What triggers ice ages and other climate events? How are sunspot cycles and orbital motions related to climate patterns? What does Jupiter have to do with all this? I discuss these questions and more in today’s Ask a Spaceman!

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EPISODE TRANSCRIPT (AUTO-GENERATED)

In the year 1645, the sun shut off. Not literally, of course, it was still shining, still rose in the east every morning, set in the west every evening, still shone bright and strong, but something was wrong. It would stay wrong for over half a century. The problem was with the sunspots or rather the lack thereof. This period coincided with the lowest number of recorded sunspots ever for decades before and for centuries since.

We had just gotten the whole rigorous and systematic measurement of sunspot activity for no particular reason game started, you know, really started with Galileo. Humanity has known about sunspots forever. You can see them, if the sun is very low in the horizon and partially obscured by fog or mist or thin clouds. And if you squint hard enough, you can see sunspots. People have known about sunspots, but it wasn't until the telescope and the ability to point the telescope at the sun and then project the image of the sun on a screen could you really get serious about sunspots.

And Galileo really did observe sunspots a lot. And then after him, people did, a lot. People liked sunspots. And so at the time that this occurred, this dip in sunspot activity, nobody knew anything was special or different because they had just started measuring and counting sunspots and didn't have anything to compare it to. It took a few more centuries for us to be able to look back at the time and realize that something was wrong.

The first person to notice that something was wrong was german astronomer Gustav Spohr who, if you need to visualize him in your head, he had one of these fantastic chinstrap style beards. It's just it's just magnificent. But that's unrelated to his research on sunspots. In 18/87, he did that. And then there was further elaborated by the husband and wife team of Edward and Annie Monder.

But it wasn't until 1976 that we finally got a name for what went down all the way back during the late 1600 and that name has stuck around as the Monder minimum. I suppose the alternative was the spore slumber, so I'll allow it. The Maunder Minimum was wild, really wild. We're we're used to sunspots just being there. Yes.

There's roughly, an 11 year cycle where some years there are fewer sunspots and some years there are more, But seriously, go look at the sun. Note not with your eyeballs. It's somewhat dangerous and by somewhat, I mean extremely. But if you look with even a decent telescope, you're likely to see at least a couple spots. If you want to use a more powerful telescope, you can just look up NASA's Solar Dynamics Observatory, which gives nearly real time updates on the surface of the sun.

As I and as I'm preparing my notes right now, I see 1, 2, 3, 4, 5, a handful. Let's go with a solid handful of sunspots. This was not the case during the maunder minimum. To give you some perspective, during a typical, say, 22 year period, consisting sunspot cycles, we're likely to count between 30000 individual sunspots. During the Maunder Minimum, there was a period of time right at the end of the 1600 when there were 0.

0. There was a 22 year period right there where there were 0 counted sunspots. And that's not for lack of trying. Sure. We had we have no idea how many sunspots there were during the year 2 10 or the year 13 50.

But in the late 1600, there were people like Giovanni Cassini over at the Paris Observatory who were making meticulous observations and recordings. And that was not the only outfit doing the same thing, so we can cross check and validate all of these independent measurements. And we have to give a huge hat tip to those astronomers in the late 1600, early 1700 because at the time, they were just making the measurement for the sake of measurement. They didn't know why it was important. They didn't even know what sunspots were, or how they worked, or what caused them.

It was just some phenomenon that appeared in nature. And so thank you astronomers because it's your efforts in the pursuit of pointless scientific measurement that allow us, centuries later, to finally understand what was going on. There were entire decades going by here during the Maunder Minimum with no observed sunspot 0 observed sunspots. And during the Maunder Minimum, there were 3 total solar eclipses. There's 1 in 1652, 1 in 17 06, 1 in 17 15.

And from eyewitness accounts and a few hand drawn sketches, the solar corona, the atmosphere of the Sun that's visible during a total eclipse, was abnormally small and weak and and kind of lumpy. It was unstructured. Something was wrong with the Sun. By the 2nd decade of the 1700s the sun apparently got its act together and ramped back up to its normal sunspot levels where it stayed roughly in these centuries ever since. There are still ups and downs, of course, but nothing nearly approaching the Monder minimum.

