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I am writing a work of fiction in which, circa 2030, the global average temperature of the Earth falls by 150C (~270F) over the course of five months. This upends the way societies work as people desperately try to survive.

Due to the speed of the cooling, people will forego rationality and science even more than in the current real world. They will try all sorts of things for heat even though they know they are living on borrowed time.

One of the things that came to my mind is settings forests on fire to heat a small town. Chopping down the trees for fuel would have been smarter, but the clock is ticking and axes are not always available. So somewhere in the world, some group of people is bound to do it.

My question is, how effective would a forest fire be in heating up a catastrofically cooling small town, and if it turns out this is effective, how long could it last?

This question is not about the side effects of the fire, such as ash and soot making it hard to breath. I am already expecting things like these to happen already.

Edit for clarification: people would not wait until the Earth is a solid ice ball to try that stunt. I am imagining people doing that by the time it starts snowing around the equator, which should be much before even a month and a half into the cooling.

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  • $\begingroup$ There wouldn't be any forests to begin with. Unless you are saying this is the first time it's happened. $\endgroup$
    – Firestryke
    Aug 14, 2021 at 20:53
  • $\begingroup$ @firestryke it is. I have edited the beginning of the question to clarify. $\endgroup$
    – The Square-Cube Law
    Aug 14, 2021 at 20:55
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    $\begingroup$ I am not at all certain that one can even start a forest fire at such a low temperature... And anyway everybody would be dead anyway long before the temperature dropped to minus 130 centigrade. $\endgroup$
    – AlexP
    Aug 14, 2021 at 20:55
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    $\begingroup$ I suspect that town will barely feel it; hot gases from combustion rise away and dissipate quickly so most of the energy the town gets is from radiation, which drops off as the square of distance. So there's a bit of warmth from the burning trees nearest the town, dropping off rapidly. Beyond that, AlexP raises a good point; at -130 C, a lot more energy is required to heat up wood to ignition temperature, making it somewhat more difficult for the forest fire to spread. $\endgroup$
    – GrumpyYoungMan
    Aug 14, 2021 at 21:32
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    $\begingroup$ Setting the forests on fire has other effects. It releases a lot of carbon dioxide which helps warm up the world again. It reduces the cooling effect of tall vegetation. There is a suggestion that the Little Ice Age in Europe was caused by the reforestation of North America after the introduction of European diseases wiped out the people who had been regularly burning the forests. $\endgroup$
    – David R
    Aug 15, 2021 at 14:17

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Although fire burns at very high temperatures, the temperature drops exponentially the further you move away from it. Just like when you stand close to a house fire, you can feel the heat, but when you move slightly back, you don't feel it at all anymore.
It's the same with forest fires - they will drastically heat up the area they are in (to the point of destroying it), but anything that's farther away from the fire will barely get heat up.
So the only houses that would receive the heat are the ones that are very close to the forest, but they would have to be in a perfect spot where they are close enough to receive the heat while being far enough that the fire doesn't spread and burns them down. Any other house won't even notice the heat. And even then, the heat would last for at most a few hours and you just wasted the whole forest, so it would not be worth it.

So essentially, even if we ignore the extremely low temperatures and the fact that a fire in that environment would probably be impossible to start, let alone spread, forest fires would be really inefficient at heating up the town.

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