Is winter really coming? The science behind the weather in Game of Thrones

Warning: spoilers. 

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"Winter is Coming": the prophetic motto of House Stark. The meaning behind the motto is the warning of the darker days to come. The motto was first uttered by the late Ned Stark in the first episode of the first season of Game of Thrones. It is the pillar that holds the complex amalgamation of Game of Thrones' corrupt politics, brutal truths, allegiances, love, and sex. Lots of it. (Well, in the TV series that is.)

At face value, the meaning is starkly obvious: things are going to get cold as fuck for an extended period of time (many years – a year in Game of Thrones is measured the same way as it currently is for us – 3651/4).

In George RR Martin's continent Westeros, the seasons are long, extreme and unpredictable. On Earth, seasons are mostly quite the opposite. So can science explain Game of Thrones' seasons? Sure.

A wobbly axial tilt

The Earth's fixed axis is tilted at an angle of 23.5 degrees from the plane of its orbit around the Sun. This fixed axis is further stabilised by our imposing moon's gravitational tug. The intensity of light energy received in the northern and southern hemispheres is dictated by Earth's location on its orbital plane.

In this example, summer solstice occurs in the northern hemisphere on the left side of the Sun and winter solstice on the right. Both the spring and autumnal equinox receive equal (hence equinox) amount of light energy on the northern and southern hemisphere (seasonal growth changes in plants, ie phenology, mostly give each season its mien):

Image: Nasa

If the Earth's axial tilt wasn't stable, its tilt would be extremely wobbly, resulting in arbitrary seasonal lengths much like in Game of Thrones.

Tilt all over the place. Image: Reddit

In A Game of Thrones (A Song of Ice and Fire, Book 1)/"The Kingsroad" (the second episode of the first season of Game of Thrones), when Daenerys Targaryen's dragons were nothing but embryos gastrulating in eggs, she heard the legend about a world where Westeros and Essos had two moons, "but one wandered too close to the sun and cracked from the heat. A thousand thousand [one million] dragons poured forth, and drank the fire of the sun." If the legend is true, some sort of cataclysmic celestial event could have caused the loss of the second moon, shifting the planet's axis in an irregular fashion.

It is believed that about 5bn years ago when the Earth was young, an asteroid crashed into Earth, giving it the tilt it has today. The accident was nothing short of a miracle. However, if that same accident (or equivalent, say a nuclear explosion powerful enough to tilt the Earth) were to happen today we wouldn't be so lucky...

An elongated orbit

It would be reasonable to assume that the further away the Earth is from the Sun, the cooler the Earth is. But as science is the opposite of common sense, this isn't the case. The Earth's orbit isn't a perfect circle – it's a little lopsided. Our distance from the Sun at the aphelion point, ie Earth's farthest point from the Sun, bears little to no impact on the Earth's climate (though climate scientists believe it could account for the southern hemisphere's moderate winters). In fact, the Earth is farthest from the Sun in the summer and closet to the Sun in the winter.

The world of Game of Thrones may have an elongated orbit:

Diagram by Tosin Thompson; planet image from Reddit

This elongation would mean the world of Game of Thrones is extremely far from its sun at the aphelion point, which would explain Westeros' long and severe winters. Conversely, during perihelion, ie Earth's closest point to the Sun, the world would have a prolonged summer. This weather pattern is evidenced on Mars.

The problem with this theory is that, unlike what we witness in the Seven Kingdoms of Westeros, it is patterned and predicable. The people of Westeros would experience typical seasonal cycles of a fixed length. So although feasible, the theory on its own isn't very plausible.

Complex Milankovitch cycles

Milankovitch cycles were developed in the Thirties by Serbian mathematician Milutin Milankovitch and describe the changes in the way the Earth orbits the Sun. The concept suggests that (1) every 100,000 years, Earth's orbit changes from nearly circular to slightly elliptical (eccentricity), affecting other planets in the Solar System, (2) every 41,000 years, the angle of tilt of the Earth's axis changes from 22.1 degrees to 24.5 degrees and (3), every 26,000 years, the direction of the tilt of the axis changes.

Milankovitch cycles slowly change the climate on Earth, normally resulting in colder winters in the northern hemisphere. The cycles are indicative of the fact that ice ages occur every 100,000 years (we're apparently slap bang in the middle of the cycle – the current warm climate we're experiencing may last another 50,000 years).

Game of Thrones seemingly has much shorter Milankovitch cycles in a decade or less, therefore the cycles are likely to be more irregular and complex. 

Oceans, currents and winds

Oceans, currents and winds are factors that can profoundly influence a region's climate, and are themselves, subject to cyclical variations. Currents such as El Niño and La Niña impact on regional climates across timescales as long as five or more years. Westeros may be subject to such long-term weather trends. 

Westeros' geography may be quite different from Earth's; it could have larger oceans, taller mountains, more violent currents and more blustering winds – all of which is a potential recipe (with a sprinkle of magic) for unpredictable and long-term weather trends.

A combination of some or possibly all these factors could be explanations for Game of Thrones' seasonal variability. So winter might be coming.

Tosin Thompson writes about science and was the New Statesman's 2015 Wellcome Trust Scholar.