9 secondsAnd we do see that going out of an ice age is much more rapid than going into an ice age, and CO2 is probably a big driver of this fact. Now this increase in CO2 has a much longer time scale than the climate change time we're seeing today. So the time scale is about 200 to 1,000 years, and it's also incorporated in climate models. So we are quite sure that the CO2 changes we're seeing today is not the same as the CO2 changes we were seeing during the glacial cycles. CO2 is a major component of our climate system. How can one be confident in CO2 measurements? And how can we get global averages of CO2 from locals parts measurements?

Skip to 4 minutes and 57 secondsThank you Omar, that's a great question. And that we have good instrumental records of CO2 in the atmosphere back to the 1950s. In the 1950s we got a new measurement method for measuring CO2, using spectroscopy. And before that, we had some measurements that were made with chemistry, and which were very unreliable. So we only have really good data from the 1950s and onward. And the second part of the question, how can we get the global average when we only have a few point measurements? Well, the reason for this is that CO2 has a very long lifetime. So now we have observations all over the world, showing almost the same concentrations.

Skip to 5 minutes and 43 secondsSo if you release some CO2, for example, in the northern hemisphere, it will mix in a few years time and you will have almost the same concentration in the southern hemisphere, just a few years after. It's actually quite easy, even if you only have a limited number of stations to make a global average, because CO2 is so well mixed in the atmosphere. When describing the ocean heat uptake, you talk about effective heat capacity. Can you please tell us what is the difference with the specific heat capacity? Yeah, great question Omar. So the specific heat capacity and the effective heat capacity are closely linked. So I start with the specific heat capacity.

Skip to 6 minutes and 25 secondsSo the specific heat capacity, that's the amount of energy you need to warm up one kilogramme of mass with one degree. So let's have that first. We said specific heat capacity-- we call that Cx. And so that's in the units of joules per kilogramme per Kelvin. So that's the amount of energy needed to warm up one kilo with one degree. But in climate science, we'd often talk about the effective the heat capacity, and it might be a little bit confusing. And it's also confused me, actually, in the beginning, but I'll try to explain what we mean.

Skip to 7 minutes and 12 secondsSo if you have the surface of the ocean here, and you impose a radiative force in, for example, a change in the greenhouse gases or changing the role in the solar radiation, and then the ocean will start to heat. And let's say after a few decades, maybe the heating has gone down to this level, which have a certain depth. We call that d1. So now the effective heat capacity-- that will be the specific heat capacity. So if we call that the big C, that will be the specific heat capacity times the density of the ocean, times the depth of where there has been a warming.

Skip to 7 minutes and 53 secondsAnd let's say a few decades later, the warming has penetrated deeper in, maybe to this layer. And then certainly the depth have increased. So that means that we will have a new effective heat capacity, which will be the specific one times the density, times the new depth where the heat has penetrated down. So the effective heat capacity is changing with time as you get the warming deeper and deeper into the ocean. So that is what we in climate science is calling the effective heat capacity. So that was the feedback video from week three. We hope we managed to answer some of the questions you have had, and that you are a bit less confused.

Skip to 8 minutes and 37 secondsAnd this is also the last week of the course, so I will use the opportunity to thank you all for participating in this course. It's been a joy for us to follow you, and we really hope that you have enjoyed the course. We know that there's been challenging. There's been some maths. There's been some physical concepts that's been hard to understand, but we really hope that you have gotten a grasp on what climate science is all about. It's about the physics of nature. And we really hope that you want to learn more about this. So thank you everyone for joining us, and we hope to see you in some later course. Thanks.

Week 3: feedback

In this short video the educators meet a group of University of Bergen students, discussing some central questions from this week’s lessons.

The main questions discussed in this video are the following:

  • What are the main drivers of climate over the past 2000 years (follow up to quiz 3.3)

  • Why are there large variations in atmospheric CO2 concentrations in the past and why is this different from the recent observed trend?

  • How do we measure atmospheric CO2 and have confident are we in the accuracy of these measurements?

  • What is the difference between effective and specific heat capacity (relates to video on ocean heat uptake)?

Questions from all learners - posted througt the “FutureLearn - Comments” were considered for the feedback sessions.

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This video is from the free online course:

Causes of Climate Change

University of Bergen