IntCal

IntCal is a set of internationally agreed radiocarbon calibration curves used to convert radiocarbon ages into calendar ages. The curves are maintained by the IntCal Working Group, an international collaboration within the radiocarbon community.

The curves synthesize dendrochronologically dated atmospheric 14C records from tree rings, corals, and other archives spanning tens of thousands of years. They reflect fluctuations in atmospheric 14C caused by changes in solar activity, Earth's magnetic field, and other factors, and allow calendar-age interpretation with stated uncertainties.

Historically, calibration curves have been released as successive versions: IntCal04, IntCal09, IntCal13, and IntCal20 (the latter published in 2020). IntCal20 extends calibration back to about 55,000 calendar years before present. For hemispheric differences, SHCal series (e.g., SHCal20) cover the Southern Hemisphere, and for marine samples Marine20 provides corrections for marine reservoir effects.

Uses include archaeological dating, paleoclimatology, and earth science; they underpin radiocarbon dating results produced by software such as OxCal and Calib. By combining radiocarbon measurements with the curves, researchers obtain calendar ages with confidence intervals.

The IntCal curves are publicly available and widely used; new versions are released as new data and methods become available.