Now if this episode was just about the Monder minimum, it would be rather short because at this stage in the podcast I move into a fun little discussion about what caused the Maunder Minimum and the cool physics behind it. But the thing is, we don't know what happened. We don't. We know for sure that the Maunder Minimum happened, that there was a nearly 3 quarters of a century period where the sun had essentially no sunspots. And before that, it was pretty normal.

And after that, it was pretty normal. And in the century since, we've seen the 11 year sunspots cycle, we've seen some longer cycles, maybe century long cycles beginning to take shape, but the Maunder Minimum has not happened since. It may have happened before. It almost certainly happened before, but no one was around to observe it. And despite all of our knowledge of what causes sunspots, magnetic fields, we don't know why the sunspots shut off during the maunder minima.

We just don't. It's a mystery. Go ahead. Write a paper on it. Submit it to the astrophysical journal.

If you've got a good idea, go for it. It's just as good as all the other guesses. So we don't know what caused the Maunder Minimum, but we do know about something that happened on the earth right around the same time frame, something known as the little ice age. This term was first introduced in the early 20th century, and like most concepts introduced in the early 20th century, it has a rather loosey goosey definition. Roughly, very roughly, the little ice age is a period of measurably colder temperatures throughout the North Atlantic spanning from the 16th to 19th centuries.

And it was noticeably colder. You know, we don't have very detailed or accurate temperature measurements of the time. You know, it's not like we have in the 16th 17th centuries, we have global satellites, you know, getting surface air, water, temperatures across the globe, constantly monitored. No. We didn't have that technology.

Not a lot of people were taking accurate measurements at the time or regular measurements at the time. But from the records that we do have and from the historical accounts of what people were experiencing, like, here's another year with no summer. Here's another year where the it's it's snowing in May. Here's another year where the harvest failed again. There is ample evidence during this time that at least the North Atlantic region is especially Europe was hard hit by colder than average temperatures.

To be clear, as far as we can tell, this was not a global cooling event. We have other cultures and societies who are making temperature measurements. We have their records of their harvest. We know how well they were doing, and they don't seem to be as hard hit. This seems to be focused on the northern Atlantic, particularly Europe, but it was also very real.

And if you were a peasant struggling through the shorter summers and brutal winters of the period, you didn't really care if it was a global event or not. Within this overall cooling of the North Atlantic region called the little ice age, there were several bursts of intense extra chilliness with one starting right around 1650. 1650. 1650. What was happening in 1650?

Oh, right. The spores I mean the Maunder Minimum. Now this this is a coincidence. We have an intense burst of cold during the the little ice age. We have an extra burst of coolness happening right around the same time when the sun is producing fewer sunspots.

Now a coincidence doesn't make for great science, but we know that the sun is largely responsible for keeping the earth warm, and we know for a fact that changes in the amount of sunlight drastically affect the earth's weather, like, the contrast between day and night or the contrast between the equator and the poles. How much sunlight you get really does determine your average temperature. But now we're using these basic facts that the amount of sunlight hitting any patch of the Earth is important, and this strange coincidence between the Maunder Minimum and the little ice age to draw a larger conclusion that changes in the properties of the Sun are also connected to the Earth's climate. You know, we're used to weather patterns and and the weather at northern latitudes is cooler than the weather at the equator, but now we're talking about the climate. We're talking about large systems, global systems, or vast hemispherical systems of great massive slow temperature changes that affect entire regions of the globe, if not the entire globe itself.

This is an interesting question. Do changes in the sun's output affect the entire globe, and is the Maunder Minimum evidence for that connection, the fact that it overlaps with the little ice age? Now I have to preface the following discussion about this strange coincidence that the modern consensus on the connection between the little ice age and the Maunder Minimum is a strong and resounding and a very deliberate shrug of the shoulders. Here's what we have. On one hand, you have the fact of the little ice age and maunder minimum overlapping, which is like a big flashing neon sign that these may be connected.

