i think what happened was the fire and all that that rained from the heavens, not only destroying the life below, blocked out the sun. fire has been shown to actually promote plant growth in some instances, so for all we know after destruction rained from the heavens plants could have overtaken the world.
thats obviously not the case.
instead, the sun is blocked out. plants cant grow, food cant grow, and the people are barely getting by.
back to the topic.
if the crew didnt show up to sign my poster, id go out into the empty green field away from the wrath of lavos. he cant get me where the map doesnt show!