Americans increasingly accept that global warming is happening and a serious threat. Using secondary data from national probability surveys of the US adult population and preregistered hypotheses, we explore how and why Americans self-report changing their minds about global warming. Common reasons included learning more about the issue, hearing or seeing the effects of global warming, and personally experiencing its effects. We tested these reasons, as well as additional factors known to influence global warming opinion, including perceptions of social norms, media attention, and exposure to extreme weather, to assess their relative strength in predicting self-reported opinion change. As expected, perceived experience with global warming—particularly vicarious experience or seeing/hearing others experience its effects—emerged as a top correlate, even while statistically controlling for perceptions of social norms and attention to partisan-leaning media like Fox News. Perceived personal experience was a stronger correlate of self-reported opinion change among Republicans, whereas learning more about global warming was a stronger correlate among Democrats. Also as expected, perceiving social norms supportive of climate action was associated with positive self-reported opinion change, particularly among Republicans. Further, attention to the Fox News Channel was associated with negative self-reported opinion change but only among Republicans. Although this research is exploratory and uses self-reported data, it suggests that personalizing and localizing the threat of climate change, and enhancing the norm that most people support action, may be important factors to investigate in future longitudinal research on public opinion change and communication strategies.