Planetary Wobble

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Speaker 4 You're about to listen to a brand new episode of Curious Cases. Shows are going to be released weekly, wherever you get your podcast.

Speaker 4 But if you're in the UK, you can listen to the latest episodes first on BBC Sounds.

Speaker 4 I'm Hannah Fry. And I'm Dara O'Brien.

Speaker 2 And this is Curious Cases.

Speaker 4 The show where we take your quirkiest questions, your crunchiest conundrums, and then we solve them. With the power of science.
I mean, do we always solve them? I mean, the hit rate's pretty low.

Speaker 4 But it is with science. It is with science.

Speaker 4 You know, last year, I was filming a travel series. And so I was away for all of winter.
I missed winter.

Speaker 4 And I hated it. Oh, really? A year of summer.
It was horrible. Oh, that's interesting.
I've been craving this winter for well over a year. For what part?

Speaker 4 What does it fulfill emotionally or psychologically? Snuggliness. Oh, so just, yeah, you just want there to be some sense of, here I am batting up the hatches against the cold.

Speaker 4 Also, just like relieving you of the pressure that you feel like you should be outside, you know?

Speaker 4 I'm sitting here and reading a book and that.

Speaker 4 I'm not going to judge myself for it. Yeah, I mean, that is one of my major things during the summer is about four o'clock.
I always go, wasted another day there.

Speaker 4 There's only a limited number of these. And I didn't go out in it.

Speaker 4 There are some places where it's just constant, constant, happy sunshine. Absolutely.
There are awful places. There are awful places filled with terrible people and there's no internal life at all.

Speaker 4 Yeah. So I was just saying, it's a Sydney-Melbourne thing in Australia where Sydney's really sunshiny and everyone's

Speaker 4 all the time. And Melbourne has loads of theatres.

Speaker 4 Loads of theatres. I mean, because people are driven indoors.
Correlation is not always causation. It clearly isn't.

Speaker 4 Sometimes. Yeah.
I mean, it really is quite the broad stroke, I'm sorry. So what we're saying is the only reason why we have art is because we've got seasons.

Speaker 4 I think that's a big thing. I think people were driven indoors.
You've noticed that cave paintings are in caves because people were sheltered from the rain.

Speaker 4 Nothing to do. They didn't paint them outside.
Are we saying here that we like both? Is that what?

Speaker 4 It may be a very long roundabout way to say that this has worked out very well. It's worked out very well.
Yeah. Because there's a very particular reason why we happen to have both, Dara.

Speaker 4 And it ties in very nicely to the question that we have today that came in from Andrew who sent an email to curiouscases at bbc.co.uk.

Speaker 5 G'day, Dr. Fry and Mr.
O'Brien. Hope you're keeping warm as the dark and cold winter approaches.
My name's Andrew and I live on the Morning Peninsula south of Melbourne in Australia.

Speaker 5 It's nearly summer in the southern hemisphere and the days are getting longer and warmer. This daily change happens because the Earth is wobbling on its axis.

Speaker 5 It's this wobble that produces the seasons and the weather patterns on Earth and the rhythm of life is set by this yearly cycle. But what if there was no wobble?

Speaker 5 What would the climate and weather be like at various latitudes? Could life have even started without this wobble?

Speaker 5 Are we all children of the wobble?

Speaker 4 I think he, it's only the Australian accent that meant he said the word wobble as much as he did.

Speaker 4 Because actually, is wobble the right word? I don't think it's the right word. I think wobble feels like jelly, wobble feels like something random, and whereas this is really predictable.

Speaker 4 I mean, basically, there is a plane on which we travel, but we spin at an angle to that. Right.
So, and not all planets do this. So, we spin at an angle to that, 23 degrees specifically.

Speaker 4 We're off the ecliptic, which is the line that the basic plane on the planets going around the sun.

Speaker 4 But it means it kind of shares it around, if you know what I mean, shares the sunlight around the planet. So that's kind of what this means.

Speaker 4 So we wobble in the sense that different parts of us are facing the Sun at different times because of this 20 degrees degrees angle. But we don't wobble in the sense of like, oh,

Speaker 4 which way is it going to go? And it's suddenly going to settle down or it's suddenly going to stop wobbling. That's not going to happen.

