An Up-HILL Battle: Towards clearer terminology for High-Impact Climate Possibilities, including tipping points

Abstract. Climate science terminology increasingly shapes public and policy discussion, yet shared understanding of commonly used terms is often assumed. This study examines how people make sense of language associated with High-Impact Climate Possibilities (HICPs), sometimes referred to as high‑impact low‑likelihood climate events. Its aim is to inform the development of a glossary to support clearer and more consistent communication across and between specialist, policy and public contexts.

Using qualitative evidence from focus groups, we explored how participants interpreted key terms, how meanings were negotiated through interaction, and how emotional responses emerged. We found that meaning is frequently left implicit, with participants relying heavily on everyday language, personal experience and familiar metaphors when interpreting scientific terminology. As a result, everyday meanings often dominate sensemaking, diverging from scientific intent. Emotional responses were shaped less by the terms themselves than by the context in which they were encountered, including assumptions about timescale, likelihood and certainty that were not explicitly stated.

These findings highlight the risks of relying on assumed shared understanding when communicating HICPs. In response, we propose an evidence‑informed glossary and communication guidance developed through iterative engagement with scientists, policy‑facing colleagues and communicators. The glossary is intended as a practical framework to support clearer, more transparent and more consistent use of language, and as a foundation for further empirical work.