Projections of future warming suggest an increase in global temperatures of 2 to 9˚F during the 21st century, with the former reflecting a manageable outcome if the sensitivity of the climate to increasing greenhouse gas concentrations is small and we take aggressive actions to reduce emissions. The latter, which would make Park City hotter than present-day Salt Lake City, reflects a high-consequence outcome if the sensitivity of the climate to increasing greenhouse-gas concentrations is large and we follow a high carbon emission pathway into the future.