 Why was there fear for the wind shifting around the Hairy People?
Here at least the air was thick enough to support life, and somewhere nearby the outlaws who smuggled their precious contraband water into the water-starved domes of North Mars lay hidden. Toward this barrier the spinner bore him, and Rolf was content to let it move in that direction—from the heights of the wall he could scout out the country beyond. And the barrier became a jumbled mass of roughly-dressed stone slabs, from whose earth-filled crevices sprouted green life. So slowly was the spinner dropping that the blackened desolation of the other hemisphere came sliding up beneath his boots. Ten steps he took before an excited voice called out shrilly from the rocks ahead. This mysterious world that floated above the cavern floor might be their headquarters.
 The wind would spread the scent of the Earthmen and cause an attack
 They wind would block the mind reading abilties of the Hairy People.  The wind would cause explosions.  The wind would spread the hair from the Hairy People and block vision.  The wind would spread the scent of the Earthmen and cause an attack