an additional 1% migration rate would increase world GDP by about 1% (i.e. about one trillion dollars)
I am having strong doubts about this number. The paper cited is long on handwaving and seems to be entirely too fond of expressions like "should make economists’ jaws hit their desks" and "there appear to be trillion-dollar bills on the sidewalk". In particular, there is the pervasive assumption that people are fungible so transferring a person from a $5,000 GDP/capita economy to a $50,000 GDP/capita economy immediately nets you $45,000 in additional GDP. I don't think this is true.
Sure, a randomly chosen person in a $5,000 GDP/capita economy is unlikely to make $50,000 no matter where you move them, but no-one is proposing to move people at random.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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