Astrum Space - What Milankovitch Cycles Will Do To Earth

Episode Date: November 13, 2023

In today's episode, Winter is coming. But not all winters are created equal. Join with me as we learn about Milankovitch cycles; the millennia-long changes in the Earth’s motions that slowly but surely bounce our climate between pleasant warmth and freezing ice-ages... with the next one on the way.

Winter is coming, said Edd Stark. When he uttered his famous words in the TV series of Game of Thrones, it was more than just a pronouncement of the normal passing of the seasons. Rather than lasting a mere four months, winter in the fantasy realm of Westeros could be a big problem. It could potentially last for years, even up to a decade. Crops would be harder to grow, the weather would be colder. The arrival of winter was the harbinger of an era of hardship.

Of course, while Westeros is pure fantasy, seasons that last for years on end are not limited to fictional stories. We experience them on Earth. Various cycles are playing out on our planet, and when they are in conflict, we experience a period of stability. It's worth noting, though, that they will not be in conflict forever. In our future, winter is coming too. What are these cycles? How can better understanding them help us prepare for our future?

I'm Alex McColgan and you're listening to the Astrum podcast. I started this podcast by describing seasons that lasted years. Join me today in exploring the different cycles that affect our planet's weather and warmth. To begin, we should probably ask a simple question. What causes the seasons that we are familiar with? You may well already know the answer. to this question, but as it will provide the starting point for what comes later, it's worth reviewing. Besides, this question is not entirely straightforward, depending on where you are on the planet, you may not actually get any seasons. Generally speaking, seasons we know of are caused as a result of our planet's tilt. Because our planet rotates at a tilted angle

as it orbits the sun, one hemisphere will point towards the sun during part of the year, while the other will point away. Naturally, hemispheres that are pointed towards the sun become much warmer, while pointing away from the sun makes them colder, creating the regular seasons, summer and winter. This effect becomes stronger the higher up or lower down the planet you go. Consider the small Norwegian town of Tromsse. Because of its higher altitude, Tromsa isn't just pointed more towards the sun. The tilt of the Earth is such that, from its perspective, the sun The sun never sets for months in summer, and never rises for a few months in winter. Naturally, this produces quite the seasonal variance.

But this effect lessens the closer to the equator you get. There, the tilt of the Earth doesn't really change how close or far away from the sun the area is, and as such the Earth doesn't notice much temperature variation. It's all just a question of how close you are to the Sun. However, did you know that the tilt of the Earth isn't static? Nor is it the only thing about the planet's orbit that influences how warm or cold we are. Imagine for a second the model you are familiar with, of the Earth orbiting the Sun in a nice circle flat to the plane of the Solar System.

In this model, we circle the Sun because of the Sun's gravity. This model is too basic. In reality, the Sun is not the only source of gravity pulling at us, although it is the biggest. Many of the planets pull and tug at us, particularly large ones like Jupiter, which has a mass 318 times the size of our own planet, or Saturn, which is 95 times, and we in turn pull on them. As planets all rotate at different speeds around the Sun, this constant pulling and releasing creates a delicate dance, far more complicated than a simple circle. This interplay of increasing and lessening gravity has many different effects on our angle of

tilt, our orbit, and even the plane in which they occur. Broadly speaking, these variables have stabilized into cycles. These cycles were first described effectively by Serbian geophysic and astronomer Melutin Milankovic in 1920, and thus were called Melankovitch cycles. The first such cycle I want to look at is the changing shape. shape of our orbit. Over the course of a 100,000 year period, the Earth's orbit around the Sun becomes more and then less elliptical.

Naturally, if our orbit is closer to that of a circle, our distance from the Sun remains relatively consistent, and we get about the same amount of sunlight all year round. However, once our orbit becomes elliptical, there are parts of the year where we are further from the Sun and thus colder, and parts where we're closer and we're more. warmer. As it happens, the perihelion of the Earth's orbit, or the bit where we're closest to the Sun, happens roughly on January 3rd, while the Apheelian, or the bit where we're furthest away, happens on roughly July 4th. I'm recording this in the UK, which means for my hemisphere, January is winter. So for me,

this is quite nice. Although we are in a phase right now where this cycle of the Earth's orbit is more circular than it is elliptical, we still experience a 7% difference in the amount of sunlight we receive in January compared to July. This sunlight difference means that my northern hemisphere's winters are warmer, while our summers are milder. In the southern hemisphere, the reverse is true. Because they're experiencing summer during this warmer phase, their summers become even warmer, become colder. And that's just at this stage of the 100,000-year Milankovic cycle. As the Earth's orbit

becomes more elliptical, that 7% sunlight difference turns into a 23% difference, quite significant. You might think this seems overall a little unfair on the Southern Hemisphere. The Northern Hemisphere benefits from this cycle stabilizing its seasons, while this cycle makes the Southern hemisphere seasons more extreme. Don't worry though, as another cycle is at play to bring things full circle. This current seasonal rotation happens because the Earth's tilt is consistent as it orbits. Except it isn't consistent. Little by little, the angle the Earth's axis is rotating along is changing too. It moves as if it were drawing a circle on the sky above it, in a cycle the last 26,000 years.