There aren't exactly a lot of little ice ages in recorded history, and there's nothing like the maunder minimum in recorded history. And, sure, we're only working with, like, 500 years of solid data, but in that 500 years, these two events just happen to line up. But on the other hand, you have the fact that the little ice age started before and ended after the Monder minimum, and that the maunder minimum affected the whole entire sun. It wasn't just like part of the sun was losing sunspots. The whole entire sun was losing sunspots.

And so if you're going to change the whole entire sun, presumably, you would change the whole entire earth, and so you have to ask why we have a little ice age in Europe and not a big ice age in the whole entire earth. But on the third hand, this isn't as crazy as it might seem. For one, we know through modern measurements that sunspot activity is correlated with solar output. During periods of time with fewer sunspots, the sun is overall a bit dimmer, not by much. We're talking less than 0.1% or something like that, but that's not nothing.

And let's be honest, the climate system of the Earth can be just a little bit sensitive to even tiny changes in the wrong direction, like mild increases in carbon output. We get this through forcings and feedback mechanisms. You heat up a little bit of the Earth that changes the Earth's climate in a little way that makes it more receptive to that additional heat, which warms the earth more, which makes it even more receptive, and you can trigger feedback cycles. So even tiny changes in the sun's output can have big effects. And second, why this night might not be as crazy as it sounds is that the North Atlantic region of the globe is kind of different, and it might feel some effects of different solar intensities before the rest of the planet does or in a way that the rest of the planet doesn't.

For example, we have this whole axial tilt thing. The northern hemisphere spends half the year pointed away from the sun and the other half of the year pointed towards the sun. And so if you're going to change solar output, if you're going to heat up the sun or cool off the sun, that's going to change your entire seasonal pattern. If you heat up the sun a little bit, in the equator, you go from hot to slightly hotter. That's not big of a change.

But in the northern hemisphere and also the southern hemisphere, if you heat up the sun a little bit, all of a sudden your summers are longer and your winters are shorter, which can have its own feedback mechanisms. You're gonna notice that more than you would at the equator. In the northern hemisphere, the northern latitudes are different than the southern latitudes because I don't know if you've noticed, but if you head down to the southern latitudes, it's mostly ocean. And water takes forever to heat up and slow down. If you've ever tried to boil a pot of water to cook some pasta because you're starving, it takes forever.

Imagine doing that to an entire ocean, but northern latitudes are mostly land. In fact, most of the Earth's land mass is concentrated in the northern latitudes of the globe, and land can change temperature far faster than water. So if you're gonna change the output of the sun, the northern latitudes are going to feel it differently. So the northern hemisphere is potentially much more sensitive to changes in solar output than any other region of the globe, which means, like I stated at the top, the little ice age monitor minimum connection isn't as crazy as it sounds. But it is ultimately just a coincidence and so we land at our in the conclusion on whether the monitor minimum is responsible for the little ice age, but whatever the status of the little ice age and its connection to solar output let's zoom out a bit.

The little ice age, even though it was a big deal for the peasants of Europe, I mean, it wasn't all bad. There were these awesome things called frost fairs when the river Thames would freeze over, and that sounds like fun. We don't get those anymore. Whatever the little ice age was, it was not a long term shift in climate. It didn't affect the whole globe, and it only lasted a few centuries at most.

And a few centuries is a long time for humans, but for the Earth, it's like nothing. For that, you need Patreon. That's patreon.com/pmsutter to give you the truly geologic perspective. And I truly am humbled by all of your contributions. Every single dollar goes to support the show and keep the show going, and I truly do appreciate it.

That's patreon.com/pmsutter. So we wanna zoom out. The little ice age and the maunder minimum overlap in time a little bit, but the little ice age started before and ended after. Maybe there was something funky going on with the sun. Maybe it was starting to cool off before the sunspots disappeared and then lingered even after the sunspots returned.

We don't know. We don't have access to those observations, those measurements. But let's leave that coincidence where it is, unresolved and full of interesting little tidbits about the nature of the relationship between the sun and the Earth's climate. And let's zoom out. Let's look at real geologic time.

Who cares about all this centuries long cooling in the North Atlantic? That's peanuts. Let's play with the whole planet. We know that with the exception of the Maunder Minimum, the sun's output doesn't change dramatically over scales of decades or even centuries. It really doesn't.

