You've got to remember this guy is speaking from the perspective of a biologist. To him an economic events like the like the Global Financial Crisis are pretty much irrelevant. Even if global warming had a an effect like 50 years of GFC it wouldn't harm the world biologically but it would totally suck to live through.

Even if the necessary relocation of many people happened in an orderly fashion the cost would be huge. Imagine cost of abandoning most of a significant city because the climate could no longer support the population.