Aristotle's Climate Model

Greek philosopher Aristotle may have written the first treatise on Meteorology, around 350BC. He postulated the existence of five geographical zones: Frigid (one North, one South) by the poles, Torrid (North and South of the Equator) and Temperate (one North, one South) in-between the relative Frigid and Torrid zones.

Remarkably, that subdivision still holds. One of Aristotle’s ideas has not survived the test of time though: contrary to his thoughts, the Torrid Zone is not devoid of life and especially of human life due to excessive warmth.

And so we can say that Aristotle was totally wrong. Or was he?

Let’s perform some quick computations using modern readings and the world as known by ancient Greeks.

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Consider Alexandria and Aswan, in Egypt, the cities used by Eratosthenes of Cyrene to measure the accurately measure the size of the Earth (around a century after Aristotle’s time).

From the BBC Weather website, temperature statistics for both cities can be computed

Alexandria (31 degrees North):
Average monthly Min: 17.3C
Average monthly Max: 24.9C
Average yearly: 21.1C

Aswan (24 deg N):
Average monthly Min: 19.1C
Average monthly Max: 34.25C
Average yearly: 26.7C

Now, since we know there are 7 degrees of latitude between the two cities, we can compute at what rates temperatures increase going south from Alexandria to Aswan:

Temperature increase by degree of Latitude:
Average monthly Min: 0.26C/deg
Average monthly Max: 1.33C/deg
Average yearly: 0.798C/deg

What is the expected temperature at the Equator (Latitude: zero, thus 24 degrees south of Aswan), assuming those rates don’t vary (i.e. temperature trends can be modelled in linearly)?

Equator (zero deg):
Expected Average monthly Min: 25.5C
Expected Average monthly Max: 66.3C
Expected Average yearly: 45.85C

Look at those temperatures…if those were true, truly the Equator would be more or less uninhabitable.

Therefore: Aristotle’s idea of a “Torrid Zone” was not a philosophical fantasy, but a reasonably estimation compatible with what was known during ancient times.

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Of course we know the actual values are different. For example:

Kinshasa (4 deg N):
Average monthly Min: 20.7C
Average monthly Max: 30.4C
Average yearly: 25.5C

That makes Aristotle’s Climate Model wrong of an amount between 5C and 36C.

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So what are the lessons to take home?

(1) Climate models that appear perfectly reasonable today can be shown to be very, very wrong tomorrow

(2) Extending a trend means just making an estimation that can be way off reality, especially if the trend is presumed linear

(3) Temperature is NOT everything. Actual climate depends on a lot of other things.

At the Equator, like everywhere else on the planet.