Speaker 4 I can imagine if you were viewing Earth from sort of outer space, right? Like the perspective of some sort of giant alien being,

Speaker 4 it would look like a spinning top, which is sort of sometimes pointing towards the sun, sometimes pointing. That would make sense, yeah.
That's a bit wobbly. So the tilt.
Yeah, it's predictable.

Speaker 4 It's not about to stop. I just want to reassure people why it's not about to stop.
But it is a great question. Isn't it, right?

Speaker 4 Because what if you took that tilt of 23 degrees and made it so the Earth was sitting absolutely bolt upright in its path around the Sun? I mean, what difference would that make?

Speaker 4 Apart from the fact that we've already scientifically proved there would be no culture. Yeah, yeah, yeah.

Speaker 4 Just from the K-Pennies on, there'd be nothing. There'd be nothing.
Nothing Nothing at all. Nothing at all.

Speaker 4 Well, okay, if we want to take an actual scientific approach to this, thankfully we have some experts on hand to help us straighten things out.

Speaker 4 Joining us in the studio, we have evolutionary biologist Professor Rebecca Kilmer from the University of Cambridge and climate modelling researcher Dr. Robin Smith from the University of Reading.

Speaker 4 Now, Robin, I know that you ran a simulation to see exactly what would happen if the Earth sort of

Speaker 4 lost its tilt and was instead bolt upright. How How did it change? What was the difference?

Speaker 6 So for the range of things that we included in the model, which wasn't everything, what we found was there was a big expansion of sort of glaciated regions, big expansion of the deserts in the mid-latitudes, but overall there's a lot fewer areas that are suitable for life.

Speaker 6 And you don't have any seasons, obviously.

Speaker 6 Basically, as we go around the Sun, the fact that we're tilted slightly more towards the Sun at one point in the orbit and away at the other point in the orbit is what gives us those seasons.

Speaker 6 So zero order thing that happens, yes, we lose the seasons.

Speaker 4 What does this mean for the UK then? What's the weather like in the UK?

Speaker 6 The weather in the UK is sort of colder than our annual average at the moment. And in general, it's a pretty inhospitable place.

Speaker 6 I mean in the simulation I did we ended up in basically a tundra kind of climate. So

Speaker 6 it's too cold. You don't really have the seasonal warmth to get stuff growing.
The landscape we get is very different from what we would see today.

Speaker 4 What about biomes globally though? I mean, are we in a completely different planet?

Speaker 6 In the simulations I did, yes, we're in a completely different planet. So you still have your tropical band of rainforests where it's very hot and humid.

Speaker 6 And then above that, you have expanded desert zones, so much wider than we have today.

Speaker 6 And then there's a very small sort of Goldilocks zone. It's not too warm, it's not too wet, it's not too grim, where you can get the sort of forest that we would normally have today growing.

Speaker 4 And then above that, in latitude, as you go towards the poles, you very quickly quickly get into places where it's really cold it's difficult for stuff to grow and you probably start getting the expansion of ice sheets as well so we have a much bigger area that would start getting glaciated so that's interesting because I mean in some ways like that reflects what we have now where you have like deserts around the middle ice caps at the top and bottom sort of like a band of of like habitable region in between the two but I sort of would have imagined that if the earth was like upright

Speaker 4 those extremes would still be there but everything else would sort of average out a bit but you're saying that the habitable bit bit gets smaller?

Speaker 6 There's a bunch of stuff that can happen. So yes, the extremes are still there.
With a lot of these things, they're sort of a Goldilocks zone and not just in heat, but in water as well.

Speaker 6 So a little bit of heat, a little bit of water is great.

Speaker 6 If you have too much or too little of either of them, that's bad.

Speaker 6 So what you have with the seasons where the stuff shifts around is it increases the area of land where you're getting just about enough and you're not stuck at one of these extremes where it's either too dry or too hot to cope.

Speaker 4 Okay, so then what are the other factors then? So why is it that this part of the UK ends up being tundra then if the weather's just like in April?