And, yeah, over the course of the 11 year sunspot cycle, the sun's output will change a little bit, but it's barely anything. Like, we can measure it because we're good at measuring things like this, but it it's not huge. And also these changes in the Sun's output over the 11 year sunspot cycle obviously don't impact the Earth's climate because, in case you hadn't noticed, the Earth's climate doesn't drastically change back and forth every 11 years. There's no connection there. But what about longer time spans?

What if we go back tens of thousands of years, 100 of thousands of years? Are there any patterns we can tease out? Any shifts in the Earth's climate that we can connect to the sun? And oh yeah, we can. But it's not because of the Sun itself.

This connection between the Sun's output in the Earth's climate has nothing to do with, well, the Sun's output. We're lucky. We have a remarkably stable star that, yes, as it ages, it gradually warms and in about 500000000 years will boil our oceans, but that's that's somebody else's problem. Occasionally, it throws a temper tantrum. Occasionally, it has a maunder minimum or or a giant solar flare, whatever.

But largely, it keeps the same brightness day in and well, also day in because when you're the sun, you're always on the clock. But the Earth's relationship to the Sun does change and it changes because of our orbit. Our distance from the Sun changes with time. The structure of our orbit and the position of our planet and the orientation of our planet changes with time. And this changes in a much bigger way than the sun's own output.

This changes how much sunlight we get on the earth. And thanks to the magic of Newtonian physics, these changes follow a series of regular and predictable patterns. Because it's all just gravity. And once you figure out the math of gravity, you can figure out the dance going back billions of years and going forward billions of years. You just run the the clock forward on all your math.

That's it. The first person to propose this connection was a Serbian physicist and astronomer Militin Milankovic in the 19 twenties. So as is usual, we name these patterns the Milankovic cycles, and there are several of them. The first cycle is that our orbit, the orbit of the earth around the sun slowly changes shape. We have a slightly elliptical orbit.

We have a measure of the ellipticity of the orbit, of how stretched out our orbit is. We call this number the eccentricity. Currently, it is 0.0167. And if you need some context for that number, that means we are slightly mildly elliptical, but not perfectly circular in our orbit. But this changes with time.

You know, imagine the the orbit being this like hula hoop around the sun. This loop around the sun and you can squeeze it one way and then squeeze it the other way and then squeeze it back and squeeze it back and so it will oscillate. It will vibrate. It will change from being elliptical in one direction, and then getting stretched out till it's perfectly circular, and then getting stretched out in the perpendicular direction, and then back and forth, back and forth. This cycle takes about a 100000 years to complete.

These cycles are dominated, are driven by gravitational interactions with Jupiter and Saturn, and are actually the combination of many many different gravitational forcings, little tweaks and nudges to our orbit due to the gravity of those giant planets operating over the course of 1,000, tens of 1,000 of years. Our ellipse changes from a maximum of 0.02 to a minimum of negative 0.03. That just means the ellipse points in the perpendicular direction. Like I said, it's currently 0.0167 and it's on the way down. We are steadily getting more circular with time.

And what this does is it changes the lengths of the seasons. Because the earth, as it travels on the ellipse, when the earth is at its furthest point from the sun, at the at the tall and the far end of the ellipse, it will spend a lot of time there. We move slower. And then when the Earth is on the short side of the ellipse, on the squeezy part of the ellipse, we move faster. This is basic Keplerian physics, good old Keplerian motion.

How does this impact the length of the seasons? Well, imagine your summer in the northern hemisphere happens to line up with the outermost part of the ellipse, the part that's far away from the sun. Now on one hand, you might think this is gonna be a negative because you're a little bit more distant from the sun, But the bigger effect is that you spend longer the planet spends a longer in that part of the ellipse than on the short side. So when your northern hemisphere summer and you're pointed towards the sun, you're going to spend a longer pointed towards the sun than when you're not. This has a potential impact on climate.

