A Sixth Mass Extinction? How linguistic uncertainty shapes our understanding of the biodiversity crisis

The term “sixth mass extinction” has become synonymous with the current biodiversity crisis. However, despite a general agreement that current biodiversity declines are severe, no consensus has been reached on whether this constitutes a ‘mass extinction event’, and thus whether our current situation is comparable to the catastrophic extinction events of deep time. Here we suggest that our inability to gauge whether the current biodiversity crisis is a mass extinction event may lie less in quantifiable evidence and more in the language used to define such events. We highlight areas of linguistic contention, vagueness, and epistemic dispute, and discuss the role of post-hoc decision-making and language in shaping our understanding and communication of biodiversity loss. Our discussion raises larger questions about how we communicate science to the public, funders, and other scientists, and how we use language to both shape awareness and leverage action.