Welcome this is the feedback video for week 3 of our course, Cause of Climate Change. We very much appreciate you all following us over the last three weeks, and interacting with you on the online discussion forums. We also had a few students here in Bergen following the course. We had a lot of interactions with them, and I’ve picked up some questions, both from the discussion forums and from the students here in Bergen, and I’ll discuss this with you today. I’ll start by discussing a little bit the concept of ocean circulation and deep water formation as this is something that several people have been asking about.
As you might remember, this figure which is in the MOOC, actually from week 2, but it also relates to heat uptake which we discuss in Week 3. Basically, this is showing the ocean circulation in the model trained by data. It’s pretty much the real circulation as it is in the ocean, with all the details, all the eddies, the large-scale features like the Gulf Stream and the Kuroshio off Japan, the Agulaz rings. In the Southern Ocean, I don’t know if you can see this, there’s also the Antarctic Circumpolar Current. So one of the questions we have, is where does all the water that downwells, or sinks go?
For example, in the North Atlantic, and in the high latitudes here off the coast of Norway, there’s quite a bit of deep water formation because the worm Atlantic Current, the Gulf Stream, brings with it heat from the Caribbean and releases its heat to the atmosphere. And eventually the water is dense enough and sinks to produce deep water, and returns south as a colder current - into the Southern Ocean. Now in the, and just to complete this, you can see the Gulf Stream transports the warm Atlantic water to the north. Now, there is upwelling in large parts of the ocean. There’s mechanical stirring that brings the the deep water up to the surface.
But this is a slow process and can takes hundreds of years, up to thousand years. So, these currents bring the deep water and distribute it into the deep ocean, where it eventually joins and enters into the Pacific. And so you have deep water going also into the Pacific and into the Indian Ocean. But this deep water, through tides and through mixing across ocean ridges and so forth, this water is mixed and it’s also brought up to the surface eventually. Both in the tropics over larger areas, and also upwelling in regions along the coasts with very good fishing - these regions along the coasts of South America, parts of Africa and other places in the World.
But there’s also quite a bit of upwelling in the Southern Ocean, and this is due to the strong westerly winds. These westerly winds blow from west to east and it’s quite a tough place to sail because of these strong winds, but that’s also where you mix and bring a lot of deep water up close to the surface, and you’re also ventilating the ocean in these regions. This is a very important part of the oceans where we have love of deep water ventilation. All right, so that’s just a little recap of deep water, deep water circulation and ventilation.
And then we move on to another topic, which was also a question that we had from both some of you out there, and also from our students here in Bergen - this is tipping points. I can also recommend a course by Tim Lenton from the UK on FutureLearn which relates to tipping points in climate change. This is a topic that’s been discussed quite a lot in in our field.
concept is maybe known to several of you: Once you push a system hard enough, you can end up in a different state. So you go from one stable state, let’s say the current
interglacial is one state, right: It is relatively warm, there’s not much ice, except for on Antarctica and on Greenland, there’s not much ice on land. If you push the system hard enough you might enter a glacial climate. Right, so depending on how close you are to this transition to a different climate state, i.e. the tipping point, you might need a very small push before you go over into a different climate state. For example, this could have been a glacial climate and you have the slow gradual change in the insolation, eventually you will reach a tipping point, and glaciers start growing.
More ice, and through all of these feedbacks we’ve learned about in week two that accelerate the process and you get a glacial. So that can be thought of as a tipping point. But what other tipping points do we have in the climate system? And could we approach them now in the future? This is a recap of one of the figures, or animations, that I showed you in Week 1. Basically what do we expect in the future, as the climate is changing? So, we’re going into a warmer climate. There are two different
SCENARIOS HERE: there is the business as usual on the left, which is kind of pessimistic with a lot of man-made emissions of greenhouse gases just continuing for the next many decades; on the right is more optimistic, where we curb burning of fossil fuels and our emissions of greenhouse gases. So, now, what path we choose is very important in terms of if we approach a tipping point in the future. So the one on the left is the pessimistic one, and the one on the right the optimist one. The one on the right, we assume is safe, right so we’re within the safe operating spaces of the climate system. So this is
NOW SHOWING THE TIMELINE: the historical in black. You’ve seen this several times before. Then you have the red and the green with two different scenarios. These are RCPS from the IPCC report, the climate report. You can see that one of them goes to five degrees global warming, the other one goes to below two degrees global warming. What is the safe operating space? And what are potential tipping points we might cross, if we approach for example the red line here, which is the the pessimistic scenario, where we keep emitting a lot of greenhouse gases and climate warms a lot? Where if any point in the next decades will could we reach a tipping point in the climate system?