One upshot of this is that while our axis is currently pointing at the North Star, or Polaris, this will eventually no longer be the case. Over time, it will point at different stars, before eventually circling back to point to Polaris again. The other upshot of this is that in 13,000 years, the Northern Hemisphere will be having its summer in January, while the Southern Hemisphere will be the one with a white Christmas. So, then it will be us experiencing a more profound seasonal variation. While harsher winters are unpleasant, they are not what I promised.

I started this video by describing seasons that lasted years. These exist too. There are Melankovic cycles that create winters that last for thousands of years. Or to speak more accurately, there are Melankovic cycles that help cause ice ages. We don't fully understand how ice ages come and go. There are numerous theories. However, it must be noted that some of the 100,000 years spans of ice ages line up extremely well with the 100,000 year Melanchovich cycles.

For instance, there is a cycle whereby the plane on which the Earth rotates around the sun rises and falls over the course of 100,000 years. This change in its orbital inclination does not obviously explain. why it is that the Earth would be getting colder or warmer? After all, the Earth is still the same distance from the Sun. However, it lines up so perfectly with the time periods ice ages were occurring at over the last 800,000 years that scientists conclude that there must be a connection. Perhaps cosmic dust lying in the plane of Earth's orbit blocks out some sunlight when we are at one inclination, but is not in the way when we are at another.

could go some way toward explaining the occurrence of ice ages during these time periods. Whatever the case, there is at least one other cycle that influences the arrival of ice ages on Earth, and this might perhaps be the most important for us today. It is the tilt of Earth's rotation. I already mentioned that this axis of tilt rotates around the planet, but it also changes the angle at which it does this. Over the course of 41,000 years, it has been a little bit of 41, it alternates between 21.1 degrees and 24.5 degrees. At the moment, it is 23.4 degrees and is declining. You might think that this is a good thing. The smaller the angle of tilt, the less extreme our seasonal temperature variations might be, and the warmer our winters will become. Surely that

is a good thing for avoiding ice ages. Surprisingly, it is quite the opposite. Left to its own devices, This lessening tilt would lead us into another spreading of the ice sheets and cooling of the planet that would hit its peak in 9,800 years. It is not the harshness of the winter that causes this spread, but strangely enough, it is the mildness of the summers. You see, when winters occur, snow builds up at the top of mountains and in cold polar regions. In warm summers, this snow tends to melt away. However, if the summer is mild enough, the snow sticks around, becoming a more permanent feature

of the landscape. Icey snow is white in colour and reflective, which means that light has a tendency to bounce off it rather than be absorbed by it. This means that if the earth is covered with ice, it reflects sunlight back into space and actively becomes even colder, thus creating conditions for even more ice. In more than one sense of the word, this is a snowball effect. effect. We are right now in an interglacial period.

This is a brief moment of warmth that lasts a few tens of thousands of years or so in dispersing a deeper, more general cold trend. If it wasn't for this warmer uptick, we would actually be in an ice age right now, and from a technical perspective, actually are in an ice age, just one we're not fully noticing. If it wasn't for this briefly warm interglacial period, mankind would have experienced ice across the history of its entire existence. Thanks to the Melankovic cycles, that brief period of warmth will someday end, then winter will truly come. Of course, this is under the assumption that Melanchovich cycles are the only factors that influence global temperatures.

And while broad trends lasting 100,000 years and interspersing upticks every 41,000 years are indeed demonstrable and consistent in parts of fossil record, the location and orientation of our planet are not the only thing that matters. CO2 and methane levels in the atmosphere are also driving forces behind global temperature fluctuations. And if we're not careful, just as an ice age can build up with a snowball effect, stripping away of ice can happen in the same way, but in reverse. Less ice means less reflection of sunlight, making things overall warmer, which leads to less less ice. Still, if Melankovic cycles are the only factor in action, we are in for a

cold future. The Melankovic cycles affecting the planet currently are mostly working to stabilize the system, leaving us in a temperate, relatively even temperature zone. However, there will come a time when they will make temperatures, hot and cold, more extreme. We would do well to keep these cycles in mind. Melankovic cycles are in it for the long haul. Winter might not be coming for a long time, but one day our planet will face winter again. Well, that's all we have time for today. I hope you've enjoyed listening to this podcast on Milankovic Cycles. If you like what you've heard, please feel free to follow us for more podcasts on other fascinating space topics.

But for now, I'm Alex McCalligan, and this has been Astrom. All the best, and see you next time. You're great at protecting your data, but lots of places could still expose you to identity theft. I thought it was safe. If that happens, LifeLock gives you a U.S.-based restoration agent who will stick by your side from start to finish. Phone calls, filing documentation, preparing insurance claims, your agent handles it all.

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