I never quite got the climate change angle, because as a race they're so obviously shown to be a species adapted to desert conditions - it's emphasized several times in the series as well as in some books that they like it dry and hot
. This suggests they have evolved in just such conditions. Of course species can change and adapt, but this takes a lot
of time, and if they're meant to have been living in some sort of lush green environment a mere couple of thousand years or even less ago, then their physiology doesn't make sense.