Empirical flare energy limits for the largest historical sunspots

Extreme solar particle events (ESPEs) reveal that the Sun can occasionally produce eruptions significantly more energetic than those observed in the modern era. These events are thought to originate from powerful coronal mass ejections (CMEs), typically associated with large solar flares triggered by magnetic field reconnection in complex active regions (ARs). Stellar observations indicate that Sun-like stars can host 'superflares' exceeding 1034 erg roughly once per century, yet it remains uncertain whether the Sun can reach such flare energies. We empirically estimate the upper limit of solar flare energies using statistical relations between flare-ribbon areas and released energy derived from modern observations. By extrapolating these upper-envelope relations to the largest sunspot group recorded since 1859-the Great Sunspot of 8 April 1947-we find that exceptionally large and complex solar ARs could, in principle, produce flares with bolometric energies of a few ×1034 erg. This article is part of the Theo Murphy meeting issue 'Radiocarbon and cosmic radiation events'.