Speaker 6 Well, so I would say it probably gets colder than that. So there's other things that feedback on the climate we have.

Speaker 6 So we have the Atlantic meridianal overturning circulation that brings a lot of sort of heat up from the tropics, up to the Atlantic and towards, and that's what warms us up and means that the UK is generally warmer than say the coast of Canada, which is the same level of latitude.

Speaker 4 Yeah, yeah.

Speaker 6 So in the simulations we did, that's one of the things that shuts down. So that's like one of the the knock-on effects of having made this big sort of change in the climate.

Speaker 6 So you get that shutting down, that makes sort of everything on our side of Western Europe a lot colder already.

Speaker 4 Okay, so suddenly we're in Canada in winter, basically, rather than the nice, like warmer, wetter climate that we have at the moment.

Speaker 6 Yeah, I looked it up. A sort of sort of coastal Iceland was sort of the analogy I was getting.

Speaker 4 Goodness me, that's very windy. That is, that's super windy.
Is there anywhere the same, by the way? If we straighten this out, is there anywhere the same?

Speaker 6 You still have this tropical band

Speaker 6 that would still be rainforests, warm, pretty humid.

Speaker 6 I think probably if we did this shift, actually you'd probably start knocking us into the sort of things we saw in like the last glacial maximum where you've got sort of big ice sheets everywhere.

Speaker 6 The whole planet starts becoming a lot drier and windier. And at that point, no, nowhere's the same.

Speaker 4 So does it get really hot at the equator and really cold at the poles?

Speaker 6 It gets really cold at the poles. It doesn't get equivalently more hot at the equator.
There's other things that limit how hot you can get in the tropics.

Speaker 4 Is it colder than it is at the moment in the poles?

Speaker 6 It's not symmetric at the moment. So say Antarctica is much colder than the North Pole is.

Speaker 4 It's because it's at the bottom, right?

Speaker 4 And the heat just wants to go. Is rising.

Speaker 6 There's all sorts of reasons. It's got a much bigger ice sheet.

Speaker 4 Okay, well I know you were talking a bit about the weather here, but we actually contacted some people at the Met Office and in particular senior reporter Aidan McGiven and what they've done for us is a weather report from Straight Axis Earth.

Speaker 4 Have a listen to this.

Speaker 7 Hello and welcome to the latest Met Office weather forecast. Following yesterday's stormy weather there is at least some sunshine around this morning.

Speaker 7 Make the most of it because it's not long before the next showers move in. All areas getting downpours through the afternoon interspersed by some brighter spells.

Speaker 7 It's not going to feel very warm though. Temperatures of 12 Celsius in the south, 9 or 10 further north.
About average for this time of year and in fact for any time of year.

Speaker 7 Westerly winds once more from the Atlantic and the Met Office have named this low Storm Simon, the 18th named storm so far this month.

Speaker 7 This is of course a fake weather report.

Speaker 7 You might be forgiven for thinking it's real because actually the weather isn't far off what we typically experience in the UK around the the middle of the autumn or the start of March.

Speaker 7 The difference is, in a world without a tilt, this is the kind of weather we'd be experiencing day in, day out, week after week throughout the year.

Speaker 7 So, it's this weather forecast for Christmas, for Easter, for the school summer holidays.

Speaker 7 So, you can forget about summer heat waves, you can forget about winter cold snaps or snow, that would become rare.

Speaker 7 Instead, we'd have everyone's least favourite weather, start of March, on repeat every month of the year.

Speaker 7 But with extra storminess, the low pressure systems affecting the UK would be perhaps deeper and more frequent than we even get in the autumn and early spring.

Speaker 7 And to understand why, we need to look elsewhere at how climates are changing across the planet.

Speaker 7 What we're talking about when you look at the difference between the tropical rainforests at the equator and these very cold climates at the poles is a bigger temperature contrast between the equator and the pole.

Speaker 7 And it's that temperature contrast that powers the jet stream at the mid-latitudes where the UK sits. The jet stream of course is this fast-flowing current of air high in the sky.

Speaker 7 It tends to pick up areas of low pressure across the Atlantic, deepen them and send them our way.

