In this paper, we address the chicken-or-egg question posed by two alternative explanations for the relationship between perceived personal experience of global warming and belief certainty that global warming is happening: Do observable climate impacts create opportunities for people to become more certain of the reality of global warming, or does prior belief certainty shape people’s perceptions of impacts through a process of motivated reasoning1? We use data from a nationally representative sample of Americans surveyed first in 2008 and again in 2011; these longitudinal data allow us to evaluate the causal relationships between belief certainty and perceived experience, assessing the impact of each on the other over time2. Among the full survey sample, we found that both processes occurred: ‘experiential learning’, where perceived personal experience of global warming led to increased belief certainty, and ‘motivated reasoning’, where high belief certainty influenced perceptions of personal experience. We then tested and confirmed the hypothesis that motivated reasoning occurs primarily among people who are already highly engaged in the issue whereas experiential learning occurs primarily among people who are less engaged in the issue, which is particularly important given that approximately 75% of American adults currently have low levels of engagement3,4.