William sent in a couple of links to the re-assessment of the 1859 Carrington Event. See for example https://www.earth.com/news/carrington-event-biggest-solar-storm-history-radiocarbon-earth-tree-rings …. scientists have found a new way of pinpointing big solar storms – by analysing the radiocarbon concentration in tree rings. The universities of Helsink and Oulu in Finland were able to detect a spike in radiocarbon from the Carrington Event. More problems for the reliability of C14 dting – as spikes infer injections of radiocarbon into the atmosphere. It must be happening every time there is a big earth facing CME.
We now have a ‘dynamic atmospheric carbon transport’ model, specifically developed for describing geographical differences in the distribution of radiocarbon in the atmosphere. It has opened up new avenues to investigate large solar storms. Significant geomagnetic storms also occurred in 1730 and 1770 – and beyond the 18th century there must be more awaiting diescovery.