15 Our study coded the positions of documents on climate change as “serious” by assigning ‘Impact Points’ throughout each document based on its positions on climate change as having known or predicted negative impacts (for example, geophysical, economic, or sociopolitical). The reader is directed to table 4 and the supplementary information of Supran and Oreskes (2017) for all individual references to such impacts, and to section 3.2 of the study for a detailed discussion of our results. In short, yes, we observed systematic discrepancies between document categories on climate change as serious. The more publicly accessible documents were, the more they tended to communicate doubt: • ExxonMobil’s peer-reviewed publications focus almost exclusively on methods and mitigation. Only 10 discuss the potential impacts of climate change, of which 60% take a position of ‘Acknowledge’, 30% of ‘Doubt’, and 10% of ‘Acknowledge and Doubt’. Hoffert et al. (2002), for example, warned that unchecked greenhouse gas emissions “could eventually produce global warming comparable in magnitude but opposite in sign to the global cooling of the last Ice Age…Atmospheric CO2 stabilization targets as low as 450 ppm could be needed to forestall coral reef bleaching, thermohaline circulation shutdown, and sea level rise from disintegration of the West Antarctic Ice Sheet” [56]. • Internal documents typically acknowledge the potential for serious impacts but also highlight uncertainties. Of the documents with a position, 35% ‘Acknowledge��� and 47% ‘Acknowledge and Doubt’. An example of doubt is a 1981 report stating “that it has not yet been proven that the increases in atmospheric CO2 constitute a serious problem that requires immediate action” [57]. A characteristic acknowledgement is found in a 1980 Exxon memo, which says, “There are some particularly dramatic questions that might cause serious global problems. For example, if the Antarctic ice sheet[,] which is anchored on land, should melt, then this could cause a rise in the sea level on the order of 5 meters. Such a rise would cause flooding in much of the US East Coast including the state of Florida and Washington D.C.” [58] (see also [29]). A 1979 Exxon memo summarizes several points about potential impacts, for example [27]: - “The most widely held theory is that…the present trend of fossil fuel consumption will cause dramatic environmental effects before the year 2050.” - “Recognizing the uncertainty, there is a possibility that an atmospheric CO2 buildup will cause adverse environmental effects in enough areas of the world to consider limiting the future use of fossil fuels as major energy sources.” - “This study reviews various world energy consumption scenarios to limit CO2 atmospheric buildup”, referring to its appendix summary of “Ecological consequences of increased CO2 levels” reproduced from a 1969 peerreviewed article. The study’s “No Limit on CO2 Emissions” scenario anticipates that “a doubling of the pre-industrial concentration occurs around