And thereby also have cascading effects that would be hard to stop, or sometimes not possible to stop? So if we look at, well let’s just use this figure for reference, it’s a beautiful figure, or animation made by my colleagues at MIT.
Where are the challenges, the alarming changes that might pose a risk of crossing a tipping point? So we have Greenland. You’ve learned that Greenland is covered by ice. Well we know that. You’ve seen pictures from there. We also have Antarctica. We have glaciers in the Alps and the Patagonian and the Rockies. I won’t talk much about that. The Greenland and Antarctic ice sheets are ice masses that have been stable for thousands of years. And they change on glacial timescales, but in the last many hundred years, at least, they haven’t been very big changes in these ice masses.
Well we know that if you go 120 thousand years back in time for Greenland, a large part of the ice there or a significant amount of ice there was melted and therefore the sea level 120,000 years ago was 2 to 4 meters higher - maybe even more. Maybe you have to double that. And the climate wasn’t very different from today. It was more like, okay, two to three degrees warmer at high latitudes of the northern hemisphere. And this was due to orbital differences, but also some feedbacks relating to the composition of the atmosphere could have been relevant, but less so.
So the calculations that we have, and I could have shown you some figures, but I didn’t bring them with me here and now, but if you approach two to three degrees this is where we expect the Greenland Ice sheet, for example, will cross a tipping point and melt. And it will be very hard, if impossible, in the next thousands of years to bring it back. So we’ll start the melt, but it will take a long time. But it’s unstable, already showing signs of being unstable. And the current one degree warming is what we have today, but that’s the global average. On Greenland and in the high latitudes of the Arctic that’s more like two degrees today.
So Greenland is very close to a tipping point, and it will be passed a tipping point within this century - if we go for the scenario of continuing our emissions of fossil fuels. Antarctica will take longer, but for the Antarctic Peninsula, which is this part here, there are already signs of glaciers like the big Larsen ice shelf - so these are the floating parts of the Antarctic ice sheet. But maybe also West Antarctica, which has a large part which is below sea level, could be vulnerable if we go above 2 degrees global warming. Other tipping points that are important. - tipping elements of the climate system: For example the Amazon rainforest.
We’ve seen also human impact, not only through warmer, maybe drier climate - which is not good - We also have seen deforestation. If you have all of these things effects, compound effects, coming together, eventually you You could cross a tipping point, and it would be a very different ecology in these regions, which are now this important rainforest which are important for the species richness and also for local climate. So you can cross a tipping point where the Amazon rainforest not stable anymore. So this is a region to be aware of. I can mention here that the Sarah was actually green three-four thousand years back in time.
So there are periods where we have examples where there are big changes in the land vegetation. Another key thing is the permafrost - both on land - but also on the continental shelves in the Arctic region. These are thawing. Also in the ocean there’s methane. In permafrost there is methane. In the ocean the methane is stored in the sediments - it’s frozen as clathrates. And this, when it gets warm enough, willl start bubbling up to the surface. And it’s a very potent greenhouse gas. So there you can cross a tipping point where you have large amounts of methane being emitted to the atmosphere, and therefore you have a strong greenhouse effect. Then yeah, you have these feedbacks ticking in.
So those are some of the key tipping points in
THE CLIMATE SYSTEM: ice, rainforest, permafrost. Coral reefs in the ocean. The ocean absorbs most of the co2 we emit to the atmosphere and it becomes more acidic and you also dissolve, bleach, these corals. This has massive consequences for coral reefs worldwide in the ocean. It has already. And is another tipping point in the climate system. One that we have discussed and I won’t talk too much, is the Gulf Stream and whether you can have a freshening of the surface ocean. Because of melting the Greenland ice sheet, you could have less deep water formed in the North Atlantic/Arctic and therefore less or weaker Gulf Streams That’s not necessarily true.
It will be one of the major changes for the climate locally, but it definitely is a potential tipping point as well that has been discussed a lot in literature. All right so I can easily be carried away talking about this topic. I’ll leave it for now and rather provide some extra literature. If you have more questions please write them into the FutureLearn discussion forums. We’ll try to monitor and be available for some time still. But for all of you I would very much like to thank you for following our course. Also on behalf of Jonathan and Anais working with you sonline.
I know these are special times and circumstances so we very much appreciate that you use your time to follow this course, and I hope you have a very good learning experience together with us over the last three weeks. So keep it up! If you’re not finished - just keep going and we’ll be following you online. That’s it from here - thank you!