Modelling Cosmic Radiation Events in the Tree-ring Radiocarbon Record

Abstract

Annually-resolved measurements of the radiocarbon content in tree-rings have revealed rare sharp rises in carbon-14 production. These 'Miyake events' are likely produced by rare increases in cosmic radiation from the Sun or other energetic astrophysical sources. They have so far been interpreted as extreme solar flares, more than an order of magnitude larger than the destructive Carrington Event, and would pose a serious threat to our technological civilization. To interpret high-resolution tree-ring radiocarbon measurements we have to model the entire global carbon cycle: the radiocarbon produced is not only circulated through the Earth's atmosphere and oceans, but also absorbed by the biosphere and locked in the annual growth rings of trees. Our team have therefore developed 'ticktack', the first open-source Python package that connects models of the carbon cycle and its characteristic response curves with modern Bayesian inference tools. We use this to analyse all public annual 14C tree data, and infer posterior parameters for all six known Miyake events. They do not show a consistent relationship to the solar cycle, and several display extended durations that challenge either astrophysical or geophysical models.