A central conceit of George R.R. Martin’s A Song of Ice and Fire books (and the popular HBO series Game of Thrones based on them) is that the seasons of the planet where they take place are not as predictable as the Earth’s annual cycle. Somehow the phrase “winter is coming” wouldn’t seem as foreboding if you could reply, “Yes, that usually happens in December through February.”

But how could a planet have unruly seasons? Earth’s seasons are due to the tilt of its axis. During one part of Earth’s orbit, the Northern Hemisphere is tilted away from the Sun, with the resulting indirect sunlight spread thin over the surface of the hemisphere, causing winter. On the opposite side of its orbit, summer comes as this hemisphere is tilted toward direct sunlight. There isn’t much room in such clockwork for randomness.

Well, if you’ve ever wanted to debate fan theories, here’s an excellent new resource for you to draw from: a real climate model simulation of Westeros and Essos.

The study appears to have been published by one Samwell Tarly, who notes an affiliation to The Citadel in Oldtown—and also The University of Bristol in the UK. (The effort bears a frankly suspicious resemblance to a climate model of Middle Earth created by a Radagast the Brown.) The new paper comprises what is apparently the very first issue of The Philosophical Transactions of the Royal Society of King’s Landing, a new journal that should not be confused with the long-lived (and nearly identically named) publication of the UK Royal Society. And yes, it is available in the languages of Dothraki and High Valyrian.

The goal of this bit of fun was to see if there was a way to simulate Martin’s world by tweaking a climate model of the Earth. The author took some liberties to fill in the partial map of the “known world” in Martin’s books. And while fan explanations for Martin’s strange and long-lasting seasons have included wild variations of greenhouse gases to volcanic activity to ocean circulation patterns, the author finds these lacking, as there is at least one mention of shortened days during the long winter.

That points to an orbital mechanism. The author’s idea is this: if the planet’s axis wobbled in a circle once per orbit, the summer hemisphere could stay pointed at its equivalent of the Sun the entire time. The first attempt to simulate this configuration crashed the model as intense winds developed between the hemispheres, which reached radically different temperatures. But reducing the planet’s tilt from 23.5 degrees to 10 degrees smoothed out the extremes.

In a winter configuration, most of The North freezes, while much of the rest of Westeros actually stays pretty warm. And that’s especially true on the western side of the continent, which is warmed by ocean currents. During summer, on the other hand, only a small refuge north of The Wall stays frozen (a likely hibernation spot for White Walkers, the author notes. Warm, southern Westeros is bathed in tropical rain.

Referencing some weather data for the “real” Earth—apparently discovered on some dusty shelf of The Citadel Library—the author also finds some close comparisons. The winter climate at The Wall, for example, is similar to northern Sweden and Norway. At Casterly Rock—home to the Lannister family—summer conditions are equivalent to parts of eastern China or Houston, Texas.

There is, however, a major problem with this proposed explanation for long, unpredictable seasons. It seems to work pretty well for describing any single season, but needs a little deus ex machina to actually change from one season to another. There’s no good way to flip the odd orbital behavior that keeps one season locked in, leaving the young Tarly to posit “a passing comet or just the magic of the Seven.” How a suggestion like that slipped through peer review is unclear.

What’s more, the paper notes instances of characters in Martin’s books of navigating by the stars—which would be difficult if the constellations in the sky were rotating in an annual circuit.

At any rate, the paper also includes a measure of the GoT world’s sensitivity to changes in greenhouse gas concentrations. This is in response to reports of measured increases “likely due to the recent increase in dragon population in Essos, the deforestation of many regions associated with the increase in shipbuilding throughout Westeros and Essos, and the excessive use of wildfire.”

The simulations show about 2.1 degrees Celsius of warming for a doubling of the greenhouse gas concentration. That’s slightly less than the roughly 3-degrees best estimate for Earth, but this simulation could only run for 100 years, whereas simulations of Earth typically require several centuries to reach equilibrium.

Noting the potential impact of sea-level rise on King’s Landing, the author writes, “[A]s a climate scientist, I strongly encourage all the Kingdoms of our planet to reduce their emissions of carbon dioxide and seek alternative ‘renewable’ energy (such as windmills).”

On a slightly more serious note, Tarly’s light-hearted experiment is meant to help illustrate the value of climate models. They allow us to investigate our current world, or Earth’s past or future, or even another planet entirely—fictional or not. And as for the physically unavoidable consequences of an increased concentration of greenhouse gases on this planet or any other, a Dothraki saying comes to mind: “It is known.”

https://arstechnica.com/?p=1236459