Next-generation radiocarbon calibration: Incorporating information on calibration curve covariance

A 6-month project to investigate the effect on radiocarbon calibration of covariance information within the IntCal20 radiocarbon calibration curve. Radiocarbon (14C) provides the most common method for dating the last 55,000-years and underpins the breadth of the environmental and archaeological sciences. Due to fluctuations in past levels of 14C, radiocarbon dating requires calibration against the internationally-agreed IntCal calibration curves.

Traditionally, these IntCal calibration curves provide pointwise estimates of past 14C levels that are treated as independent from one year to the next. This independence suggests the true 14C level could change from the bottom of the uncertainty envelope in one year, to the top of the interval in the next, and then back to the bottom again. This extreme variability is unrealistic.

In reality, the curve estimate has covariance - we expect it to vary more slowly over time within its uncertainty envelope.

When calibrating multiple 14C determinations, essential for much environmental modelling, this covariance matters. The novel approach to curve construction implemented for the recent IntCal20 curves enabled storage of individual calibration curve realisations (which were summarised for the published pointwise IntCal20 estimates). Each realisation represents an entire plausible 14C history from 55,000 - 0 cal yr BP and encodes the curve covariance.

This project aims to explore the effect of using these realisations (and hence covariance information) rather than pointwise calibration. Our findings have the potential to rewrite the way we calibrate.