In this world, a massive volcanic eruption results in ash being spewed into the stratosphere of an earthlike planet, blocking out sunlight. The explosion is on a similar scale as the Toba Eruption Already, the ash has blocked the sky for five years, and will remain for several more. Humanity must now cluster in dense supercities spattered across the world (with a little arcane help, otherwise I would speculate that they're toast).

This background, if unrealistic can definitely be altered, especially in terms of the harshness of the volcanic explosion and duration of the ash cloud. I am currently undecided on the latitude of the city, which will definitely impact the questions.


What are the environmental conditions as a result of this volcano?

  • Temperature: Obviously, this will decrease. But how much? Will it reach below zero, freezing lakes in rivers? Is this enough to freeze over the ocean?
  • Precipitation: Will this ash cloud in any way reduce or evaporation, or only fall in snow? How does this affect geological features, such as lakes and rivers?
  • Biodiversity: Presumably, many species of plants and animals could no longer live in such a harsh climate. What plants and animals are able to survive?

If you have any other categories that you feel need addressing, go right ahead. These are just some specific elements to narrow down the scope of a broad question.

  • $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$
    – Community Bot
    Commented Jul 15, 2022 at 21:32
  • $\begingroup$ in times of food scarcity the last place you want to live are cities. Also a lot of this is going to depend on geography, If Yellowstone erupted tomorrow south America would barely notice outside trade effects. $\endgroup$
    – John
    Commented Jul 16, 2022 at 3:57

1 Answer 1


The temperature on the surface of the planet will decrease for a few reasons. First, the ash will block out some of the sunlight, leading to less energy being absorbed by the planet. Second, the ash will also reflect some of the sunlight back into space, further cooling the planet. Finally, the ash will absorb infrared radiation from the planet, which will also lead to cooling. However, the infrared absorption will not be enough to offset the other effects, and so the planet will become cooler overall.

Precipitation will definitely decrease, as the ash will block out some of the sunlight that would be used to evaporate water. This could lead to large amounts of standing water, as well as floods when the snow melts.

Biodiversity will be greatly affected by the cooler temperatures and reduced precipitation. Many plants and animals will not be able to survive in such a harsh climate. Only the hardiest plants and animals will be able to survive.


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