Americans\' attitudes toward climate change are polarizing, with both skepticism and alarm increasing during the last decade, a Yale University survey found. Researchers say the images and emotions the American public associates with global warming shifted significantly between 2002 and 2010. Associations Americans have with the phrase \"global warming\" have changed over time, they said, most notably on the negative or \"naysayer\" side, with images such as \"hoax\" increasingly cited. Meanwhile, \"alarmist\" images of disaster such as the \"end of everything\" increased. Four nationally representative surveys formed the basis of the study. In the surveys, using a form of free association, respondents were asked to provide the first thought or image that came to mind when they heard the term \"global warming.\" Associations were analyzed to identify the nine most common themes -- ice melt, heat, nature, ozone, alarmist, flood/sea level, climate change, weather and naysayers. Analyzing affective imagery \"provides a powerful tool to measure, track, and explain shifting public perceptions of risk over time,\" the researchers said, noting that many Americans perceive climate change as distant and abstract and \"outside of most people\'s direct experience.\" Results of the survey appeared in the journal Risk Analysis, published by the Society for Risk Analysis. No margin of sampling error was reported.