Speaker 7 And we get more of a temperature contrast across the northern hemisphere in the autumn and the winter and that's where we get a stronger jet stream and a stronger low pressure systems moving in from the west.

Speaker 7 With a world without a tilt you'd get that temperature contrast enhanced all year round so a constant stream of low pressure systems.

Speaker 7 Now it's not my kind of weather in the UK to have this all year round.

Speaker 7 I think I'd rather live near Andrew in Melbourne if he's got a spare room I wouldn't mind that because Melbourne would be just to the south of a very large desert across Australia but it would actually be reasonably pleasant most days.

Speaker 7 It would be about 20 degrees, and there would be some occasional rain, although it would be mostly dry because you'd just be to the north of that mid-latitude storm track.

Speaker 4 Right, so here's what I've heard from that. Yeah, Melbourne, lovely, doing really well, Melbourne.
Yeah, up here, basically the same as Ireland.

Speaker 4 Well, that sounds very pleasant, actually. Yeah, we've been windy and rainy for some time now.
Lots of culture, lots of culture. Do you know what?

Speaker 4 It is weird how there isn't more culture that's coming out of Ireland. We're doing fine, thank you very much.

Speaker 4 tells us, would you like that?

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Speaker 4 One place.

Speaker 4 I say let's keep the tilt. Yeah, I think that's broadly what's coming through here.
But basically almost nothing would be the same if something so fundamental about our planet changed overnight.

Speaker 4 Seasons gone, storms all the time. Temperature, you know, not great.

Speaker 4 So humans wouldn't be happy, but what about other life? Rebecca, let's start with the absence of seasons.

Speaker 4 Even without saying what the temperature would be, how would the absence of seasons affect animal life?

Speaker 9 Well, animal life flourishes enormously in the tropics which don't have seasons so depending on the temperature and the conditions that you're specifying it could be fine.

Speaker 9 Seasonality per se is not a virtue for life. It's the particular details of the temperature and rainfall and day length that vary from season to season that matter for life.

Speaker 4 What about bears? They wouldn't be able to hibernate.

Speaker 9 No that's true. A lot of animals organise their lives around the seasons and they wouldn't be able to organise their lives in that way anymore.

Speaker 4 And in the temporal world then?

Speaker 4 In places where there are seasons, how have animals adapted to it and what would the change?

Speaker 9 Obviously, they would lose the cues to start breeding. They might not get warm enough for them to start breeding because

Speaker 9 they need warm temperatures because that's when the food that they feed upon flourishes and booms, and their whole life cycle is organised around being able to use plants or insect life to sustain their growing young.

Speaker 9 And if it didn't get warm enough for the plants to emerge, or it didn't get warm enough for the insects to come out, then the animals that depend on them wouldn't be able to breed.

Speaker 4 Because, I mean, we're discussing this as if this is a thing, a switch we flip and goes out. But obviously possibly the other version of the thought experiment is this is how the planet always was.

Speaker 4 And so yes, we're always aligned, we've just evolved in a situation. How would that have changed the animals and the animal behaviour if this was always the case?

Speaker 9 So life would probably be very different because it wouldn't have adapted all these mechanisms to cope with seasonality.

Speaker 9 For example, there might be, I suspect we might see less life in the UK because so much of it depends on a higher temperature at some point in the year.

Speaker 9 So, there are species that in the northerly latitudes they sort of you know get all their reproduction done in a day or three days or something for the year and then they shut down again for the rest of the year and then their whole life cycle is timed around this you know single moment of glory when they can come out and do their thing.

Speaker 9 But for the rest of the year, they're not breeding functioning animals.

Speaker 9 And I guess that would be the same kind of closing of window of opportunity would happen for other species too if we lived in this more restricted, less benign world.

Speaker 4 How would we have evolved?

Speaker 4 What would have changed for us?

Speaker 9 Who knows? I mean, so one of the rules of life is that if you encounter harsher, more adverse conditions, you find greater levels of cooperation, either with your own.

Speaker 9 Yes, right.

Speaker 4 A model of cooperation, darling.

Speaker 4 That's all about.

Speaker 9 Yes, so you find animals working more with their own kind, but also co-opting the services of other species to get through the tough times.

