Worldbuilding for a fantasy novel

[ChrisShield]

Hi all,

I'm building a world for a fantasy novel. The world is very Earth-like in terms of size, gravity etc, and has a moon similar to ours also.

One of the main aspects of my story is that every four years, the winter in the northern hemisphere is particularly long and brutal. But it only occured to me recently that, although it won't be explained in the novel (it is set in a medieval time period) I would like to know myself why and how, without using the easy route of saying 'because magic'.

I'm no scientist but I understand how our Earth spins on it's axis causing our seasons as we know them, and this was caused by Theia (most likely) smashing into our young planet eons ago.

But in terms of physics, how could this harsher winter be explained? Could it be something to do with the axis not being particularly stable (as in the north pole's precise location shifting)? The issue I had with this theory is the regularity of the winter being harsh every fourth year.

If there isn't a possible scientific theory as to how this could happen, then I'm considering removing the regularity of the harsh winters altogether.

[iNow]

5 minutes ago, ChrisShield said:

But in terms of physics, how could this harsher winter be explained? Could it be something to do with the axis not being particularly stable (as in the north pole's precise location shifting)? The issue I had with this theory is the regularity of the winter being harsh every fourth year.

Ocean currents. Think of phenomena like La Nina and El Nino, just more intense and instead of happening every 9-12 months they happen every 30-36 months. 

https://www.weather.gov/media/owlie/2018_ENSO.pdf

[Ghideon]

32 minutes ago, ChrisShield said:

But in terms of physics, how could this harsher winter be explained? Could it be something to do with the axis not being particularly stable (as in the north pole's precise location shifting)? The issue I had with this theory is the regularity of the winter being harsh every fourth year.

Solar activity.

According to wikipedia attempts to correlate weather and solar activity have had limited success but it may still be useful as a starting point in a work of fiction. 

 

Quote

The solar cycle or solar magnetic activity cycle is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the solar surface. 

https://en.wikipedia.org/wiki/Solar_cycle

You could change the 11 years to four years and make it have more impact on the planet.

 

There are papers discussing connection between the 11-year cycle and for instance tree-rings. So in my opinion it would not be too unscientific have a fiction solar system where harsh winters occur due to solar cycle. 

Quote

Large woody tree trunks from the early Permian Fossil Forest of Chemnitz, southeast Germany, show a regular cyclicity in tree-ring formation. The mean ring curve reveals a 10.62 yr cyclicity, the duration of which is almost identical to the modern 11 yr solar cycle.

https://en.wikipedia.org/wiki/Solar_cycle#cite_note-Luthardt2017-10

 

 

[studiot]

53 minutes ago, ChrisShield said:

One of the main aspects of my story is that every four years, the winter in the northern hemisphere is particularly long and brutal. But it only occured to me recently that, although it won't be explained in the novel (it is set in a medieval time period) I would like to know myself why and how, without using the easy route of saying 'because magic'.

It is not necessary to expect your planet / moon system to create this weather on its own.

There could be a conjunction with other bodies in its solar system that shaded it or passed it through a dust cloud every 4 years, or near an eccentrically orbiting body or somesuch.

Many succesful SF stories have been built on variations of this from The Dragons of Pern to the short stories of The Unorthodox Engineers.

[iNow]

49 minutes ago, studiot said:

It is not necessary to expect your planet / moon system to create this weather on its own.

There could be a conjunction with other bodies in its solar system that shaded it or passed it through a dust cloud every 4 years, or near an eccentrically orbiting body or somesuch.

Many succesful SF stories have been built on variations of this from The Dragons of Pern to the short stories of The Unorthodox Engineers.

I like this idea... like another moon or planet crosses between the planet and the star every 4 years causing long lasting shadows and extreme cold. Nice +1

[DeepSeaBase]

Algae blooms that sequester co2 then after dying they rot and give back co2.

 

Mantle plumes that warm the ocean some.