October Monthly Meeting – Modelling Cosmic Radiation Events in the Tree-ring Radiocarbon Record

Our meetings include brief business, a main presentation and items of astronomical news or learning from members.

The October Main Item will be: Modelling Cosmic Radiation Events in the Tree-ring Radiocarbon Record  by Dr Ben Pope.
A synopsis of Ben’s talk and a bit about him appears below.

The October 2024 meeting is planned to be a face-to-face meeting; attendees can also join in online via Zoom. Details emailed to members. Guests/visitors can contact us for Zoom details at .
Visitors are welcome to join our face-to-face or online meetings.

Synopsis of the main presentation.
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 civilisation. 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.

Benjamin Pope grew up in Sydney. After graduating with a Masters degree in science from the University of Sydney, he travelled to the University of California, Berkeley and then to Oxford University where he graduated with a DPhil in Astrophysics in 2017. From 2017 to 2020 he was a NASA Sagan Fellow at the NYU Centre for Cosmology and Particle Physics and Centre for Data Science. He returned to Australia in 2020 and is currently Lecturer in Astrophysics at UQ. He has an ARC DECRA Fellowship to support his research on exoplanets.