Actually, the Si Wong desert would suddenly be arable as the Sahara was during the big ice ages, and a whole big chunk of the Earth Kingdom would suddenly be able to support a bigger population. An ice age would be a mixed bag.

That's why Ozai has a certain amount of power left in this world. He controls the biggest source of hand-me-down loot. Also, manufactured goods don't last as long as they should. Everything's going to rot.