Carbon dioxide removal (CDR) technologies may be needed to meet climate change targets. A full understanding of public attitudes towards such approaches is currently lacking. Here we report a mixed-methods study on public perceptions of CDR in the United States and the United Kingdom, focusing on bioenergy with carbon capture and storage, direct air capture and terrestrial enhanced rock weathering. A discourse of climate urgency had a substantial impact on perceptions, with CDR seen as offering too slow a response to the climate crisis. CDR also fails to reflect long-term hopes for a sustainable world, being interpreted as not addressing the root causes of climate change. A social license to operate may therefore depend on resolving these temporal dilemmas regarding both the short- and long-term implications of technology development. While research under well-controlled conditions is likely to be acceptable, at-scale deployment without corresponding efforts to reduce emissions may represent a red line for many people.