 Others, including Hubert Lamb, who created a Dust Veil Index, thought volcanoes were more responsible for global-scale aerosol.In 1973, Bryson testified to Congress that global warming from fossil-fuel combustion was politically unstoppable.In later years, when it was clear that the climate was indeed warming, Bryson argued that while climate change and a global increase in temperature are real, he did not believe that they are caused by human activity.