IntCal > History


Although it was recognised in the 1950's that 14C levels in the atmosphere had varied in the past, it was only through developments in dendrochronology and radiocarbon dating that the construction of curves or tables for correction (or calibration) of radiocarbon ages to calendar age estimates was possible. The first curves were published in the 1960's and revised through the early 1980's. In 1986 the first high-precision calibration curve for terrestrial samples was constructed based on measurement of primarily Irish oak and trees from the Pacific coast of North America, but using as well, data from bristlecone pines and German oak. A marine curve based on an ocean-atmosphere box model was also produced. In 1993 uranium-thorium dated corals (reservoir age corrected for use in the terrestrial curve) extended the calibration curves to 21,950 cal BP. In 1998 the curves were updated with more tree-ring measurements and extended to 24,000 years before present (cal BP) by including forams from Cariaco basin varved sediments and additional U-Th dated corals.

Belfast 2002

Belfast 2002: Left to right: Minze Stuiver, Paula Reimer, Tom Guilderson, Gerry McCormac, Warren Beck, Hans van der Plicht, Bernd Kromer, Christopher Bronk Ramsey, Sabine Remele, Caitlin Buck, John Southon, Konrad Hughen, Michael Friedrichs, Edouard Bard, Paul Damon, (not shown) Ron Reimer

In 2001 funding from the Leverhulme Trust, UK, enabled the formation of the IntCal Working Group (IWG) which met at Queen's University Belfast (QUB) and Woods Hole Oceanographic Institute to establish criteria for calibration data and methods for curve construction. In 2004 the IWG released new IntCal and Marine curves which had been further refined and extended to 26,000 cal BP. A calibration curve for the Southern Hemisphere was also developed from tree-ring measurements (SHCal04). In 2006, a NERC grant to QUB and University of Sheffield funded refinements to the statistical methods for curve construction and an IWG meeting. The IWG extended the curves to 50,000 cal BP in 2009 and updated the curves again in 2013. In 2020 the availability of the high definition Hulu Cave speleothem record allowed for the extension of IntCal20 back to 55,000 cal BP. The Hulu cave data served as a backbone for wiggle matching millennial length floating Kauri tree ring records, providing detail to the older portion of the IntCal curve. In addition, a large increase in single year tree-ring records provided higher resolution for the Younger Dryas as well as for the past 5000 years.