Speaker 9 So banding together, working together, living together in groups is a way of all life coping with adversity as a general rule of thumb.

Speaker 9 In Australia, for example, there are groups of birds that have to breed together to have any reproductive success at all. So there's a species called white-winged chuffs.

Speaker 9 They can't breed as a pair, they don't produce any offspring. There has to be at least seven in a group to produce one chick.

Speaker 4 Polyamorous birds, yes.

Speaker 9 No, they tend to breed with each other. They help raise the offspring.
And they're so desperate to have helpers in the group that they kidnap offspring from other groups because they need them.

Speaker 9 They need workers to help raise the offspring.

Speaker 4 It takes a village to raise a child kind of situation.

Speaker 9 It takes seven or eight chuffs to raise a chick. Yeah.
So that's just because it's so tough for them to find the food that they need to cope and raise offspring that they need to work together.

Speaker 4 But this is more likely to happen. The cooperation is more likely to happen when there are harsher conditions.

Speaker 9 Yeah, so competition or limiting resources of some kind driven by environmental conditions, for example.

Speaker 4 Does that mean that you have some levels of latitude where all the animals are really selfish, and then others where they're just like much more teen players?

Speaker 9 So, as a, yes, so as a rule of thumb, if you look across all the birds, the ancestral bird is thought to have originated in the southern hemisphere and then moved north.

Speaker 9 And as you move north, you get less and less cooperation and more and more pair breeding.

Speaker 4 Really?

Speaker 9 Yeah, so we're in the selfish zone.

Speaker 4 Oh, hey, I always knew it.

Speaker 9 Relatively few cooperative breeders compared with Australia.

Speaker 4 Well, well.

Speaker 4 And dinosaurs, how would they have done?

Speaker 9 When discussing how dinosaur life might have been affected, I was most interested in thinking about whether or not they were less likely to be wiped out by a meteor.

Speaker 9 Like, so if the meteor was more likely to strike an ocean.

Speaker 4 If you tilt the Earth 22 degrees, is the Yucatan Peninsula no longer on the flight path of that particular meteor?

Speaker 9 Let's imagine it is.

Speaker 4 This is a very specific piece of the thought experiment. Okay.
So instead of hitting Mexico, it just lands in

Speaker 4 the ocean. Yeah.
Yeah.

Speaker 9 So then the catastrophe for life on Earth, I think, is probably not quite as great.

Speaker 9 It's probably still pretty bad for quite a long time, but not as horrific as it was when the meteor hit a landmass and chucked up all this dust into the air.

Speaker 4 I really want to get a globe out now and you can seal to 22 degrees and see where that would have hit.

Speaker 4 Hang on, I want to understand this then. So if it had gone in the ocean.

Speaker 4 You've done it. You've done it.
Great. Tell us.

Speaker 6 So the theory of the asteroid hitting is that it lost all this soil and aerosol stuff and you get all the cooling.

Speaker 6 But if it lands in the ocean, you get that, but you also potentially get a lot of water vapor lofted up into the stratosphere, which has the opposite effect and gets you warming. Okay.

Speaker 6 So then it becomes sort of this battle between which one wins out. Is it the warming or the cooling? Does the aerosol drop out of the atmosphere before the water gets out of the stratosphere?

Speaker 4 So you still have complete sun blackout, but now it's raining.

Speaker 6 And possibly very hot and dark.

Speaker 9 But I think the key thing is the recovery time's quicker.

Speaker 4 Right.

Speaker 9 So you're not losing plant life to such a great extent and maybe not quite as many of the dinosaurs go extinct. So you still have some loss of life but not on nearly the same colossal scale.

Speaker 4 Okay so here's what we want then. We want a button that says you can wobble the earth from like 23 degrees back to zero just as the mean

Speaker 4 strikes

Speaker 4 and then and then back back down to the seasons. Thank you very much.
We like it.

Speaker 9 I think we do want that though, do we? Because then we'd be probably be coexisting among dinosaurs.

Speaker 4 Do you know what? You make a great point. Maybe everybody has worked out.

Speaker 4 I don't think you would. If you haven't been to the cinema recently, but that's a very popular story.

