It said that the Lord Ruler moved the planet too close to the Sun and it became too hot. So he kicked the ashmounts awake and let the ash cover the atmosphere and cool the planet down to a habitable temperature.
But I was under the impression that a lot of ash would lead to a greenhouse effect and cook the people much faster. So how does it work actually?
The sulfur dioxide that spewed from the mouth of the volcano created a haze far up in the stratosphere, the upper limits of our atmosphere. The haze reflected sunlight away from the Earth, cooling the planet by almost 1 degree Farenheit (half a degree Celsius) over the two years that followed.
-Muse magazine, April 2010
So this is based off of real-life science. Volcanoes can cool the world.
A thick layer of ash, like from a volcano, would block the sunlight. The greenhouse effect has to do with letting light, and heat, in but not out, through translucent gasses - but the eruption would cause a cloud of ash and dust, one that is opaque. It would reflect both light and heat, so the area beneath it would be cooler... like it is cooler to sit in the shadow instead of the sun, or cooler in the winter when we're getting less warmth from the sun because of the tilt. So the planet would keep getting cooler until the ash was all settled - which might take a while depending on how much dust was made, and how much keeps getting picked up by the wind.
We're talking about the mechanism that killed the dinosaurs. Or a theoretical "nuclear winter." We're also talking about the mechanism that makes it cooler when you sit in the shade of a tree or an umbrella. The particles that make the ash, when airborne, block the incoming light and energy of the sun. Same as dust from the meteor impact that caused the Earth to cool and eventually killed off the dinosaurs.
