Winter Is Here, but Why?

Winter is coming!

For last six years, we celebrated summer (in the northern hemisphere at least) with the promise of inevitable winter and this year finally winter is here. The Game of Thrones TV show is going to come back in just a few days for its 7th season and this time the Great War in the middle of winter is ahead of us.

Game of Thrones which is inspired by amazing, rich and yet uncompleted stories of G.R.R Martin, is one of the best epic fantasy of our time. The story is happening in another world. Where the magic still exists, dragons are flying and seasons don’t act as they should.

The story so rich, that you can find many social, political and historical interpretations from it. But what we can say — if anything — about the science?

There are many aspects of this story that you can examine by science from the destructive power of wildfire to the stability of the great wall of the north. But let’s just talk about one major issue in this world: the seasons.

You may tell me that this is a magical world and things don’t follow the natural law and the power behind seasons and great winter is magic. That is reasonable but it doesn’t stop us to wonder is there any possibility to witness such irregular behavior in any other world?

Before going further, let's see what we know based on the books and the show about this world...

We know that the world of the GOT has a moon – similar to the Earth which has the moon. But based on some of the old stories this world once had a second moon too.

The 2nd Moon, based on these folklores, had fallen into the sun and during this fall, it gave birth to the dragons for the first time. But even in the World of the Seven Kingdoms, this story is considered a myth.

We also know that probably there are seven planets in this system and that, generally, this star system should be similar to our own solar system.

We know that comets do exist in this world. Remember that red comet? The duration of the day and night is as same as here and probably the orbit of this planet around the sun, judging by how long is one year.

The atmosphere, geology and the gravity are also same as ours. Almost everything is similar to our world. Yes, we don’t have dragons, and we don’t have red comets, but still, most things are similar except the duration of the seasons.

It seems that the seasons in this world don’t follow a natural law. Probably the magic beyond the wall plays a crucial role. However, there must be some kind of regularity. We know that one of the specialties of masters is observing and try to predicate the time of winter and how long it would be last.

So let see if we don’t consider magic, is there any way to find a world, for example, one of the extrasolar planets, in which, such irregular seasons happen.

To answer this question, let’s check what is responsible for the seasons in our own world.

The main reason that the Earth witnesses the seasonal changes is due to its axial tilt in respect with its orbital plane. If you draw a line between the North and the South poles, this line represents the rotational axis of the Earth. The axial tilt of our planet is about 23.5 degrees. (It actually changes between 22.1 and 24.5 degrees on a 41,000-year cycle.)

During the summer of the northern hemisphere, these axes lay toward the sun. This means long days in the Northern hemisphere and more absorbing radiation from the Sun.

At the same time, the other hemisphere of the Earth is laid to the other side, and so receives less sunshine. There are long nights in winter as a result.

Six months later, when Earth reaches the other side of the sun, the situation revises and while winter is coming to the Northern hemisphere, the South enjoys the summer.

This axial tilt is a crucial element for shaping the seasons. Although, not every planet has the same axial tilt.

For example, Venus has an axial tilt of 177 degrees. This means, unlike all other planets of the solar system, it rotates around itself from East to the West. So, if it wasn’t because of clouds on Venus, you could see the sun rises from the West and sets in the East, from the surface of the planet.

And, who knows? Maybe in that planet Khal Drogo could back to live – fully functional – again.

This axial tilt can be different but still, the seasons, would be regular and predictable.

Another parameter that could play a role is the shape of the orbit of a planet around the star. Planets move around their star in an elliptical orbit, which means at some point of their journey, they will be closer to their star and at some point, they will be further.

In our case, the orbit of the Earth around the sun is very close to a circle. We actually are closer to the sun during Northern hemisphere winter than Northern summer. But because of the circle-like the shape of our orbit, this different does not matter as much as axial tilt.

But, if there is a planet with highly elliptical orbit with a high eccentricity, these different distances from the sun could really affect the climate. Still, it is going to be predictable but in combination with axial tilts, it could result in a different kind of seasonal changes.

We can add something more in this mix.

Earth has an almost fixed and stable axial tilt. The moon plays a role in this stability. Remember that according to the myths of the World of Ice and Fire, there was a second moon around this world.

The legends say that sometime in the past (but probably not very long ago in the astronomical scale) this moon went rogue and had fallen toward the sun. So if this legend has a basis in the reality, it is possible that the orbit and also axial tilt of the planet became unstable for a period of time. It actually could result in irregular seasons, but not such a rapid changes, that you could witness in a lifetime or a generation.

If you want to continue to look at the orbital elements of a planet which can affect the seasons and climate, there are still few other options. You can find all of them under the title of Milankovitch cycles. But, none of them could alone explain such irregularity for seasons.

There is another explanation. We don’t know much about this world geography and geology. There is a possibility that geological activities such as volcanoes, hot springs, the release of a vast amount of under surface or underwater methane or carbon dioxide, and the change of the landscape and water circulation, play a significant role on the climate.

Yes, you still have periodical seasons but you also could witness a semi-periodical and short term ice ages, which you can refer it to long winter.

Or, probably a combination of all of these factors is the engine behind these unusual winters. At the end of the day, it seems more logical that the magic is the main player behind the scene in this story.

But, it is still fun to bring something from a fantasy world and try to find out how it could happen in our world.