This impacts the temperature over the entire globe, of course, but it especially impacts the temperatures experienced in the northern and southern latitudes. And like I said before, the northern latitudes especially are more sensitive to changes in the amount of sun that they get because of the axial tilt already, because the amount of land area. There are other things, the the amount of forest that that wax and wane between full of leaves and not full of leaves that changes the reflectivity of the Northern hemisphere. And there's, ocean currents that, you know, there's all sorts of stuff happening in the Northern hemisphere that the Southern hemisphere simply lacks. The Northern hemisphere is very sensitive to these changes.

The second cycle has to do with our axial tilt. The technical jargon term here is obliquity. Every 41000 years, we cycle between an axial tilt of 22.1 degrees and 24.5 degrees. Currently, our tilt is 23.44 degrees, and it is decreasing. As you might imagine, the more you tilt the Earth, you are going to impact the magnitude of the seasons.

If the earth is more tilty, then the summers are gonna be more intense because you're getting blasted by the sun, and the winters will be more intense in the opposite direction because you're just stuck in shadows all the time. And then if the tilt is very mild, then the seasons will be more evened out. So that's another cycle operating every 41000 years. There's a third cycle called axial precession. The earth isn't just spinning on its axis.

The axis itself is wobbling like we're a giant spinning top. If you go to the North pole and look straight up, draw a line from the north pole of the earth out into the sky. You'll intersect near the star Polaris, hence the name Polaris, but this isn't always the case. This actually the north pole actually draws out a circle in the sky. It takes about 25,700 years to draw out that circle.

This axial precession, this 3rd cycle with the period of 25,700 years changes which hemisphere gets more sun. Right now, the time when the earth is closest to the sun in our ellipse, when we're on that short side of the ellipse and we're nice and tight and nice close to the sun, lines up with southern hemisphere summers. So so you get a double whammy down in the south, but the south don't care because it's mostly ocean. In 10000 years, it will be the reverse where northern hemispheres will be closer to the sun during their summers, and that has a much bigger impact in climate than the southern bits. There are other cycles like the fact that the ellipse of our orbit slowly rotates around the sun and that the angle of our orbit slowly changes, but what this amounts to is that you have multiple overlapping cycles that each have their own impact on the earth and specifically each has their own impact on the northern latitudes, which are very sensitive to this kind of stuff.

You have our orbit changing from a circle to an ellipse. You have the Earth's tilt changing, and you have the Earth's tilt rotating around. Sometimes these effects reinforce each other. Sometimes they cancel each other out. Sometimes there'll be a period of time where one of these effects dominates for tens of 1000 of years, and the earth is most sensitive to that particular part of the cycle.

And then there are other times where where like say the axial tilt is more important or the precession is more important. And again, I can't emphasize this enough. There's the effect you have on the whole entire globe, and then especially the effect you have at Northern latitudes. Now how does this change our climate? Well, it's actually fascinatingly more complicated than you might think.

Like, it's easy to think. Yeah. If you're closer to the sun, it's gonna get hotter. And if you're farther from the sun, it's gonna be colder. Yeah.

Obvious. But there are other things like the fact that the amount of UV radiation hitting our upper atmosphere changes our ozone layer, changes the temperature of the outer layers of our atmosphere, which changes how heat is transported throughout the Earth and how much radiation escapes. So it's not just direct raw sunlight. The amount of UV radiation specifically has an effect on climate. And there are other things, wild things that you would never think of in a 1000000 years, like cosmic rays.

When the sun is brighter or when we are closer to the sun, we are more well protected from cosmic rays streaming in from interstellar space. And what do cosmic rays do? Well, they seed the formation of clouds. Yeah. Yeah.

I'm I'm not kidding. They they like hit molecules in the atmosphere and ionize them. And then that starts the process that starts clumping water molecules together. And so you can start forming clouds. If you have fewer cosmic rays hitting the earth, you can't form as many clouds.

And if you have more cosmic rays hitting the earth, you have more clouds in that the more clouds you have, the more reflective our atmosphere is, which actually, ironically, cools you off. So the closer you get to the sun, the more well protected you are from cosmic rays. The more clouds you have, the more reflective you have. The more reflective you are, and the cooler you get. And so there are all these intricate forcings and mechanisms, like sunlight.

