Kimberly White
Hello and Welcome to Common Home Conversations. Today we are joined by renowned climate change expert and earth system scientist Will Steffen. Will is an Emeritus Professor with the Fenner School of Environment and Society at Australian National University. He also serves as a Councillor with the Climate Council of Australia and as Co-Chair of the Scientific Committee of the Common Home of Humanity. Thank you for joining us today.
Will Steffen
My pleasure.
Kimberly White
So Will, what does it mean to be an Earth System scientist? What are you currently focusing on?
Will Steffen
Well, an earth system scientist is someone who studies our home planet but studies that as a single, integrated system. And that's a relatively new area of science because the natural sciences, in general, likes to look at pieces of a system, pull them out and study them in great detail. Whether it's pieces of an ecosystem or part of the climate system, you might be studying what's happening to the ice sheets or what's happening to oceans circulation and so on. And so that's the way natural scientist has worked for, for decades and centuries. But in fact, a new area of science called complex system science has been developing, trying to put the pieces back together and understand how systems work as complete systems. And they have things like emergent properties, things that you can't understand just by looking at the pieces of the system in isolation. So now we're applying this sort of thinking to the earth as a whole. And we call it the Earth system because, in fact, it has properties that are characteristic of the earth as a whole. And it has processes which change these properties. Now, in a practical sense, that means that as we look at the earth system today, it's changing very rapidly. It's moving away from an 11,700 year, very stable state, which we call the Holocene or the geologists call the Holocene, and it's moving away from that at a very rapid rate because of human pressures. So we're trying to understand what is it that is driving these enormous changes. And there are many interesting ideas here. One of the most important ones, though, are tipping points, which are parts of the system. When you push them, they appear to be resistant to change; when you push them just a little bit too far, they can flip or move into another, another state. And some of these are linked to form what we call tipping cascades. So this really is, if you like, is the engine that's driving changes to the earth system. So we need to understand low, gradual changes. But we also really need to understand how these tipping points may lead to more rapid change and changes that will be very, very hard to reverse. So just again, in summary, what Earth system scientists try to do is we're trying to understand our planet as a single complex system, one that has its own property. At the planetary scale, and one which is being pushed very hard by human activities. So basically, that's what we're trying to do.
Kimberly White
That is very impressive- sounds like a fascinating field of study to be in. I know that there are some in the scientific community that have stated we have entered the Anthropocene due to the building pressures from humankind and you mentioned tipping cascade points. Can you elaborate further on this?
Will Steffen
Yeah, I can give a common analogy in everyday life is if, say someone goes out on a lake with a kayak and is paddling around, you can jiggle that kayak a little bit, then it returns in its upright, you can paddle alone. But if you tip it too far, it flips all the way over, and you're underwater, and you've got a scramble to get back to the surface. And that's a tipping point, almost literally, you've tipped it past the point of no return, and the kayak flips. So that's a very simple analogy toward parts of the earth system, which simulate similar behavior. A good example of that might be the sea ice that is floating over the Arctic Ocean. So how does that work? Well, in the Northern Hemisphere, summertime, there's a lot of sunlight over the Arctic Ocean. But if it's covered with ice, that white ice reflects the sunlight, affects virtually all of it and helps keep it cool. But as the earth is warming that summertime sea ice is shrinking, it doesn't cover as much of the Arctic Ocean. So as it shrinks, it uncovers darker ocean water that absorbs more sunlight, obviously than the ice does. And it adds to the regional warming over the North Pole. And of course, as the North Pole warms more, the ice shrinks more. And as the ice shrinks more, it warms more. So you see what we call a feedback loop. So a lot of these tipping elements have these feedback loops. And the point here, what's the tipping point? The point is once the ice shrinks far enough, you cannot stop the process. In other words, that feedback loop will take it all the way to an ice-free Arctic, no matter what we as humans do. So that's a good easy to understand example of what a tipping point actually is. There are other ones associated with ice, too. If you look at the Greenland ice sheet, that's that big massive mound of ice that sits on top of the island of Greenland, that's starting to melt, and it's melting at an increasing rate. And one of the important processes there is that as it melts, it gets lower. And as it gets lower, it moves into a warmer climate, which makes it melt more, and then it moves even lower. And you can see again, you have an internal feedback that this is going to cause the ice sheet to diminish very rapidly no matter what we do. I'll give you one more example of an individual, a tipping point one that isn't associated with ice. And that's the Amazon rainforest. That's that big rain forest, beautiful forest in the Amazon basin, the biggest tropical forest on the planet, but that is now being threatened by two interacting processes. One is direct human deforestation. And that's obviously involved with politics. It's involved with globalization, big investment companies investing in deforestation and conversion to soya or beef, or so on. And what that does is it reduces the recycling of water in that system. So basically, as the name indicates, it's a rain forest. So it needs a lot of rain to be a healthy forest. This rain comes from two sources. One is evaporation from the forest itself; it's got its own recycling system. So roughly half its rainfall actually is generated by the forest itself. The other half comes in from the Atlantic Ocean, so it's moist climate weather systems rather than come in and drop rainfall. So it's about 50/50. So as we deforest, more of that tropical forest, we are reducing the amount of internal recycling of water via the evaporation from the forest. At the same time, the Atlantic circulation is changing because of climate change. And that's reducing the rainfall coming in from the ocean. So the Amazon forest is hitting a double whammy. So it's going to hit a point where it doesn't get enough rain, it starts burning more often, that reduces the internal cycling even more. And it becomes a self-reinforcing feedback again, this idea of a feedback that will convert the forest or most of it into what we call a Savanna, a sort of woodland grassland, much drier system. So there are three examples of what tipping points are, what internal feedbacks are. Now, the word cascade comes in here too. And that's because a lot of these individual tipping points or tipping elements are actually linked. And the ones I mentioned are actually a good example of that. Because as you lose more Arctic sea ice, it causes regional warming, regional warming i...
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