The American public is poorly informed about the existence and primary cause of global warming. Just 67 percent of Americans are confident in the knowledge that global warming is happening, and a mere 53 percent understand that it’s mostly caused by human activities, while 33 percent of Americans continue to believe that global warming is mostly natural (Marlon et al. 2019). Of the latter, 13 percent believe that humans are not at all responsible for climate change, and a further 5 percent say the climate is not changing; this level of misconception is worse in the United States than any other developed country (Milman and Harvey 2019).
The situation is dramatically different among those who make a career of studying climate change; numerous studies using a variety of survey methods have found that there is a 90-to-100 percent expert consensus on human-caused global warming (Cook et al. 2016). This raises an oft-heard question, which can be loosely phrased as: How do the experts know that global warming is happening, and that humans are the cause? Herein is a summary of the evidence underlying what has been described as a “knowledge-based consensus” (Jacobs et al. 2018).
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