You get more sunlight, you get more trees, and then more trees happen in the northern hemisphere. They get more leaves, but then the leaves are really good at absorbing sunlight, and you have to work through the consequences of all these little interactions, and it's a really fun game. But you can add up the effects of all these cycles and the impacts that they will have through direct temperature forcing, through UV radiation, through cosmic rays, and you can map out how much sunlight the earth as a whole is getting. You can map out how much sunlight any particular latitude is getting, and you can do this over the course of 100 of 1000 of years, even 1000000 of years, thanks to the magic of Newton's math. Now I do have to say these effects are small.

Across the whole entire earth, it's less than a percent change in the amount of sunlight you're gonna get, but it's bigger at higher latitudes, especially in northern latitudes where these effects are going to be amplified. So here's what we have. We have a plausible mechanism of changing the climate of the Earth through the nature of our orbit. We have ways that we can measure and predict how that change in sunlight is going to impact the earth's temperature. We can model all that using our knowledge of of physics and biology and geology.

And so if you're a fan of this idea, your job is to go looking at the Earth's temperature history using some handy proxy like ice cores, and I would love to dig into that someday. So someone please ask how we measure ancient temperatures on the earth and see if there's a match. We can measure temperatures going back tens of thousands, 100 of thousands of years, and we can know exactly what the Milankovitch cycles are up to at any time of day, any year, and we can see if anything lines up, and there's a match. When we're getting more heat from the sun, especially in northern latitudes, we tend to have higher temperatures on the earth. And when we're getting less heat from the sun, well, as you can imagine, it's a little bit colder as in ice age colder.

But I'm not talking about little ice age. I'm talking about the real deals, Glaciers, wooly mammoths, saber tooth tigers, and everything. That's right. If you've ever wondered what causes ice ages in geologic history, this is it. It is the shape of our orbit in the orientation of our planet.

It is the relationship between us and the sun, and that is pretty mind blowing. Ice ages. And note, if you ever are reading about ice ages, there are 2 different kinds of ice ages that geologists use. 1 is a definition where any time that the earth has polar ice caps of any kind, you are in a quote ice age. And so according to that definition, we've been in an ice age for 2 and a half 1000000 years.

There was a period of time before that when there were no polar ice caps at all on the earth or very, very small ones. But colloquially, when we say ice age, and we think woolly mammoths and saber saber tooth tigers, and, you know, ice sheets covering Canada and parts of the United States and, like, half of Europe and all that, We're talking what geologists call glacial periods. So periods where there were extra ice caps. And when you measure these, when you line up all these bits of information, the Milankovitch cycles telling us how much radiation the northern hemisphere of the Earth is getting. When you look at ice core samples and you look at temperature variations over the past few 100000 years, and when you look at geologic records for when glaciers were advancing and at their maximum extent and then retreating and then going back out again, they all line up.

And this is think about the end of the last ice age, about 12000 years ago, when the glaciers last retreated. Think of all the changes that had all the effects it had on humanity. Once the glaciers retreated in North America, people were able to populate. Humanity was able to move south into the continental parts of North America, and down into South America. Big game species that humanity had hunted for for, like, forever disappeared.

Huge changes, and it was all brought about by a tiny, tiny change in our orbital configuration. Our orbit shifted slightly and had and had huge impacts for humanity. If that's not a cosmic influence on humanity, then I don't know what is. Thank you to Golly f on YouTube for the question that led to today's episode, and thank you to all of my Patreon supporters. That's patreon.com/pmsutter where you can go to support the show.

I'd especially like to thank my top contributors this month. We've got Justin g, Chris l, Barbike, Duncan m, Corey d, Justin z, Nalia, Scott m, Rob h, Justin Lewis m, John w, Alexis, Gilbert m, Joshua, John s, Thomas d, Simon g, Aaron j, and Valerie h. It is all of your support that I count on every single month to keep this show going, and I can't thank you enough. And I can't thank you enough for all the reviews on Itunes, on Spotify, on all your favorite podcasting platforms. That really helps gives the show visibility.

And I can't thank you enough for all the questions. Keep them coming. The best way to send me questions is through email, ask a spaceman@gmail.com, or go right to the website, askaspaceman.com. And I will see you next time for more complete knowledge of time and space.

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