Why should I bake baking soda for making ramen noodles? I see this recipe for ramen noodles ("alkaline noodles") that says to use bicarb / baking soda that is baked in a very slow oven for an hour (250F / 120C) before incorporating into the noodle dough. Is it necessary to bake the bicarb? What does baking do?

The New York Times has an article about baked baking soda, which says that baking transforms the sodium bicarbonate into sodium carbonate (NaHCO3 into Na2CO3?) but this seems strange; does this really work or is it safe? Am I creating hydrogen gas or presumably harmless water vapor and carbon dioxide?

If it is worth doing for some reason, then there are the ancillary questions. How do I know when it's "done" baking? Both seem to be nondescript white powders. Will a different compound result, after dissolving both in water? Are there any safety concerns with sodium carbonate?
Baking turns bicarbonate of soda into a weak form of lye - sodium carbonate, as you said. It basically makes it a stronger alkali. The actual baking process is safe, but the resulting lye is an irritant and you should avoid getting in on your skin, and definitely avoid it getting it in your eyes.

The difference in texture and colour is noticeable after baking. The texture will be finer, and it will be whiter.