Terrestrial effects of possible astrophysical sources of an AD 774-775 increase in 14C production

TL;DR

This paper investigates potential astrophysical sources for the AD 774-775 14C increase, suggesting a solar proton event as a plausible cause without catastrophic consequences, and discusses implications for modern technology.

Contribution

It provides a detailed analysis of solar proton event scenarios explaining the 14C increase, challenging the CME hypothesis and assessing biological and technological impacts.

Findings

A solar proton event with fluence slightly above October 1989 levels can explain the 14C increase.

Hard spectrum events cause moderate ozone depletion without mass extinction.

Soft spectrum events are ruled out due to severe ozone depletion and biological impacts.

Abstract

We examine possible sources of a substantial increase in tree ring 14C measurements for the years AD 774-775. Contrary to claims regarding a coronal mass ejection (CME), the required CME energy is not several orders of magnitude greater than known solar events. We consider solar proton events (SPEs) with three different fluences and two different spectra. The data may be explained by an event with fluence about one order of magnitude beyond the October 1989 SPE. Two hard spectrum cases considered here result in moderate ozone depletion, so no mass extinction is implied, though we do predict increases in erythema and damage to plants from enhanced solar UV. We are able to rule out an event with a very soft spectrum that causes severe ozone depletion and subsequent biological impacts. Nitrate enhancements are consistent with their apparent absence in ice core data. The modern technological implications of such an event may be extreme, and considering recent confirmation of superflares on solar-type stars, this issue merits attention.