 By the 1960s, MacDonald was publicly concerned about the potential risks of industrial climate change, both aerosol-induced global cooling and carbon-dioxide driven global warming.MacDonald contributed to the President's Science Advisory Committee environmental report in 1965 and the National Academy of Sciences report in 1966 that warned of such risks.In 1969 he began a JASON project to model climate change that soon convinced him that fossil-fuel burning would lead to dangerous global warming that would outstrip any industrial cooling effects.