In spite of economist's claims, climate policy instruments such as carbon taxes are rarely implemented. This paper analyzes the drivers of carbon taxes acceptability in the semi-direct democratic context of Geneva, Switzerland. Based on a sample of more than 300 individuals, we assess the effect on acceptability of socioeconomic characteristics, environmental attitudes, social norms as well as individual's perceptions of carbon taxes advantages and disadvantages. We also show that policy design matters for acceptability, in particular earmarking for environmental purposes, and find evidence of an effect of labeling, "climate contribution" leading under some circumstances to larger acceptability than "carbon tax". We infer that proper policy design coupled with effective communication on the effects of carbon taxes may lead to a substantial improvement in acceptability.