Speaker 4 We are coexisting with dinosaurs. People would be very excited about that.

Speaker 9 It's brilliantly for us, though, doesn't it?

Speaker 4 A lot of the time, no. And it's a bad business investment as well, those parks.
It's never, ever done well.

Speaker 4 The insurance costs alone are ridiculous.

Speaker 4 While we're on this topic, Amori Triot is a professor of exoplanetology at the University of Birmingham. And his specialty is in discovering new planets, studying their properties.

Speaker 4 And he described the planetary factors that govern our Earth's tilt.

Speaker 10 The Moon stabilizes the axis of the Earth and it does so because as it orbits around it keeps our axis in a sort of precessing pattern.

Speaker 10 It's good because that motion effectively gives us stability like a spinning top, you know.

Speaker 10 If the moon were to be removed, there is a chance that the tides from the sun acting on the fact that the Earth is not exactly round, it's a little shorter along the pole than the equator because of rotation, and that would make progressively the action of the Sun on that and the weak but still perceptible gravity that Jupiter and Saturn produce on the Earth would cause the axis of the Earth to go through what we would call a random walk.

Speaker 10 meaning that, you know, every X thousand years the axis would just change and quite radically. Suddenly, the pole would face the sun, the north would become the south, you know, from time to time.

Speaker 10 Not from one day to the next, but over a few hundred years or thousands of years.

Speaker 10 This is likely to affect very much life on the surface because, you know, life thrives in constant conditions, but also to maybe trigger, you know, inventivity in a biological world.

Speaker 4 That's proper wobbling now.

Speaker 4 I mean, that is. Yeah, I mean, I was genuinely quite worried about that until I remember the words.
He also said, if the moon were to be removed.

Speaker 4 Well, okay. Thank goodness for the moon then.
Yeah, okay. What an experiment.

Speaker 4 What an experiment. Well, I mean, would life stand a chance on a planet like that?

Speaker 9 It sounds pretty horrific, doesn't it? I'm not so convinced it would.

Speaker 4 I mean, this is an interesting conversation itself, but there is kind of a metaphorical conversation we're having here about climate change to a certain extent.

Speaker 4 This is a way of considering what organisms would do well under a violent change, their system.

Speaker 4 The mammoth climate change we're discussing at the moment, are there organisms that just work better with that kind of change? Will evolve faster, we'll deal with it better?

Speaker 9 In theory, any organism that has a rapid generation time is going to cope better with change over a short time scale.

Speaker 9 I think in reality the pace of change that we're seeing happening now is going to be too quick for some species, but quite a lot of species will probably be able to cope with the change that we're seeing.

Speaker 9 The main way in which we see organisms coping with changed conditions on Earth at the moment is that they're kind of effectively reaching into their past, into their ancestors' experience, and plucking out something that worked for them back in history.

Speaker 9 So, there are two kind of genetic ways in which organisms can respond to a changing world.

Speaker 9 They can change the sequence of the DNA and have a brand new solution to a new world, or they can change gene expression so they can use what they've got but express it differently in response to different environmental cues.

Speaker 9 And it's the latter type of response that we're seeing mainly at the moment. And so, the range of responses that organisms are equipped with right now is based on what their ancestors experienced.

Speaker 9 If we get to dramatic change suddenly that's way different from anything that their lineage has ever experienced, ever, we're having problems.

Speaker 9 Because at that point, to come up with a new solution, we need a DNA sequence change, and that takes a long time to happen.

Speaker 9 So, the only organisms that will cope under those circumstances are organisms that breed really have a very short generation time that can rack up new mutations very rapidly in response to the changing world.

Speaker 4 Planet of the fruit flies.

Speaker 9 Well, even shorter bacteria of each flow.

Speaker 4 Oh my god, really? Yeah. When we were talking about

Speaker 4 this model that you made, what about things like greenhouse gases? What happened there?

Speaker 6 So we didn't have a functioning carbon cycle in the model. But this 23 degrees that we have now is not a constant.
It's not always that.

Speaker 6 It wobbles back and forwards at the moment with about 40,000 years sort of periodicity between about 21 and 24.

