Radiocarbon production and cosmic radiation events: current state of the evidence

Past spikes in atmospheric radiocarbon production, initiated by intense bursts of cosmic radiation, have drawn interest from a wide range of research fields. In fact, an entirely new and interdisciplinary subfield of isotope science has developed around them. In May 2025, the outstanding questions and future directions of this subfield were the focus of a Royal Society meeting in Edinburgh. Here, we review the current state of the evidence pertaining to the discovery, verification, origin and implications of these anomalous cosmogenic radionuclide (CRN) production events. We go on to discuss the key issues that need to be resolved for a comprehensive understanding of these phenomena to be achieved. This article is part of the Theo Murphy meeting issue 'Radiocarbon and cosmic radiation events'.