 Bryson's main contribution to the debate on climate change was the idea of "the human volcano" causing global cooling, via an increase in aerosol loading.This idea was sparked in 1962 by his own observation, while flying across India en route to a conference, that his view of the ground was blocked not by clouds but by dust.At the time, the instrumental temperature record did not show unambiguous warming and the view that the earth might be cooling, and heading for further cooling, was not unreasonable.