Speaker 4 So it's only

Speaker 6 two degrees. Yeah, yeah, yeah.

Speaker 6 So there's various things about our orbit that change very slightly about how circular or elliptical it is around the Sun, the wobble, a few other bits and pieces that make these very small changes to how much solar radiation you get at different latitudes.

Speaker 6 But, I mean, if you look back in climate, we have ice age cycles. We have hothouse worlds, we have snowballed earth worlds.

Speaker 6 There's all sorts of things going on, but particularly these ice age cycles over the last few million years.

Speaker 6 It's not just the solar insulation that's making this happen, but the solar insulation is triggering feedbacks with the carbon cycle that changes the amount of greenhouse gases in the atmosphere.

Speaker 6 And it all sort of leads to these big changes that run away into suddenly having suddenly over 100,000 years ice sheets over the whole of North America that then fade away again.

Speaker 6 So that's just with a couple of degrees of axial tilt rather than taking away all 23.

Speaker 4 I do wonder as the climate changes,

Speaker 4 is there any risk that we could change the axial tilt itself by our actions?

Speaker 6 So that's happening to a very tiny degree. A lot of this stuff depends on exactly where the mass is on Earth.

Speaker 6 Because we have such precise measurements from satellites of where we are in space relative to the fixed stars and how we're moving,

Speaker 6 you can detect in that very small changes because of either massive extraction of groundwater or we're starting to see that from the melting of ice sheets as well, because that's moving water around the planet.

Speaker 6 So, to an absolutely minuscule, tiny degree, yes, we can see that in sort of changes in the orbital powers of the Earth, but the effect of that is absolutely dwarfed by the greenhouse gases that we're just pumping into the atmosphere.

Speaker 4 These models that you make to do silly, crazy things like switch off the tilt of the earth, normally you actually put these models to sort of more sensible use, right? Yes.

Speaker 6 I might contest whether that was a silly thing to do in the first place. So there are two main things we do with these classes of models.

Speaker 6 One is we run them in different ways just to understand how these different components and processes feed back with each other, because it's such a complicated network of feedbacks, it's really difficult to just sit back and work that out from first principles in your head.

Speaker 6 You really need to have a system that has all these things going and you can see how they express themselves.

Speaker 6 So there's an element there that's just basic understanding of the climate system and these kind of silly experiments are ways ways of seeing how those things change and work together.

Speaker 6 The other one, of course, is making projections of climate change and what we think the world will be like once we have however many ppm extra of greenhouse gases in the atmosphere.

Speaker 4 And I guess the final, most important question of all is, are we all in agreement now that theatre only exists because of winter? Is that where we're at? I think we're fine with that.

Speaker 4 Okay, yeah, sure.

Speaker 4 And for my next play, should I focus on which is more difficult to achieve to re-tilt the earth or remove the moon? These are the two.

Speaker 4 Thank you to all of our guests, Aiden McGivern, Armorie Triot, Rebecca Kilner, and Robin Smith.

Speaker 4 It's not good, is it? No. Or, other way to think about it, what we've got now is good.
Yeah, that's, you know, that's the positive message from this. Like, it's one of those little kind of cosmic...

Speaker 4 chances that we happen to be tilted at this angle because of some bump that the planet got a long long time ago and it's worked out in our favor thank goodness for that aren't we lucky oh we are you know enjoy that winter but if you look up one day and the moon's gone

Speaker 4 sorry about that

Speaker 4 subscribe to curious cases on bbc sounds and make sure you've got push notifications turned on and we'll let you know as soon as new episodes are available I'm Rory Stewart and I want to talk about heroes.

Speaker 11 When I was a child, I imagined a heroic future for myself in which I would achieve great things and die, sacrificing my life for a noble cause before I was 30.

Speaker 11 But my experiences in the Middle East and in politics showed me that there was something deeply wrong with my idea of heroism.

Speaker 11 From BBC Radio 4, my podcast, The Long History of Heroism, explores ideas of what it meant to be a hero through time. How have these ideas changed? Who are the heroes we need today?

Speaker 11 Listen to Rory Stewart, The Long History of Heroism, first on BBC Sounds.

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